A new analysis of data from “The Biggest Loser” highlights the complex ways the body compensates when we drop pounds.Many of us remember “The Biggest Loser,” the somewhat notorious reality television show that ran for more than a decade starting in 2004, in which contestants competed feverishly to drop massive amounts of weight over a short period of time. One of the biggest lessons of the show appeared to be that extreme exercise, along with draconian calorie restriction, would lead to enormous weight loss. Media coverage of the contestants years later, though, seemed to tell a different story, of weight regain and slowed metabolisms and the futility of attempting long-term weight loss. Now a new scientific analysis of the show and its aftermath, published last month in the journal Obesity, suggests many beliefs about “The Biggest Loser” may be misconceptions. The analysis tries to untangle what really happened to the contestants’ metabolisms and why some of them kept off weight better than others. It also looks into the complex role of exercise and whether staying physically active helped the contestants keep their weight under control for years, or not.For those who may have forgotten, or tried to, “The Biggest Loser” ran on NBC to generally high ratings for more than a dozen seasons. Contestants competed to drop the most pounds using extreme calorie restriction and hours of daily strenuous exercise. “Winners” typically shed hundreds of pounds in a few months.Such rapid and extreme weight loss caught the attention of Kevin Hall, a senior investigator at the National Institute of Diabetes and Digestive and Kidney Diseases, which is part of the National Institutes of Health. An expert on metabolism, Dr. Hall knew that when people drop lots of weight in a short period of time, they typically send their resting metabolic rates — the baseline calories we burn every day just by being alive — into free-fall. A lower resting metabolic rate can mean we burn fewer calories over all. This effect was believed to be caused, in part, by the loss of muscle during dieting. A relatively active tissue, muscle burns more calories than fat, and more muscle typically means elevated metabolic rates. So, Dr. Hall wondered, would the maniacal levels of exercise during “The Biggest Loser” help dieters hold onto muscle and keep their resting metabolism high, even as they cut calories?Starting more than a decade ago, Dr. Hall and his colleagues began the first of a series of experiments to find out. In a study from 2012, they compared 16 men and women who had lost massive amounts of weight by cutting calories, thanks to gastric bypass surgery, and 16 contestants from “The Biggest Loser,” whose extreme weight loss involved exercise as well as dieting. As expected, the bypass group shed muscle, as well as fat, while “The Biggest Loser” contestants kept most of their muscle and primarily dropped fat. But everyone’s resting metabolic rate dropped, and to about the same extent, whether they remained well-muscled or not.Dr. Hall said he and his colleagues were surprised by the results. And their confusion intensified when, for a 2016 study, they rechecked 14 of same contestants six years after their competition, expecting their metabolisms to have rebounded by then. Most dieters’ resting metabolisms rise somewhat after they stop actively losing weight, and especially if they regain pounds. Larger people burn more baseline calories than people who are slighter. By this time, most of the contestants had regained weight. But their resting metabolisms remained stubbornly slow, burning an average of about 500 fewer daily calories than before they joined the show.The next year, a follow-up study concluded physical activity had helped some contestants stave off weight gain. If they moved around or formally exercised for about 80 minutes most days, they added back fewer pounds than if they rarely worked out. But their exercise did not boost their resting metabolisms. The exercisers, in fact, showed the greatest relative declines in their resting metabolic rates.Perplexed, Dr. Hall recently began to reconsider the “Biggest Loser” studies in light of an emerging concept about how human metabolism fundamentally works. This idea grew out of an influential 2012 study showing that highly active hunter gatherers in Tanzania burn about the same relative number of calories every day as the rest of us, even though they move around far more.The scientists involved in that research postulated the tribespeople’s bodies must automatically be compensating for some of the calories they burned while hunting for food by decreasing other physiological activities, such as growth. (The tribespeople tended to be short.) In that way, the researchers felt, the hunters’ bodies could keep the overall number of calories they burned each day in check, no matter how many miles they jogged in search of tubers and game. The scientists called this idea the constrained total energy expenditure theory.Aware of this research, Dr. Hall began to see potential parallels in “The Biggest Loser” results. So, for the new analysis, he looked back at his group’s data for hints about whether contestants’ metabolisms had behaved, in effect, like the metabolisms of the hunter gatherers. And he found clues in their resting metabolic rates. That number plummeted early in their “Biggest Loser” filming, he noted, when they slashed how much they ate, and their bodies, understandably, reduced the calories they burned to avoid starving.But in later years, when contestants typically returned to eating as they had before, their metabolisms stayed depressed because, he concluded — and this was key — most of them still exercised. Counter-intuitively, he wrote in the new analysis, frequent physical activity seems to have prompted their bodies to hold resting metabolic rates low, so total daily energy expenditure could be constrained.“It’s still just a hypothesis,” Dr. Hall said, “but it seems like what we’re observing” in the “Biggest Loser” data “is an example of the constrained energy model.”So, what could this rethinking of “The Biggest Loser” story mean for the rest of us, if we hope to keep our weight under control? First and most fundamentally, Dr. Hall said, it suggests that abrupt and colossal weight loss generally will backfire, since that strategy seems to send resting metabolic rates plunging more than would be expected, given people’s smaller body sizes. When people drop pounds gradually in weight-loss experiments, he pointed out, their metabolic changes tend to be less drastic.Second and more befuddling, if you have lost substantial weight, “Biggest Loser” style, exercise likely will be both ally and underminer in your efforts to keep those pounds at bay. In Dr. Hall’s new interpretation of contestants’ long-term weight control, frequent exercise kept contestants’ resting metabolic rates low but also helped them stave off fat regain. In essence, the contestants who worked out the most wound up adding back the least weight, even though they also sported the slowest relative resting metabolisms.Exactly how, then, exercise aided with their weight maintenance is not yet clear, Dr. Hall said. He suspects that exercise affected people’s appetites in ways that may have made them less prone to overeating, while also burning some extra calories. He hopes to develop future experiments to elucidate how exercise influences metabolisms, for better and worse, he said.For now, though, the most reverberant lesson of “The Biggest Loser” may be that long-term weight loss, although daunting, is not unfeasible. Yes, most “Biggest Loser” contestants regained weight, Dr. Hall said, but not necessarily every pound they dropped. After six years, most still weighed about 12 percent less than before joining the show, a meaningful difference, and the most successful of the former contestants were those who still worked out.

Among 52 incentives to exercise, giving people a 9-cent award if they returned to the gym after missing a workout helped the most.Receiving a tiny monetary reward at the right moment could play an outsize role in motivating us to exercise, according to a large-scale and innovative new study of how to nudge people to show up at the gym.The study, published today in Nature, involved 61,293 American gym members, 30 prominent scientists working at 15 universities, and more than 50 different motivational programs. In addition to reward points, incentives ranged from a free audiobook for gym use to cheery instructions from researchers to reframe exercise as fun. While some of the programs galvanized additional gym visits, others, including some the scientists had absolutely expected to inspire more exercise, did not.The study’s findings, positive and the reverse, offer timely insights into how the rest of us might better motivate ourselves to keep our upcoming New Year’s exercise resolutions. But just as important, the study, in its ambition, scope and structure, is meant to serve as a road map for future investigations into the mysteries of human behavior and why so many of us act as we do and sometimes, despite our best intentions, keep skipping that next spin class.The science of human behavior, including whether and why we exercise, can be squishy and rife with research hurdles. Many past studies have looked at how to build habits, for instance, or instill confidence or stick to an exercise routine. But the vast majority of those studies have been small-scale or homogeneous, recruiting only affluent, well-educated white people, for example, or healthy, young college students, or only men or only women.Those studies have also used a wide range of methods to track behavior change, making it difficult to compare data from one study to another. In addition, many have relied on subjective measures, such as asking people how they feel during and after a study, a topic on which we can be, intentionally or not, untrustworthy. The result has been a replication crisis in behavior science, with researchers unable to repeat the findings of many past studies, calling the original results into question.These issues naturally concerned Katy Milkman, a professor at the Wharton School of the University of Pennsylvania and author of the 2021 book “How to Change” (one of Well’s favorite health books of the year) and her colleague Angela Duckworth, also a professor at Wharton and author of the 2016 best seller “Grit.” Among the foremost behavioral scientists at work today, they were convinced their field could and should become more scientifically rigorous, which led them to begin noodling with the notion of megastudies.A megastudy, as they defined the concept, would be large in scale, involving thousands of participants, and not the dozens commonly used in behavioral research. It would also randomly expose large groups of volunteers to a range of behavior modifications or other interventions, employing objective measures to assess whether an intervention had actually worked.These ideas brought the research team to the 24 Hour Fitness chain. Already, they had decided that one of their first megastudies would concentrate on exercise behavior, in part because it is easy to measure increases or declines in workouts and visits to the gym, but also because encouraging people to exercise more can alter lives by boosting health.With its nationwide network of hundreds of gyms, 24 Hour Fitness offered the researchers millions of potential participants for their massive study. Then they invited dozens of other scientists to come up with interventions they felt would up people’s willingness to work out. They also created an umbrella program, called “Step Up,” which gym members could choose to join, earning Amazon reward points worth about $1.00 once they did. The “Step Up” program promised to provide them with new ways to motivate themselves to work out.Michelle V. Agins/The New York TimesMore than 61,000 members joined the “Step Up” program, after which the scientists divided them into 53 groups. One group, which served as a control, changed nothing about their lives or gym time. The others were then assigned to receive a basic package of motivational help that included advice to plan the exact day and time of each workout, a texted reminder from the research team about those plans, and a minuscule reward if they did work out, worth about 22 cents in reward points. These kinds of efforts can be key to increasing motivation, the researchers felt, and would serve as a baseline test of whether the study was inspiring people to exercise more.On top of this basic package of reminder texts and small rewards, the researchers then randomly assigned the gym members who were not in the control group to one of 52 different motivational programs developed by the researchers. In one, for example, the members earned reward points worth about $1.75 every time they visited the gym; in others, they shared their workouts with friends on social media, signed a fitness pledge to show up regularly or agreed to reflect after each workout on how it had affected them. Each group included at least 455 participants. Each intervention lasted a month.Before and during that month, the researchers tracked how often people turned up at their gym. They also asked outside exercise and behavior experts which interventions they expected would be most successful.The results surprised almost everyone. Dr. Duckworth, for one, told me she had thought encouraging people to view workouts as fun would get them to the gym more often, but that group showed only a minuscule increase in gym visits. (Almost everyone in the intervention groups worked out a bit more often than the people in the control group.)The most successful intervention, though, turned out to be giving people the equivalent of 9 cents’ worth of reward points if they returned to the gym after missing a planned workout. That program increased gym visits by about 16 percent, compared to the baseline package of planning and text reminders. Almost as effective was simply giving people a bigger reward, worth $1.75, every time they worked out. It increased exercise by about 14 percent, compared to the baseline package.Over all, the findings suggest that if we want to exercise regularly in 2022, we should, in general:Plan a reasonable workout schedule;Program reminders of that schedule into our phone or with an admonitory spouse or training buddy; andFind small ways to reward ourselves when we exercise as planned. Drop a dollar into a bowl for every workout, for instance, and let the proceeds mount.Perhaps most important, though, the study’s results show, we should “try not to miss more than one workout,” Dr. Milkman said. Getting ourselves back to the gym or pool or walking trail or cycling path after skipping one session might have special potency in helping us show up for the next workout, and the next after that.Of course, this study, large and complex as it is, involved only people interested enough in fitness to join a gym, so the results may not apply to everyone else. The interventions also lasted only a month, which could be too short to see behaviors change. Dr. Duckworth and Dr. Milkman, who now co-direct the Behavior Change for Good Initiative at Wharton, are planning other megastudies, related not only to encouraging exercise, but also other major health issues, such as vaccination hesitancy.

Simple activities like walking boost immune cells in the brain that may help to keep memory sharp and even ward off Alzheimer’s disease.Staying physically active as we age substantially drops our risk of developing dementia during our lifetimes, and it doesn’t require prolonged exercise. Walking or moving about, rather than sitting, may be all it takes to help bolster the brain, and a new study of octogenarians from Chicago may help to explain why.The study, which tracked how often older people moved or sat and then looked deep inside their brains after they passed away, found that certain vital immune cells worked differently in the brains of older people who were active compared to their more sedentary peers. Physical activity seemed to influence their brain’s health, their thinking abilities and whether they experienced the memory loss of Alzheimer’s disease. The findings add to growing evidence that when we move our bodies, we change our minds, no matter how advanced our age.Already, plenty of scientific evidence indicates that physical activity bulks up our brains. Older, sedentary people who begin walking for about an hour most days, for instance, typically add volume to their hippocampus, the brain’s memory center, reducing or reversing the shrinkage that otherwise commonly occurs there over the years. Active people who are middle-aged or older also tend to perform better on tests of memory and thinking skills than people of the same age who rarely exercise, and are nearly half as likely eventually to be diagnosed with Alzheimer’s disease. Almost as heartening, active people who do develop dementia usually show their first symptoms years later than inactive people do.But precisely how movement remodels our brains is still mostly mysterious, although scientists have hints from animal experiments. When adult lab mice and rats run on wheels, for example, they goose production of hormones and neurochemicals that prompt the creation of new neurons, as well as synapses, blood vessels and other tissues that connect and nurture those young brain cells.Rodent exercise also slows or halts aging-related declines in the animals’ brains, studies show, in part by strengthening specialized cells called microglia. Little understood until recently, microglial cells are now known to be the brain’s resident immune cells and hall monitors. They watch for signs of waning neuronal health and, when cells in decline are spotted, release neurochemicals that initiate an inflammatory response. Inflammation, in the short-term, helps to clear away the problem cells and any other biological debris. Afterward, the microglia release other chemical messages that calm the inflammation, keeping the brain healthy and tidy and the animal’s thinking intact.But as animals age, recent studies have found, their microglia can start to malfunction, initiating inflammation but not subsequently quieting it, leading to continuous brain inflammation. This chronic inflammation can kill healthy cells and cause problems with memory and learning, sometimes severe enough to induce a rodent version of Alzheimer’s disease.Unless the animals exercise. In that case, post-mortem exams of their tissues show, the animals’ brains typically teem with healthy, helpful microglia deep into old age, displaying few signs of continuous brain inflammation, while the elderly rodents themselves retained a youthful ability to learn and remember.We are not mice, though, and while we have microglia, scientists had not previously found a way to study whether being physically active as we age — or not — would influence the inner workings of microglial cells. So, for the new study, which was published in November in the Journal of Neuroscience, scientists affiliated with Rush University Medical Center in Chicago, the University of California, San Francisco, and other institutions, turned to data from the ambitious Rush Memory and Aging Project. For that study, hundreds of Chicagoans, most in their 80s at the start, completed extensive annual thinking and memory tests and wore activity monitors for at least a week. Few formally exercised, the monitors showed, but some moved around or walked far more often than others.Many of the participants died as the study continued, and the researchers examined stored brain tissues from 167 of them, searching for lingering biochemical markers of microglial activity. They wanted to see, in effect, whether people’s microglia appeared to have been perpetually overexcited during their final years, driving brain inflammation, or been able to dial back their activity when appropriate, blunting inflammation. The researchers also looked for common biological hallmarks of Alzheimer’s disease, like the telltale plaques and tangles that riddle the brain. Then they crosschecked this data with information from people’s activity trackers.They found a strong relationship between being in motion and healthy microglia, especially in portions of the brain involved in memory. Microglia from the most active elderly men and women contained biochemical markers indicating the cells knew how to be quiet when needed. But microglia from sedentary participants showed signs of having become stuck in unhealthy overdrive during their final years. Those inactive men and women also generally scored lowest on cognitive tests.Perhaps most interesting, though, these effects were greatest in people whose brains showed signs of Alzheimer’s disease when they died, regardless of whether they had serious memory impairments while they were still alive. If these people had been inactive, their microglia tended to look quite dysfunctional, and their memories tended to be spotty. But if people frequently had moved around during late life, their microglia usually appeared healthy after their deaths, and many had not experienced notable memory loss in their later years. Their brains may have showed signs of Alzheimer’s, but their lives and thinking abilities had not.What these findings suggest is that physical activity may delay or alter memory loss from Alzheimer’s disease in older people, partly by keeping microglia fit, said Kaitlin Casaletto, an assistant professor of neuropsychology at the U.C.S.F. Memory and Aging Center, who led the new study.Encouragingly, the amount of activity needed to see these benefits was not large, Dr. Casaletto said. None of the participants had been running marathons in their twilight years. Few had formally exercised. “But there was a linear relationship” between how still they were and their brain health, she said. “The less they sat, the more they stood, the more they moved around, the better their outcomes.”The study is important, said Mark Gluck, a professor of neuroscience at Rutgers University in New Jersey, who was not involved in the research. The findings are “the first to use post-mortem analyses of brain tissue to show that a marker of inflammation in the brain, microglial activation, appears to be the mechanism through which physical activity can reduce brain inflammation and help protect against the cognitive ravages of Alzheimer’s disease,” he said, though further research in living people is needed.In addition, no one believes microglia are the only aspect of the brain affected by movement, Dr. Casaletto said. Physical activity changes countless other cells, genes and chemicals in the brain, she said, and some of those effects may be more important than microglia in keeping us mentally sharp. This study also does not prove activity causes microglia to work better, only that healthy microglia are common in people who are active. Finally, it does not tell us whether we get extra brain benefits from being physically active when we are far younger than 80-plus. But Dr. Casaletto, who is 36, said the study’s results keep her exercising.

For most of us, exercise impacts our hunger and weight in unexpected and sometimes contradictory ways.Does being active make us ravenous afterward and prone to eating more than we perhaps should? Or does it blunt our appetites and make it easier for us to skip that last, tempting slice of pie?A new study provides timely, if cautionary, clues. The study, which involved overweight, sedentary men and women and several types of moderate exercise, found that people who worked out did not overeat afterward at an enticing buffet lunch. However, they also did not skip dessert or skimp on portions. The findings offer a reminder during the holidays that while exercise has countless health benefits, helping us eat less or lose weight may not be among them.For most of us, exercise affects our weight and hunger in unexpected and sometimes contradictory ways. According to multiple scientific studies, few people who start to exercise drop as many pounds as the number of calories they burn working out would foretell.Some recent research suggests this occurs because our bodies stubbornly try to hang on to our fat stores, an evolutionary adaptation that protects us against (unlikely) future famines. So, if we burn calories during exercise, our bodies might nudge us to sit more afterward or reallocate energy from some bodily systems to others, reducing our overall daily energy expenditure. In this way, our bodies unconsciously compensate for many of the calories we burn exercising, reducing our chances of dropping pounds by working out.But that caloric compensation happens slowly, over the course of weeks or months, and involves energy expenditure. It has been less clear whether and how exercise influences our energy intake — that is, how many servings of food we consume — especially in the hours immediately after a workout.The evidence so far has been mixed. Some studies indicate that exercise, especially if it is strenuous and prolonged, tends to blunt people’s appetites, often for hours or into the next day. This phenomenon prompts them to take in fewer calories at subsequent meals than they would had they not exercised. But other studies suggest the opposite, finding that some people feel hungrier after workouts of any kind, and soon replace the calories they expended — and then some — with an extra helping or two at their next meal.Many of those studies, though, relied on healthy, fit and active young men and women as subjects, since those groups tend to be in ready supply among students in exercise science departments at universities. Fewer experiments have looked at how exercise might immediately affect appetite and eating in older, overweight, sedentary adults, and even fewer have studied the effects of resistance training as well as aerobic exercise.The new study was published in October in Medicine & Science in Sports & Exercise. Scientists at the University of Utah in Salt Lake City, the University of Colorado Anschutz Medical Campus in Aurora and other institutions advertised for volunteers in Colorado willing to exercise and eat, for the sake of science.Winnowing hundreds of replies, they wound up with 24 men and women, ranging in age from 18 to 55, who were overweight or obese and generally inactive. They invited everyone to visit the lab first thing in the morning, fed them breakfast, and then, on separate days, had them sit quietly, walk briskly on a treadmill or lift weights for about 45 minutes.Before, during and for three hours afterward, the researchers drew blood to check for changes in hormones related to appetite and asked people how hungry they felt. They also let everyone help themselves to an open buffet lunch of lasagna, salad, rolls, soda and poundcake with strawberries, while unobtrusively monitoring how much food people consumed.Then the researchers compared hormones, hunger and actual eating and found odd disconnects. In general, people’s hormones shifted after each exercise session in ways that could be expected to reduce their appetites. But the study’s participants did not report feeling less hungry — nor did they report feeling hungrier — after their workouts compared with when they had sat. And at lunch, they ate about the same amount, about 950 calories worth of lasagna and the other buffet foods, whether they worked out or not.The upshot of these results suggests that, at the very least, brisk walking or light weight lifting may not affect our subsequent eating as much as “other factors,” such as the aroma and oozing gustatory delights of lasagna (or buttery rolls or pie), said Tanya Halliday, an assistant professor of health and kinesiology at the University of Utah, who led the new study. People’s appetite hormones may have dropped a bit after their workouts, but those drops did not have much effect on how much they ate afterward.Still, exercise burned some calories, she said — about 300 or so each session. That was less than the nearly 1,000 calories the volunteers consumed on average at lunch, but hundreds more than when they sat. Over time, this difference might help with weight control, she said.Of course, the study has obvious limitations. It looked at a single session of moderate, brief exercise by a couple dozen out-of-shape participants. People who work out regularly, or who do more strenuous workouts, might respond differently. Researchers will need to conduct more studies, including those with more diverse groups and those that take place over a longer time period.But even now, the findings have a gentle, apple-pie allure. They suggest “people shouldn’t be afraid that if they exercise, they will overeat,” Dr. Halliday said. And, she said, “Thanksgiving is just one day” and will not affect your weight in the long term. So, eat what you want at the feast and enjoy. Dr. Halliday also recommended going for a walk or join a Turkey Trot with your family and friends beforehand, if you can — not to blunt your appetite, but to boost your social bonds and to be thankful to be moving forward together.

More than 46,000 cancers in America each year, or about 3 percent of cases, could be prevented by meeting physical activity guidelines.More than 46,000 cancer cases in the United States might be prevented each year if almost all of us walked for about 45 minutes a day, according to an eye-opening new study of inactivity, exercise and malignancies. The study, which analyzed cancer incidence and the physical activity habits of nearly 600,000 American men and women in every state and the District of Columbia, found that about 3 percent of common cancers in the United States are strongly linked to inactivity. Something as simple as getting up and moving, the findings suggest, might help tens of thousands of us avoid developing cancer in the coming years.Already we have plenty of evidence that exercise affects cancer risk. In past experiments, physical activity has changed the immune system in ways that amplify the body’s ability to fight tumor growth. Exercise can, for example, ramp up the activity of certain immune cells known to target cancer cells. Exercise has also been associated with longer survival in people with certain forms of cancer, possibly by boosting levels of inflammatory substances that inhibit cancer cell growth. A 2016 review in JAMA Internal Medicine concluded that our risks for at least 13 types of cancer, including breast, bladder, blood and rectal cancers, drop substantially if we are physically active, and a separate 2019 report calculated that those reductions could be as high as 69 percent. At the same time, many studies show that being inactive raises our risks for various cancers. But scientists know surprisingly little about how those risks translate into actual cases or, more concretely, how many people each year are likely to develop cancers closely linked to moving too little.So, for the new study, which was published in October in Medicine & Science in Sports & Exercise, researchers with the American Cancer Society and Emory University in Atlanta used a sophisticated type of statistical analysis called P.A.F. to measure the links between cancer and inactivity. P.A.F. stands for population-attributable fraction and is a mathematical way for scientists to estimate how many occurrences of a disease — or drug responses or other biological reactions — within a larger population seem to be the result of a particular behavior or other factor. It can tell us, in essence, how many annual cases of, say, colon cancer — out of all the known instances of the disease each year — can reasonably be laid at the feet of smoking or alcohol or fatty foods or over-sitting.To start calculating the P.A.F. of cancer resulting from inactivity, the American Cancer Society scientists first pulled anonymized data from the U.S. Cancer Statistics database about cases, nationally and by state, for all Americans 20 and older between 2013 and 2016. The team focused both on total cancer cases and on seven types of cancer that in past studies had been closely tied in part to activity (or inactivity), which are stomach, kidney, esophageal, colon, bladder, breast and endometrial tumors.Next they checked on how much American adults claim to move, based on more than half a million replies to two large federal surveys. Both ask people in what ways and how often they exercise. The researchers drew responses from adults in every state and grouped them, based on whether or not people met the American Cancer Society recommendations for physical activity. Those guidelines call for, ideally, 300 minutes, or five hours, of moderate exercise, like a brisk walk, every week to reduce cancer risk. Finally, the researchers adjusted these statistics for body mass and other factors, gathered additional data about cancer risks and plugged all of the numbers into an equation, which then spit out the P.A.F. for cancers linked to inactivity. That number turned out to be 46,356, or about 3 percent of all cancers annually (excluding non-melanoma skin cancers). When they then looked at individual types of cancer, stomach cancer was most tied to inactivity, with about 17 percent of all cases annually attributable to not moving, versus 4 percent of bladder cancers. Likewise, the numbers varied by state, rising to nearly 4 percent of cancers in many Southern states, where residents tend to report getting relatively little exercise, but about 2 percent in much of the Mountain West, which has relatively active populations.The good news, however, is that these numbers are malleable. We have the ability to lower them. Exercise could “potentially prevent many cancers in the United States,” said Adair K. Minihan, an associate scientist at the American Cancer Society, who led the new study. If everyone in America who can exercise started walking for an hour on weekdays, she said, theoretically the 46,356 cases tied to inactivity should disappear.Of course, cancer is a bogglingly complex disease that has many overlapping, entwined causes, with inactivity playing just a small potential role. Furthermore, statistical risks never drop to zero. Many of the most active people can and do develop cancer, Ms. Minihan pointed out.This study, she emphasized, is not meant “to shame people for not exercising,” or suggest someone’s tumor is his or her fault for skipping the gym sometimes. “There are so many obstacles” to exercise, she said, and so many factors that go into who ultimately develops cancer. But the results do intimate that if each of us could find a way to fit in 45 minutes a day or so of simple exercise, like walking, we might reshape our odds of developing many types of malignancies.

What you need to know about high-intensity interval training, or HIIT.For the past five years or so, high-intensity interval training, or HIIT, has been one of the most popular and controversial forms of exercise. Consisting of brief spurts of intense exercise interspersed with rest, various versions of HIIT have been tested, tried, talked about and sometimes derided by countless researchers, coaches, journalists, influencers and almost anyone else interested in fitness. Gym franchises and online classes specialize in HIIT. Dozens of scientific studies every month explore its benefits and drawbacks. By almost any measure, HIIT is hot.But plenty of questions remain about HIIT. Is it particularly good for our hearts? Minds? Life spans? Waistlines? Is it better for us, long term, than taking a brisk daily stroll? And what does “intense” exercise even mean?With New Year’s exercise resolutions almost around the corner, now seems the right moment to home in on HIIT, and how and why to try it. It is also useful to explore the best way to do HIIT, as well as whether we need a pricey heart rate monitor, gym membership, personal trainer and advanced math skills to get started, or if sneakers, a handy hill and a distant tree can be equipment enough.What is HIIT?With HIIT, you strenuously ride, run, swim, hop, crunch or otherwise push yourself aerobically for a few minutes or even seconds, slow or stop to rest for a few more minutes, and repeat that sequence three or four times, or more. The aim is to “challenge” your cardiovascular system and muscles during each interval, without tipping yourself into abject exhaustion or injury, said Martin Gibala, a professor at McMaster University in Hamilton, Ontario, and prominent HIIT researcher. Alluringly, HIIT workouts can be quite brief, often requiring fewer than 10 minutes in total to complete.This exercise approach is not new, of course. Athletes looking for performance boosts have threaded interval sessions into their broader training since time immemorial. But today’s HIIT is often promoted as the only exercise you have to do — and not an add-on to other, longer, moderate sessions.Does HIIT work?“For most people, there is no doubt that HIIT leads to larger increases in VO2max” — or maximal oxygen uptake, a measure of our aerobic fitness and endurance — “than exercise of a more moderate nature,” said Ulrik Wisloff, a professor and head of the cardiac exercise research group at the Norwegian University of Science and Technology in Trondheim, who has been studying HIIT for more than 20 years. A higher VO2max is strongly associated with greater longevity, he added, suggesting intervals are likely to have a more potent influence on our life spans than, for instance, gentle walks.HIIT also may help to reduce fat stores around our midsections as effectively as longer, easier exercise, and it seems uniquely beneficial for our brains. “HIIT improves memory in younger and older adults,” in ways that standard, moderate exercise cannot, said Jennifer Heisz, a professor at McMaster University and the author of the upcoming book “Move the Body, Heal the Mind,” which will be published in March. Only strenuous exercise prompts the muscles to produce a gush of the chemical lactate, she said, which then travels through the blood to the brain, where it is known to promote the creation of new cells and blood vessels, upping brain health and lowering our risk for dementia.Most beguiling, HIIT workouts can be exceptionally brief. In a famous 2006 study from Dr. Gibala’s lab, for two weeks one group of college students pedaled stationary bicycles moderately for 90 to 120 minutes, three times a week, while another group grunted through four to six sessions of 30 seconds of all-out cycling followed by four minutes of recovery. The moderate exercisers, who topped out at about 12 hours of exercise altogether, showed improved measures of fitness and healthfully remodeled the inner workings of their muscle cells. But the HIIT riders, who completed 12 total minutes of intense exercise, grew just as fit or fitter and showed even more molecular alterations inside their muscles.Where HIIT falls short.“It is neither practical nor advisable to be doing HIIT on a daily basis,” said Jamie Burr, a professor at the University of Guelph in Ontario, who has studied the physiological effects of many types of physical activity. Health guidelines generally advise against this kind of exercise more than three times a week, he said, to avoid burnout or injury.But in that case, we are not exercising for at least four days of the week, which can be problematic. “There are a number of health benefits,” most of them related to better blood sugar and blood pressure levels, he said, that occur only on days when we exercise. When we skip working out, even if we did HIIT the day before, our blood sugar and blood pressure control may slip, undercutting the long-term metabolic gains from those earlier intervals. So, if you decide to do HIIT, plan to schedule other types of exercise, he said, such as moderate walking, cycling, swimming, jogging or calisthenics on most other days of the week.IT rather than HIIT?Perhaps the biggest impediment to HIIT for many people, though, is that name.“I wish we would start using the more-encompassing term ‘interval training,’” rather than HIIT, Dr. Gibala said. “So many people are intimidated, because they think HIIT has to be this all-out, hard-as-you-can-go, gut-busting workout.” It does not, he said. On a green-yellow-red spectrum of physical effort, he said, it is “yellow.”“You should be able to have short conversations with another person” during a typical interval, Dr. Wisloff said. “But if that person asks you to sing, you should not be able to.”In practice, this level of effort could mean walking up a hill instead of on level ground, Dr. Wisloff said. Interval walking, in fact, can be an ideal introduction to this kind of exercise. In a large-scale experiment a few years ago in Japan, almost 700 middle-aged and older adults walked for 30 minutes, some at their usual pace, while others alternated three minutes of up-tempo walking with three minutes of strolling. At the end of five months, the interval walkers were considerably fitter and stronger than the others. And when the researchers checked back in with the volunteers two years later, 70 percent of the interval walkers were voluntarily continuing with their interval program.Keep it simple. Consider fartleks.Interested in trying HIIT now? Good, Dr. Wisloff said. “I would say that everyone should aim for at least one HIIT session per week, for the sake of health,” he said.Choose whichever variety of HIIT appeals to you. You might try one minute on, one minute off, meaning you push yourself for 60 seconds, rest for 60, and repeat, or the four-minute interval workouts employed often in Dr. Wisloff’s research, with four minutes of strenuous effort followed by four minutes of rest. Other researchers use four-second intervals, and I have tried and enjoyed the 10-20-30 approach, which was pioneered by scientists in Copenhagen, during which you jog or otherwise exercise gently for 30 seconds, ramp up the effort for 20 seconds and then sprint for 10 seconds, before returning to the easy half-minute jog.But lately, I have settled into frequent fartleks. Swedish for speed play, fartlek workouts involve picking a goal, such as a tree or light pole up ahead, and speeding up until you reach it. No need to check your heart rate or track each interval’s length, in time or distance, said Dr. Wisloff, who also trains with fartlek. Use the natural contours of the landscape to shape your exercise. “This is perfect to do outside the gym,” he said, with little expense or experience needed. Just dash toward the tree until it recedes behind you, pick another landmark ahead, and you’ll be “HIITing” health and fitness goals.

Twenty minutes of cycling may prime muscles in the arms to grow more while lifting.Riding or running before you lift weights could amplify the effects of the lifting, according to a helpful new study of the molecular impacts of combining endurance and resistance exercise in a single workout. The study, which involved eight physically active men, found that 20 minutes of intense cycling right before an upper-body weight routine alters the inner workings of muscles, priming them to change and grow more than with lifting alone. The new paper, published in Scientific Reports, offers practical guidance about how you might structure a gym workout for maximal benefit. It is also a bracing reminder of how potent and wide-ranging the effects of exercise may be.For decades, trainers and scientists have debated whether and how to mix cardio and resistance exercise. Some small studies suggest combining the two might up the likely gains from each, especially the resistance training. (Almost all of these experiments have been conducted in men.) But other research indicates sweaty aerobic workouts beforehand could reduce strength improvements from lifting. The authors of some of these studies speculate that molecular changes within muscles, caused by riding or running, wind up hindering some of the other desirable outcomes from lifting, an effect called exercise interference. Muscle fatigue might also play a role since, in most studies that pair cardio and resistance, volunteers exercise only their lower bodies, using their legs both for the endurance and strength training. Tired from the endurance work, the thinking goes, their leg muscles could have become unable to respond ideally to resistance training.But what if the two types of exercise targeted completely separate groups of muscles, such as legs during the cycling and arms during the weight routine? That was the scenario posed by Marcus Moberg, a professor at the Swedish School of Sport and Health Sciences in Stockholm, who studies muscle health, exercise and metabolism. In that case, would the lower-body endurance exercise augment the benefits of the upper-body weight training? Or would exerting your legs and lungs have zero — or even an unwelcome, counterproductive — impact on the muscles in your arms?To learn more, he and his collaborators recruited eight active adult men in Stockholm and invited them to the lab for measures of their current aerobic fitness and strength. Then, after the men had familiarized themselves with the lab’s workout equipment, the researchers asked them, on a separate visit, to complete a two-part workout.The men began with intense interval cycling. During this endurance exercise, the men pedaled hard for four minutes, rested for three and repeated that sequence five times. After a few minutes of rest, they next moved on to upper-body weight machines that strenuously worked their arm and shoulder muscles.During a different lab visit, the men completed the same weight routine, but with no cycling first.The researchers drew blood and took tiny tissue samples from the men’s triceps muscles before, immediately after, 90 minutes later and then three hours after each workout. (The primary reason women were not included in the study, Dr. Moberg said, was that women’s less-developed triceps muscles make such repeated biopsies difficult and possibly injurious.)Finally, the scientists microscopically examined the men’s blood and muscle samples, looking for substances that indicated how their muscles were responding to the workouts, with special emphasis on proteins and markers of gene activity believed to influence endurance and muscle mass.They found them. After their solo weight training session, the men’s muscles teemed with proteins and genetic markers known to help initiate muscle growth. Those same substances also abounded after the workout that included cycling but were joined by other proteins and gene activity associated with improved endurance.In effect, after the dual workout, the men’s muscles seemed primed to increase in both size and stamina, with no evidence that cycling had interfered, at a molecular level, with lifting. Instead, the aerobic exercise appeared to have broadened and intensified the expected benefits from weight training.“The most fascinating finding is that some biochemical factors evoked by the leg endurance exercise entered the bloodstream and were then able to influence processes in a completely different group of muscles, and in a way that seems to be beneficial for the training adaptations in the arms,” Dr. Moberg said. “It is almost like the endurance exercise performed by the legs was being transferred to some degree to the arms.” He pointed out, too, that the men lifted the same amount of weight during both arm workouts. Hard pedaling with their legs had not tired their arms.“The paper is great,” said Dr. Michael Joyner, a physiologist and anesthesiologist at the Mayo Clinic in Rochester, Minn, who was not involved in the study. Its finding, he added, that “legs might have primed greater activation of key molecular pathways in the arms is a real piece of brain candy.”Of course, this study, like so many similar experiments, involved only men. “But there is no good rationale for believing the effects would be any different in women,” Dr. Moberg said, adding he and his colleagues hope to include women in upcoming experiments with fewer biopsies. This study also was short term and looked at endurance exercise preceding weight training, and not the reverse. Some past experiments suggest lifting first has little impact, for better or worse, on aerobic exercise afterward. But those studies focused on legs, so it remains to be seen if working your arms before cardio can be as worthwhile as the other way around. But over all, the upshot of the findings, Dr. Moberg said, is that starting a workout by exercising your legs and lungs before moving to upper body lifting makes practical and physiological sense. “It can be a time-effective and potentially beneficial approach,” he said.

A study in mice raises intriguing questions about the ways that hormones influence the brain and motivate the body to move.Estrogen may change brain activity in ways that could affect how physically active we are, according to a remarkable new study in mice that looked at DNA, hormones and brain cells. Using advanced technology to pinpoint and reprogram specific genes and neurons in living animals, the study found that surges of estrogen jump-started processes in the mouse brain that prompted the animals — even males — to become more active.The study, which was published recently in Nature, involved mice. While humans share many of the same relevant hormones, genes and neurons, we are not mice and cannot yet say whether our brains and physiological systems work the same way. But the findings may open intriguing avenues of inquiry into why women so often become inactive after menopause, when estrogen fades. The results also underscore how the brain and internal biological processes work together to play an unexpected and substantial role in whether the body gets up and moves or remains mostly still.Moving and matingFor close to a century, since a famous 1924 study involving rats, scientists have known that female mammals tend to be most physically active just before they ovulate, when they are also most sexually receptive. This behavior makes evolutionary sense, since female animals presumably need to be on the hunt then for a mate. In the intervening decades, researchers began to speculate that estrogen must play a driving role in this behavior, with subsequent studies indicating that female lab animals’ daily skitterings typically would surge and wane in tandem with their estrogen levels. But how could estrogen, which primarily controls ovulation and other aspects of reproduction, influence physical activity? That physiological puzzle recently drew the attention of Holly Ingraham, the Herzstein Endowed Professor of Physiology at the University of California, San Francisco, who has a longstanding research interest in women’s physiology and metabolism. She and her collaborators wondered if estrogen might somehow shape genetic activity in the brain, which would then activate brain cells in ways that could set in motion, well, motion itself.To investigate that possibility, the scientists first gathered a crowd of healthy adult female mice and chemically blocked estrogen uptake in some of them, while tracking how much all of the animals moved. Almost immediately, the animals without estrogen became noticeably more sedentary than the other females, confirming that estrogen somehow affects physical activity.Finding the movement cellsNext, the researchers examined the activity of a number of genes in the animals’ brains, noting that one, in particular, enthusiastically pumped out extra proteins when the animals’ brains were bathed in estrogen but became almost quiet when estrogen was absent. This gene, melanocortin-4, or Mc4r, previously had been linked in people to food intake and regulation of body weight. But the scientists now guessed it might also be the bridge between estrogen and the impulse to be physically active, an idea they substantiated by using high-tech genetic mapping techniques refined by one of the study’s authors, Jessica Tollkuhn, an assistant professor at Cold Spring Harbor Laboratory School of Biological Sciences in Cold Spring Harbor, N.Y.These techniques showed, in real time, estrogen binding to Mc4r genes in certain neurons, especially those in a part of the mouse brain involved in energy expenditure. These brain cells also shared connections with other neurons elsewhere in the brain that control the speed at which animals move. Taken together, this experiment showed estrogen firing up a particular gene that turns on certain brain cells that then should be expected to nudge an animal to move.But the scientists had not yet seen these genes and neurons in action, so, as a final aspect of the study, they used a sophisticated technique known as chemogenetics to directly galvanize the relevant neurons in female mice that had been bred to produce no estrogen. Once physically sluggish, these mice now explored, stood, played and ran far more than they had before.Similarly, when the scientists used a form of the gene-editing technology CRISPR to gin up activity of the Mc4r gene in female animals’ brains, the mice became almost twice as active as before, a physical surge that persisted for weeks. Even male mice moved more when their Mc4r gene activity was dialed up by CRISPR, although not as much as the peripatetic females.These results highlight the “complexity of physical activity behavior,” Dr. Ingraham said, and how the willingness to spontaneously move — or not — for any animal likely involves an intricate interplay between genetics, endocrinology and neurology, along with conscious deliberation.The study also raises the intriguing possibility that the “timing of exercise, to have its most beneficial impact for women, might be fine-tuned by considering the changing hormonal milieu,” including the hormonal changes of menopause, said Dr. Tamas Horvath, a professor of neuroscience and obstetrics, gynecology and reproductive sciences at the Yale School of Medicine and chairman of the school’s department of comparative medicine. “Of course, all these observations in mice need to be confirmed to operate in us, humans,” said Dr. Horvath, who was not involved in the current research. “However, the fact that this mechanism is found in an ancient part of the brain suggests that it will be applicable for most mammals, including humans.”‘Knowledge is power’Dr. Ingraham agreed. “We assume this circuit is working in humans, too,” she said and, if so, the new study and any subsequent, related research could help to explain, in part, why inactivity is so common in women after menopause and also offer some potential strategies for overcoming the pull toward lassitude. Increasing estrogen levels in older women, for instance, might, in theory, encourage more movement, though estrogen replacement therapy remains a complicated subject because of heightened cancer risks and other health concerns. The study does hint, however, that it could, eventually, be possible to bypass estrogen and recreate its effects with new therapies that would directly target the Mc4r gene or the relevant neurons in people’s brains and mimic the effects of estrogen without the hormone itself. Any such medical advances are years in the future, Dr. Ingraham said.Already, though, by delving into “the interrelationship between hormones and physical activity in females, this study has significant implications for human research studying the menstrual cycle and hormonal contraceptives and also menopause,” said Paul Ansdel, a lecturer in exercise physiology at Northumbria University in England, who was not involved with the study but has extensively studied menstruation and physical performance. “We know the importance of exercising in later life for promoting and maintaining health,” he continued, “so the challenge for us now is to understand the best ways to stay active throughout the major hormonal transition that is menopause.”“Knowledge is power,” Dr. Ingraham concluded. She noted that because so many of us are living longer now, better understanding of why — and whether — we choose to move can help make those years healthier. For example, knowing that biology might angle us toward the couch if we are women and aging, we could use fitness trackers or training diaries to help us compare our activities from year to year. Or, just honestly assess whether we are as active now as we would like to be, whatever our age (or gender). The brain is a complex organ and our motivations for exercise varied and deep, but we always have the option “to decide to be active,” Dr. Ingraham said, to make the choice to get up and move.

Focusing on external sights and sounds, rather than what’s going on in your body, made running feel easier and improved performance.To make running seem easier, try paying attention to anything other than your body. That’s according to a fascinating new study of the ways in which how we focus as we move can affect how we feel as we move. The study was small and involved novice female runners, but the findings suggest that the more closely runners listen to their bodies, the more draining their running can become, both physically and psychologically. Conversely, the more runners distract themselves from what their bodies are doing as they put one foot in front of the other, the more effortless their run may feel, and the better their performance. These findings could be useful for the many runners about to toe the line at a fall marathon or other race. The results could have implications, too, for any of us who might wonder how to make our workouts feel as tolerable as they possibly can be.Exercise is not always boundless fun, as most of us know from experience. It can be physically unsettling as we begin to move and our heart rates and breathing quicken and muscles start to whinge. It has not been altogether clear, however, how best to cope with these discomforts, so that we can stay motivated to eventually become better at our chosen sport or activity.Many coaches and other authorities, including training partners and friends, will tell you to pay attention to what is going on inside of you, and to focus on the physics of your body, including your form and technique. Listen to your breathing as you move, you may have been told, or count your steps each minute, or think about the process of lifting your knee with each stride.But some research with athletes suggests that paying close attention to your body and its mechanisms may be the wrong way to make moving feel easier and make you better at your sport. In a much-cited 2003 study, for example, skilled golfers putted more adroitly if they did not think about how to putt than when they did, while expert soccer players dribbled effortlessly through cones when their minds wandered, but tended to bobble the ball if they paid attention to their footwork. (People new to soccer, though, dribbled better when they thought about what they were doing, presumably because they did not yet know how to dribble.) These results generally align with a widely held theory in exercise science known as the Constrained Action Hypothesis. It suggests our bodies know how to move better than our conscious minds do. The more we concentrate on or consciously tell our bodies what to do, this theory suggests, the less fluid and efficient our movement becomes.This idea has been borne out in other studies with people practicing a variety of activities. In a 2017 study, for instance, 44 volunteers jumped farther during a standing long jump when they focused on where to land, rather than the correct techniques for leaping, Similarly, in a 2011 study of weight training, 27 men and women activated their arm muscles more fully during biceps curls — meaning their workout was more effective — when they did not think about how to heft the weight than when they did. And in a 2015 study of competitive rowers, the 15 athletes rowed more efficiently when they let their minds attend to almost anything other than how their legs felt as they rowed. Whether a similar dynamic might play out in endurance sports, like distance running, has been mostly unknown, though. So, for the new study, which was published this month in the Journal of Motor Learning and Development, researchers at the University of Tennessee in Knoxville and Shahid Beheshti University in Tehran, Iran, decided to see whether runners would perform more effectively if they were distracted, compared to if they tuned in to what was happening with their bodies.They began by recruiting about a dozen young women. (The research took place in Iran, where studies with volunteers of both genders are discouraged, so no male runners participated.) The women were healthy, active and familiar with running, although none ran regularly. The researchers invited the women to their lab to check everyone’s fitness and top treadmill running speed.Then on subsequent lab visits, the women ran for six minutes at a time, running at about 70 percent of their top speed, while the scientists monitored their oxygen consumption, the amount of lactate in their bloodstreams and their feelings about the difficulty of each run. During one of these sessions, the women fixated intently on the muscles in their feet, as a way to turn their attention inward. During another, they counted steps, so their focus, while still on their body, was broader and more external. In a third run, they counted backward by threes, taking their minds off their bodies but not out of their heads. And finally, in a fourth session, they watched a video of a basketball game, a blunt distraction that pulled their attention completely away from running.When the scientists then compared the women’s physical and emotional reactions to each run, they found that video watching easily bested body listening. The women consumed the least oxygen and produced the least lactate when they viewed basketball and were the most distracted. Their running, physiologically, was least taxing then. They also told the researchers that when they watched the videos, they felt the least strained. Their running felt hardest, on the other hand, when they paid attention to their muscles, with the other strategies falling in between.In essence, the worst strategy for the runners was “thinking about their movements,” said Jared Porter, a professor of human movement at the University of Tennessee, who oversaw the new study. A much better option was to think of something — anything — else.As is typical of exercise science, this study was small, and the Constrained Action Hypothesis remains only a theory. But as the current findings suggest, distractions are likely to make our running more pleasant and probably faster, Dr. Porter said. So, don headphones and stream music or podcasts (while still monitoring the human and vehicular traffic around you for safety, of course). Listen to birdsong or drink in the landscape as you run outdoors, or watch television as you jog on a treadmill.“We were surprised by how significant the effects were” when people’s minds drifted away from their bodies, he said.Many factors no doubt go into how effectively we perform in a sport and how much we might enjoy our workouts. This study looked at brief bouts of running by young, inexperienced female runners. It cannot tell us if the results apply equally to men, older people, longtime runners or people in other endurance sports, like cycling and swimming. “But there is no scientific reason to think they don’t,” Dr. Porter said.

People typically lower their risks of heart disease and premature death far more by gaining fitness than by dropping weight.For better health and a longer life span, exercise is more important than weight loss, especially if you are overweight or obese, according to an interesting new review of the relationships between fitness, weight, heart health and longevity. The study, which analyzed the results of hundreds of previous studies of weight loss and workouts in men and women, found that obese people typically lower their risks of heart disease and premature death far more by gaining fitness than by dropping weight or dieting.The review adds to mounting evidence that most of us can be healthy at any weight, if we are also active enough.I have written frequently in this column about the science of exercise and weight loss, much of which is, frankly, dispiriting, if your goal is to be thinner. This past research overwhelmingly shows that people who start to exercise rarely lose much, if any, weight, unless they also cut back substantially on food intake. Exercise simply burns too few calories, in general, to aid in weight reduction. We also tend to compensate for some portion of the meager caloric outlay from exercise by eating more afterward or moving less or unconsciously dialing back on our bodies’ metabolic operations to reduce overall daily energy expenditure, as I wrote about in last week’s column. Glenn Gaesser, a professor of exercise physiology at Arizona State University in Phoenix, is well versed in the inadequacies of workouts for fat loss. For decades, he has been studying the effects of physical activity on people’s body compositions and metabolisms, as well as their endurance, with a particular focus on people who are obese. Much of his past research has underscored the futility of workouts for weight loss. In a 2015 experiment he oversaw, for instance, 81 sedentary, overweight women began a new routine of walking three times a week for 30 minutes. After 12 weeks, a few of them had shed some body fat, but 55 of them had gained weight.In other studies from Dr. Gaesser’s lab, though, overweight and obese people with significant health problems, including high blood pressure, poor cholesterol profiles or insulin resistance, a marker for Type 2 diabetes, showed considerable improvements in those conditions after they started exercising, whether they dropped any weight or not. Seeing these results, Dr. Gaesser began to wonder if fitness might enable overweight people to enjoy sound metabolic health, whatever their body mass numbers, and potentially live just as long as thinner people — or even longer, if the slender people happened to be out of shape.So, for the new study, which was published this month in iScience, he and his colleague Siddhartha Angadi, a professor of education and kinesiology at the University of Virginia in Charlottesville, began scouring research databases for past studies related to dieting, exercise, fitness, metabolic health and longevity. They were especially interested in meta-analyses, which pool and analyze data from multiple past studies, allowing researchers to look at results from far more people than in most individual studies of weight loss or exercise, which tend to be small-scale.They wound up with more than 200 relevant meta-analyses and individual studies. Then they set out to see what all of this research, involving tens of thousands of men and women, most of them obese, indicated about the relative benefits of losing weight or getting fit for improving metabolisms and longevity. In effect, they asked whether someone who is heavy gets more health bang from losing weight or getting up and moving.The contest, they found, was not close. “Compared head-to-head, the magnitude of benefit was far greater from improving fitness than from losing weight,” Dr. Gaesser said.As a whole, the studies they cite show that sedentary, obese men and women who begin to exercise and improve their fitness can lower their risk of premature death by as much as 30 percent or more, even if their weight does not budge. This improvement generally puts them at lower risk of early death than people who are considered to be of normal weight but out of shape, Dr. Gaesser said.On the other hand, if heavy people lose weight by dieting (not illness), their statistical risk of dying young typically drops by about 16 percent, but not in all studies. Some of the research cited in the new review finds that weight loss among obese people does not decrease mortality risks at all.The new review was not designed to determine precisely how exercise or weight loss affect longevity in people with obesity, though. But in many of the studies they looked at, Dr. Gaesser said, people who shed pounds by dieting regained them, then tried again, a yo-yo approach to weight loss that often contributes to metabolic problems like diabetes and high cholesterol and lower life expectancy.On the other hand, exercise combats those same conditions, he said. It may also, unexpectedly, remake people’s fat stores. “People with obesity usually lose some visceral fat when they exercise,” he said, even if their overall weight loss is negligible. Visceral fat, which collects deep inside our bodies, raises risks for Type 2 diabetes, heart disease and other conditions.A few of the studies they cite find that exercise likewise alters molecular signaling inside other fat cells in ways that may improve insulin resistance, no matter how much weight someone carries. “It looks like exercise makes fat more fit,” Dr. Gaesser said.The primary takeaway of the new review, he concluded, is that you do not need to lose weight to be healthy. “You will be better off, in terms of mortality risk, by increasing your physical activity and fitness than by intentionally losing weight,” he said.