Scientists often debate whether irritable bowel syndrome is a mental or physical issue. That’s not much help for those who suffer from it.The New Mexican desert unrolled on either side of the highway like a canvas spangled at intervals by the smallest of towns. I was on a road trip with my 20-year-old son from our home in Los Angeles to his college in Michigan. Eli, trying to be patient, plowed down I-40 as daylight dimmed and I scrolled through my phone searching for a restaurant or dish that would not cause me pain. After years of carefully navigating dinners out and meals in, it had finally happened: There was nowhere I could eat.“I’m so sorry, honey,” I said. “I feel really, really bad.” And I did. I was on the verge of tears, as much out of self-pity and shame as any maternal concern.Eli shook his head. “It’s OK, Mom. It’s not your fault.”But it was. Because of me — or, to be precise, my digestive system — we would not eat until we reached Amarillo, Texas, at 10 p.m., and bought frozen food from a grocery store near our Airbnb.My gut is not a carefree traveler. Ingest the wrong items, and my stomach feels as though someone’s scoured it with a Brillo pad. For the next few hours, I may also experience migraines, achy joints and a foggy, feverish sensation like I’m coming down with the flu. My doctors call this irritable bowel syndrome, or I.B.S. I call it a terrible shame.I.B.S. is a diagnosis of exclusion, a so-called functional disorder scribbled in your chart only after every test and examination has come back normal. Simply put, there’s nothing wrong with my stomach that our current medical tools can detect. Some physicians and researchers have described this condition in terms of a mind-gut connection.“Everybody has contractions in their gut,” said Dr. Emeran Mayer, a gastroenterologist at the University of California, Los Angeles, and the author of “The Mind-Gut Connection: How the Hidden Conversation Within Our Bodies Impacts Our Mood, Our Choices and Our Overall Health.”The same contractions that go unnoticed by most people cause pain in I.B.S. patients, who have become hypersensitive to sensations in their gut, he said. Calm the mind, the thinking goes, and the gut may follow.Fair or not, I hear this prescription and think, “Oh, so this is all in my head?” Then I fear my stomach aches are my fault, the product of an anxious mind that I cannot tame into submission.That night on the highway, I kept wanting to apologize to my son again. But as Eli flicked on the headlights, I realized he accepted me the way I was. And I wondered, what if I could, too?My I.B.S. journey started about nine years ago, at age 44, when I noticed that my migraines — for decades reliably yoked to my menstrual cycle — were accompanied by a sour stomach, like my gut was sucking on lemons. Cutting out gluten helped, but as the years passed, my gut continued to deteriorate.I later learned my experience is not unusual. Studies suggest that female sex hormones modulate the brain-gut connection, and as these hormones wane, women may experience more severe I.B.S. symptoms.Eventually, I dropped 10 pounds because eating had become so painful. That’s why, in 2015, I landed in the office of a gastroenterologist. He ran a bunch of tests — blood, scopes — and when everything came back negative, he diagnosed me with I.B.S.It could have started with a past infection, he said. Recent stresses in my life probably didn’t help. He had no way of curing me, but he advised me to relax more and manage my diet.If my I.B.S. was triggered by stress, I thought, “I must be the most neurotic person I know.” Thoughts like these did not help me calm down. But that became my new goal: to relax so my belly would no longer hurt.I’d download a new meditation app or try a different therapist or attend restorative yoga classes. My list of restricted foods continued to grow though — no more dairy, soy, alcohol, peanuts, garlic, beans or lentils. I avoided wine and cheese gatherings and scoured the ingredients on packaging and menus. When I stayed off problem foods, my stomach felt better.If I decided I was calmer and began to edge off my strict diet, I’d be miserable again. When I asked Dr. Mayer why no amount of calming would allow me to eat gluten or garlic without pain, he warned me not to underestimate the power of fear.“It’s a very common thing in I.B.S. patients,” he said. He added that an I.B.S. patient’s system “looks at food as a potentially dangerous thing.”Then, this August on that same trip with Eli, I read about a new theory for I.B.S. A paper published in The New England Journal of Medicine theorized that an abdominal infection can temporarily disturb the cell barrier that lines the colon. With the barrier disturbed, allergy-inducing proteins can get absorbed by the colon, triggering localized allergic reactions to certain inflammatory foods like gluten and leading to reverberations up and down the digestive tract.I’d been telling people for years that I didn’t have allergies to certain foods, even though my body’s response to them felt automatic. Now this research seemed to indicate what I was feeling could be an allergic reaction — one no amount of hypnotherapy or journaling was going to make disappear.When I read this, scrolling through my phone at a motel in Illinois, I thought: I knew it. The stabbing stomach pains that woke me at 3 a.m. after eating garlic or black beans weren’t caused by my subconscious; it was my damaged gut.Later, I called Dr. Marc E. Rothenberg, one of the paper’s authors and the director of the division of allergy and immunology at Cincinnati Children’s Hospital Medical Center, to get more clarity.“Stress modifies, and can exacerbate, the underlying disease physiology,” Dr. Rothenberg said. “But stress is not the cause of I.B.S.”There’s an exhaustion that comes from years of trying to make something go away that insists on hanging around. These days, I’m a little less tired from the struggle and a little more at peace with my body. I’ve finally come to the conclusion that suits me: my gut is different than other people’s.From time to time, I still try new remedies to improve digestion or better manage anxiety — a probiotic, Chinese herbs, a new meditation app. But if I’m never able to eat another grilled cheese sandwich (dairy cheese, wheat bread, actual butter), I can live with that. And that’s the most relaxing mantra there is.Constance Sommer is a freelance writer in Los Angeles.