The pandemic has shed a blinding light on too many Americans’ failure to follow the well-established scientific principles of personal health and well-being. There are several reasons this country, one of the world’s richest and most highly developed, has suffered much higher rates of Covid-19 infections and deaths than many poorer and less well-equipped populations.

Older Americans have been particularly hard hit by this novel coronavirus. When cases surged at the end of last year, Covid-19 became the nation’s leading cause of death, deadlier than heart disease and cancer.

But while there’s nothing anyone can do to stop the march of time, several leading risk factors for Covid-19 infections and deaths stem from how many Americans conduct their lives from childhood on and their misguided reliance on medicine to patch up their self-inflicted wounds.

After old age, obesity is the second leading risk factor for death among those who become infected and critically ill with Covid-19. Seventy percent of Americans adults are now overweight, and more than a third are obese. Two other major risks for Covid, Type 2 diabetes and high blood pressure, are most often the result of excess weight, which in turn reflects unhealthy dietary and exercise habits. These conditions may be particularly prevalent in communities of color, who are likewise disproportionately affected by the pandemic.

Several people I know packed on quite a few pounds of health-robbing body fat this past year, and not because they lacked the ability to purchase and consume a more nutritious plant-based diet or to exercise regularly within or outside their homes. One male friend in his 50s unexpectedly qualified for the Covid vaccine by having an underlying health condition when his doctor found he’d become obese since the pandemic began.

A Harris Poll, conducted for the American Psychological Association in late February, revealed that 42 percent of respondents had gained an average of 29 “pandemic pounds,” increasing their Covid risk.

So what can we learn from these trends? Tom Vilsack, the new Secretary of Agriculture, put it bluntly a week ago in Politico Pro’s Morning Agriculture newsletter: “We cannot have the level of obesity. We cannot have the level of diabetes we have. We cannot have the level of chronic disease … It will literally cripple our country.”

Of course, in recent decades many of the policies of the department Mr. Vilsack now heads have contributed mightily to Americans’ access to inexpensive foods that flesh out their bones with unwholesome calories and undermine their health. Two telling examples: The government subsidizes the production of both soybeans and corn, most of which is used to feed livestock.

Not only does livestock production make a major contribution to global warming, much of its output ends up as inexpensive, often highly processed fast foods that can prompt people to overeat and raise their risk of developing heart disease, diabetes, high blood pressure and kidney disease. But there are no subsidies for the kinds of fruits and vegetables that can counter the disorders that render people more vulnerable to the coronavirus.

As Mr. Vilsack said, “The time has come for us to transform the food system in this country in an accelerated way.”

Early in the pandemic, when most businesses and entertainment venues were forced to close, toilet paper was not the only commodity stripped from market shelves. The country was suddenly faced with a shortage of flour and yeast as millions of Americans “stuck” at home went on a baking frenzy. While I understood their need to relieve stress, feel productive and perhaps help others less able or so inclined, bread, muffins and cookies were not the most wholesome products that might have emerged from pandemic kitchens.

When calorie-rich foods and snacks are in the home, they can be hard to resist when there’s little else to prompt the release of pleasure-enhancing brain chemicals. To no one’s great surprise, smoking rates also rose during the pandemic, introducing yet another risk to Covid susceptibility.

And there’s been a run on alcoholic beverages. National sales of alcohol during one week in March 2020 were 54 percent higher than the comparable week the year before. The Harris Poll corroborated that nearly one adult in four drank more alcohol than usual to cope with pandemic-related stress. Not only is alcohol a source of nutritionally empty calories, its wanton consumption can result in reckless behavior that further raises susceptibility to Covid.

Well before the pandemic prompted a rise in calorie consumption, Americans were eating significantly more calories each day than they realized, thanks in large part to the ready availability of ultra-processed foods, especially those that tease, “you can’t eat just one.” (Example: Corn on the cob is unprocessed, canned corn is minimally processed, but Doritos are ultra-processed).

In a brief but carefully designed diet study, Kevin D. Hall and colleagues at the National Institutes of Health surreptitiously gave 20 adults diets that were rich in either ultra-processed foods or unprocessed foods matched for calorie, sugar, fat, sodium, fiber and protein content. Told to eat as much as they wanted, the unsuspecting participants consumed 500 calories a day more on the ultra-processed diet.

If you’ve been reading my column for years, you already know that I’m not a fanatic when it comes to food. I have many containers of ice cream in my freezer; cookies, crackers and even chips in my cupboard; and I enjoy a burger now and then. But my daily diet is based primarily on vegetables, with fish, beans and nonfat milk my main sources of protein. My consumption of snacks and ice cream is portion-controlled and, along with daily exercise, has enabled me to remain weight-stable despite yearlong pandemic stress and occasional despair.

As Marion Nestle, professor emerita of nutrition, food studies and public health at New York University, says, “This is not rocket science.” She does not preach deprivation, only moderation (except perhaps for a total ban on soda). “We need a national policy aimed at preventing obesity,” she told me, “a national campaign to help all Americans get healthier.”