More of us than ever are experiencing stomach trouble or other uncomfortable reactions after we eat. What gives, and what can we do about it?

By Melinda Wenner Moyer
Updated: June 26, 2019
Amy van Luijk

A few months ago, a friend of mine threw a dinner party, only to discover that nearly everyone coming had a food restriction. Gluten, dairy, nuts, sugar, meat: Our cultural food demons seem to grow by the day. According to a 2016 Pew Research Center survey, 32 percent of Americans believe they have at least one food allergy or intolerance—especially women, who are nearly twice as likely to report food allergies as men.

Yet these numbers don’t match official statistics. In 2017, researchers at Harvard Medical School and other institutions analyzed more than 2 million electronic health records and found that only 3.6 percent of adults had doctor-documented food allergies or intolerances. What might explain this bizarre discrepancy? In some cases, of course, people who think they have food sensitivities do not. But another big problem is that the science on how food affects our bodies is still in its infancy. “There’s so much we don’t know,” says professor of gastroenterology and nutrition William Chey, MD, director of the GI Nutrition and Behavioral Health Program at Michigan Medicine at the University of Michigan. Some of these mystery food issues may be real—just misunderstood.

Allergies

More than 170 food ingredients can trigger allergies. The most common are milk, eggs, peanuts, tree nuts, soy, wheat, fish, and shellfish, but you can even be allergic to spices and meat.

When people are exposed to a food they’re allergic to, their immune systems attack the ingredient as if it were a dangerous intruder. The response can be mild—causing, say, a local rash—or it can be life-threatening, thrusting the body into an anaphylactic reaction that thwarts breathing and impedes circulation. Some reactions don’t even involve eating. Stephanie Kokabi, 40, once ended up in the hospital after going to a baseball game. “I was wearing flip-flops, and my feet started swelling up because of the peanuts on the ground,” she recalls. When she struggled to breathe, she was rushed to the ER.

Tests for food allergies aren’t perfect, though, and their limitations explain some of the mismatch between believed and real food sensitivities. Doctors typically diagnose food allergies with skin pricks or blood tests, but positive results don’t necessarily translate into true allergies. “False positive reports from these tests are around 30 to 40 percent,” says Andres Alvarez Pinzon, MD, PhD, clinical research manager at the Sean N. Parker Center for Allergy & Asthma Research at Stanford University. In reality, food allergies are rare, especially among adults (many kids with food allergies eventually grow out of them), but because they are so hard to diagnose, no one knows exactly how many people have them.

Celiac disease

When she was a college freshman in Baltimore, Lauren Taylor, now 28, suddenly felt more exhausted than she ever had before, even though she was sleeping 10 hours a night and taking naps. Her doctor diagnosed her with an iron deficiency, and she started taking supplements (if she missed a dose, she’d feel terrible). Eventually, she required an intravenous iron infusion, which prompted her to seek a second opinion. Her new doctor ran a spate of tests. The diagnosis: celiac disease.

You’ve probably heard of celiac, which afflicts about 1 percent of Americans. It’s an autoimmune disease caused by an abnormal reaction to gluten, a protein found in wheat, rye, barley, and malt. Eating gluten causes sufferers’ immune systems to attack the small intestine, causing damage to the tiny, fingerlike villi that line the intestine and absorb nutrients. Diagnosis usually requires a blood test, endoscopy, and biopsy.

Taylor’s celiac disease inhibited her body’s ability to absorb iron, which is why she felt so tired. But symptoms can include an itchy, blistery rash, stomach pain, gas, joint pain, depression, migraines, and canker sores. Because symptoms are so varied, the Celiac Disease Foundation estimates that 2.5 million Americans have the disease but don’t even know it. If left untreated, the disease can cause serious problems, including infertility and nerve damage. There is no cure, but there is a simple—though not always delicious—method of prevention: avoiding gluten.

The gluten mystery

Celiac isn’t the only reason people avoid gluten. A 2015 Gallup poll found that one in five Americans—many of them not celiac sufferers—eat gluten-free, and the number has likely gone up since.

Why? Many people complain that gluten makes them feel gassy and bloated and causes them to gain weight. But scientists and doctors have had trouble confirming these claims. A handful of factors are likely at play, they say, and gluten may not always be the culprit.

Some people who avoid gluten don’t need to. Several studies suggest that when people just think they’re eating gluten, they believe they feel bad; that’s an example of what experts call the “nocebo effect.” This tendency could in part be due to the fact that gluten has developed such a bad reputation of late.

Still, there are reasons to suspect that gluten-containing foods could cause problems. In a 2016 study, researchers at Columbia University Medical Center and other institutions found that people who said they experienced adverse reactions to wheat but who did not have celiac disease did, nonetheless, have more inflammation and markers of intestinal damage. But gluten may not always be the problem. Wheat also contains tiny carbohydrates that our intestines can’t digest very well and that are known to cause bloating and flatulence. Clinical trials suggest that among patients with irritable bowel syndrome, a condition characterized by bloating, gas, and diarrhea, at least half feel better when they avoid eating some of these carbs, known as FODMAPs (an easier way to say “fermentable oligosaccharides, disaccharides, monosaccharides, and polyols”). Indeed, gastroenterologist Stefano Guandalini, MD, founder of the University of Chicago Celiac Disease Center, says he believes the “vast majority” of people without celiac disease who have stomach issues after eating wheat are reacting to FODMAPs, not gluten.

Most people with FODMAP sensitivity are only reacting to a handful of FODMAPs, so to manage the sensitivity, doctors first try to identify the key culprits. They start by putting sufferers on a diet low in all FODMAPs—cutting out many foods, including garlic, onions, beans, wheat, dairy, and certain fruits—and then slowly add FODMAP sources one at a time to see which ones are causing the problems.

Ultimately, then, “there are multiple reasons why people may develop symptoms and associations after eating wheat, and they’re not mutually exclusive,” says Chey. (To complicate the issue further, it’s also possible to be allergic to certain proteins in wheat other than gluten. Wheat allergies can cause hives, vomiting, and diarrhea.)

Dairy dilemmas

If you feel off after eating dairy, you’re not alone. About 65 percent of adults are lactose intolerant, meaning they don’t produce an enzyme called lactase, which is essential for breaking down the dairy sugar lactose. When lactose isn’t digested, you can experience bloating, gas, and sometimes diarrhea. Yet you don’t have to eschew dairy entirely if you’re lactose intolerant. Hard cheeses and yogurt tend to be low in lactose, so they cause fewer problems. Before you have your first bite of dairy, you can also take an over-the-counter pill, such as Lactaid, which provides the missing digestive enzyme. (Less than 1 percent of adults suffer from true milk allergies, which can cause hives and anaphylaxis.)

Of course, people avoid dairy for other reasons too. Paleo and Whole30 dieters are told to avoid dairy because it supposedly incites inflammation, while keto dieters avoid dairy because of its sugars. “Dairy-free is absolutely trending right now,” says registered dietitian and nutritionist Amy Shapiro, founder of the New York City–based Real Nutrition. But is dairy really inflammatory? According to a 2017 meta-analysis, the opposite is true. Researchers concluded that among people who aren’t allergic, dairy products (especially fermented products, such as yogurt) “have anti-inflammatory properties.” Dairy also provides important nutrients, such as protein, phosphorus, and calcium. Many American women don’t get enough calcium as it is.

Other food enigmas

Doctors know quite a bit about allergies, celiac disease, and dairy intolerance—but there are plenty of food-related issues that physicians are only just starting to figure out. Here’s the thing, says Chey: There are dozens of compounds in any given food, and your gastrointestinal system may handle them differently depending on the substance, time of day, what you ate before them, and whether they’re liquids or solids. “Food is complicated,” he says, so it makes sense that our bodies may have complicated reactions to it. We will need much more research before we get clear answers to many big food questions, but if you’re having weird symptoms after you eat and you don’t know why, find a doctor who will take your concerns seriously. Despite what wellness blogs may suggest, don’t try to make a bunch of dietary changes on your own, warns Guandalini, because you could develop nutritional deficiencies, and you may not succeed in uncovering the root of the problem. As for what kind of doctor to consult, Chey suggests seeing your primary care provider first, who may be able to discern, based on your symptoms, what kind of specialist might be best—a gastroenterologist, allergist, or dietitian, for instance. And if your doctor is utterly dismissive? “That’s a big red flag,” says Chey, a sign it’s time to get another opinion.

Signs and symptoms to look for

Food allergies often cause:

  • Rash or red skin
  • Itchy mouth or ears
  • Nausea, vomiting, diarrhea, or stomach pain
  • Runny nose, sneezing, or cough
  • Trouble swallowing
  • Shortness of breath or chest pain
  • Loss of consciousness

Adult celiac is more likely to cause:

  • Iron-deficiency anemia
  • Fatigue
  • Bone or joint pain or arthritis
  • Osteoporosis
  • Liver and biliary tract disorders
  • Depression or anxiety
  • Tingling, numbness, or pain in the hands and feet
  • Seizures or migraines
  • Missed periods
  • Infertility or recurrent miscarriage
  • Canker sores
  • Itchy, blistery rash
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