If you’ve eaten something that doesn’t agree with you, your mind probably jumps to your sandwich or the milk in your coffee. As far as food sensitivities go, gluten and lactose are two of the top culprits.

Because food intolerance symptoms often overlap with lactose intolerance and non-celiac gluten sensitivity (or NCGS), it makes it hard to figure out which—if either—is causing digestive distress. “Gastrointestinal issues—such as bloating, gas, problems with bowel movements, abdominal pain, fatigue, and headaches—are common with both,” explains Maxine C. Yeung, RD, founder of The Wellness Whisk.

Whether you try a gluten intolerance test or choose to play detective via your diet, experts agree that there’s no need to rely on wild guesses in an attempt to feel better. I mean, wouldn’t it be great to discover that you don’t really have to ditch pasta or ice cream in the end? Here’s how to get to the bottom of what’s bugging you, from identifying food sensitivities to diagnosing food intolerance.

The difference between lactose intolerance and gluten sensitivity

Even though symptoms can be similar, gluten and lactose sensitivities are quite different.

“Lactose intolerance is fairly straightforward—it occurs when an individual no longer produces the lactase enzyme in sufficient quantities,” says Ryan Whitcomb, MS, RD, CLT, an integrative and functional dietitian and nutritionist. (Many people don’t once childhood ends or they’ve quit dairy for an extended amount of time.) “Lactase is responsible for breaking down lactose, the natural sugar found in dairy products like milk. Since the body is not able to break this sugar down in the small intestine, where it’s supposed to be digested, it moves into the large intestine.” Here, it produces gas, which causes those unpleasant GI symptoms. You may also experience issues like bloat, nausea and vomiting, stomach pain, and diarrhea.

NCGS, on the other hand, isn’t well understood. It can cause the same wide range of symptoms as celiac disease, which, in addition to digestive symptoms, can include things like brain fog, rashes, and joint pain. That’s why the two dietary intolerances are often confused with each other.

“Gluten sensitivity is an immune (non-life-threatening) reaction to ingesting gluten (the protein in wheat, barley, and rye). The tricky part with gluten sensitivity is that reactions can be immediate or occur hours to days later and typically involve various immunoglobulin antibodies,” says Meg Gerber, RD, functional medicine dietitian and founder of Grounded Nourishment. “Celiac disease, on the other hand, is an autoimmune disease in which the body attacks itself in response to eating gluten. Celiac disease has a higher level of associated risk with ingesting gluten, as it can potentially cause lifelong damage to the small intestine and can result in infertility, osteoporosis, and gastrointestinal cancer.”

That means if someone with gluten sensitivity and celiac disease both knowingly eat gluten, “the risks and long-term consequences for someone with celiac disease are overtly higher and more dangerous,” says Gerber.

Wheat allergy vs. gluten sensitivity

Contrary to popular belief, celiac disease isn’t the same thing as a wheat allergy. Celiac is an autoimmune condition, while the Gluten Intolerance Group notes that a wheat allergy “involves an immune (not auto-immune) response.” A wheat allergy is also different from gluten intolerance or gluten sensitivity (two terms that are used interchangeably). While an allergy can be life-threatening, a gluten intolerance typically is not.

Let’s start with gluten and wheat allergies. “A wheat allergy is an adverse immune reaction to gluten that involves IgE antibodies and can trigger a significant immediate histamine reaction leading to hives, throat closure, and/or digestive issues,” says Gerber. According to the American College of Allergy, Asthma & Immunology, gluten allergy symptoms can range from hives or rashes, nausea, stomach cramps, headaches, a stuffy or runny nose, and asthma to anaphylaxis, which is less common but can be life-threatening. By no surprise, the triggers of these gluten allergy symptoms are eating any food containing wheat (such as bread and pasta) or using nonfood items that contain wheat-based ingredients (like certain cosmetics).

While gluten allergy symptoms can sometimes be scary, dietary intolerances aren’t as severe. “Gluten sensitivity is typically much less serious than a true wheat allergy,” says Gerber. “The big difference is the immediacy of the allergy response vs. a sensitivity reaction that’s not always immediate and can be hours/days later.” Gluten intolerance symptoms include abdominal pain, anemia, anxiety, bloating or gas, diarrhea or constipation, headaches, joint pain, and depression.

The cause of food intolerance symptoms still isn’t well understood, but past research has shown fructans, a carbohydrate that’s found in large quantities in wheat, could be causing the problem (rather than the gluten itself).

How to diagnose food intolerances the high-tech way

How does a doctor test for gluten intolerance or lactose intolerance? Intolerance testing options can look a little different, depending on how your specific health pro chooses to investigate a potential gluten and lactose sensitivity.

Let’s start with lactose intolerance testing. In this case, identifying food sensitivities is done through a breath test. “The best test for lactose intolerance is a breath test, of which there are two types: the lactose hydrogen breath test and the hydrogen/methane breath test,” says Whitcomb. These tests can measure how much gas is being produced after the consumption of dairy, and Whitcomb says the latter is more accurate.

Diagnosing food intolerance in the case of NCGS is more difficult. The official diagnosis process is tricky, as there’s currently no reliable blood test for gluten intolerance specifically—just celiac disease. So the first step is ruling celiac out, notes Amy Gorin, MS, RDN, owner of Plant-Based With Amy. “There are blood tests to diagnose celiac disease, and for these tests to be accurate, they must be done while you are consuming a gluten-containing diet,” she says. (So don’t cut out the croissants just yet.) “A biopsy of the small intestine can confirm positive blood-test results.”

It’s worth noting that celiac testing results aren’t always black and white. But if celiac disease and other problems—like a wheat allergy, SIBO, or other intolerances like lactose—have been ruled out, NCGS may be your issue. The only way to know for sure is to see whether you feel better without gluten in your diet. (Gluten-free diet, here you come.)

Many health practitioners’ official diagnosis process for food sensitivities includes the Mediator Release Test (or MRT). It looks at up to 170 foods and chemicals, and while it doesn’t test for gluten intolerance directly, it tests gluten-containing foods like wheat, barley, and rye. But there are some potential issues to keep in mind when diagnosing food intolerance with these types of tests.

“There are a number of food sensitivity blood tests on the market that predominantly look at IgA and IgG antibodies as a marker of an immune response to certain foods. The problem with these tests is that they aren’t well validated in the literature,” says Gerber. “In addition, in my 10 years of experience working with clients (and running these tests in the past), they can often cause undue ‘food fear’ from false positives. It’s possible that these tests can at times yield a false positive due to gut permeability and presence of foods that are often consumed in the diet, not due to a specific true food sensitivity.”

How to test for gluten intolerance at home

Intolerance testing methods aren’t always 100 percent accurate, making the official diagnosis process—and actually uncovering any gluten and lactose sensitivities—really tricky. They can also be very costly. If you’re wondering how to test for gluten intolerance at home, another option is a good old-fashioned elimination diet. Basically, that means you just stop eating iffy foods and see how you feel.

“If you strongly suspect your symptoms may be related to either lactose or gluten, then eliminating the individual categories may be okay,” says Yeung. (That is, just removing gluten and/or lactose.) “If you’re unable to see patterns in the foods you eat and your symptoms, then I’d recommend a full elimination diet,” she says. While elimination diets vary, they often rule out foods like dairy, gluten/wheat, eggs, soy, nightshades, and more.

Unfortunately, this is probably the most time-consuming and restrictive plan of action. But if you’re diving into the challenge, here’s how it usually goes down. “Typically you begin by eliminating all sources that may be causing adverse effects for at least one to two weeks,” says Yeung. “After the initial phase, you begin reintroducing foods from one category at a time while continuing to eliminate the other categories.”

There’s no correct order in which to reintroduce foods—the most important thing is that you test only one food at a time. For example, if you think you may be lactose intolerant and are reintroducing dairy while lactose intolerance testing, you might start with a small amount of milk one day, monitor symptoms in a journal, then try a little more the next day. “If this food is a problem food, you will likely experience symptoms,” says Yeung. Even if you don’t react to it, Yeung recommends repeating the process twice for each food group for max accuracy.

You might find that you feel more tired with gluten in your diet, or that foods made with milk mess with your bathroom habits. Or maybe, you find another result that’s completely unexpected. Yes, the quest to uncover food sensitivities can be tough—but if it comes with a calmer gut or more energy, isn’t that totally worth it?

Frequently asked questions about gluten intolerance

What are the warning signs of gluten intolerance?

According to Gerber, gluten intolerance is often associated with digestive symptoms. When you eat gluten, you may experience “acid reflux, bloating, abdominal pain, gas, constipation, and/or diarrhea,” she says. If you’re looking for a gluten intolerance diagnosis, read up on the intolerance testing options above.

Can you self-diagnose gluten intolerance?

Looking for a gluten intolerance diagnosis? Gerber recommends trying a food elimination diet, which can help with identifying food sensitivities. It’s also a simple way to test for gluten intolerance at home.

“The tried and true gold standard for gluten intolerance or sensitivity is a dietitian-lead food elimination diet so that the client can be guided through the elimination process and provided foods to eat while also being led through the reintroduction phase of the elimination diet,” says Gerber. “Food intolerances are often dose dependent, so reintroducing the foods to identify specific portion sizes that can cause reactions can be beneficial.”

For example, in the case of lactose intolerance testing, Gerber says someone may be able to tolerate small amounts of low-lactose foods like hard cheeses, butter, and yogurt but have diarrhea with a cup of ice cream.

Do gluten digestion pills help with food intolerance symptoms?

You’ve probably seen gluten pills, which are marketed as an easy way to enjoy all the pasta, bread, and cereal you want sans digestive issues. But are they a true fix when you’re trying to manage a gluten intolerance diagnosis? Unfortunately, the pills—which contain a blend of enzymes that are intended to help the body break down gluten—have mixed reviews. One study found the supplements didn’t help, while another found they may improve symptoms in individuals with NCGS.

Experts have opinions, too: “The descriptions of some of the gluten-digesting products state that the ingredients act upon the carbohydrate component of gluten-containing grains,” Julie Stefanski, RDN, a spokesperson for the Academy of Nutrition and Dietetics, previously told Well+Good. “But gluten is a protein, not a carbohydrate—so the ingredients in a supplement may not target the actual source of discomfort.”

All in all, while these pills aren’t a miracle, you can always give them a shot (so long as you check with your doctor before doing so).

Why might someone suddenly be gluten intolerant when they were fine before?

Your body used to handle gluten just fine, but now you’re experiencing digestive issues. So what’s causing the change in your health and food reactions? “Many things can influence the ability of the digestive tract to properly function, including stress, pharmaceutical drugs, consumption of ultra-processed foods, and pesticide exposures,” says Gerber. “Most predominantly, most of the wheat-containing foods sold in the grocery store nowadays are made from an ultra-processed, hybridized form of wheat that is far more difficult to digest than the more ancient variants of the wheat plant.”

If you suspect a gluten sensitivity or intolerance, Gerber says you may be able to tolerate “easier to digest” forms of gluten. “Think sourdough or einkorn wheat vs. packaged and processed forms like wheat crackers and pasta,” she says. If you want to dig deeper into the issue, try utilizing some intolerance testing methods like an elimination diet. That way, you can discover exactly what’s causing issues.

Why am I not lactose intolerant in Europe?

Dealing with digestive distress in the United States, but not lactose intolerant in Europe? There could be a reason for that. Many people have shared how their dietary intolerances are different abroad. While that could be due to the differences between European dairy and American dairy (including the pasteurization methods and additives used), your health and food reactions while abroad could also be due to the different levels of lactose content in what you’re eating, your stress levels, or even portion sizes.