Food Intolerance: Five Signs That a Product is Not Right for You

Food intolerance is a reaction of your digestive system. Just like weight loss and fat loss, food intolerance and food allergies sound like the same thing. But they are not.

Although they are often used interchangeably, food intolerance and food allergy are different. According to the Cleveland Clinic, an allergy is your immune system reacting and fighting an ingredient that it mistakenly believes is harmful.

Food intolerance is much more common. A food intolerance is a reaction of your digestive system when you eat or drink something that your body cannot digest.

Bloating and gas

According to Niket Sonpal, MD, an internist and gastroenterologist in New York City, excessive bloating and gas are among the most common symptoms of food intolerance.

After a heavy meal with a high fiber content, you will usually experience mild bloating and gas. But when these symptoms become uncomfortable or painful and occur every time you eat a certain food, they may indicate a food intolerance.

Dr. Sonpal says that while it’s not for everyone, bloating, and gas are often signs of lactose intolerance, or the inability to fully digest the sugar (lactose) in cow’s milk products. (Lactose intolerance is the most common type of intolerance, he notes.)

If lactose intolerance is the cause of bloating, you may also experience stomach pain or diarrhea a few hours after eating or drinking dairy products such as milk, yogurt, cheese, and ice cream.

Stomach pain

According to Dr. Sonpal, abdominal pain, which is usually accompanied by (or is the result of) too much bloating and gas is another typical sign of intolerance.

Abdominal pain varies from person to person, but when it is caused by intolerance, it is usually felt as cramping in the middle and lower abdomen.


According to Dr. Sonpaul, when your body cannot digest or break down certain foods, diarrhea is a typical side effect. That’s why it’s a common sign that you may be sensitive to a recently eaten food.

“If you often have diarrhea after eating, you may have a digestive disorder when eating certain foods,” he says. “Most likely, lactose or gluten is to blame, but they are not the only ones.”


According to the Cleveland Clinic, although it may seem strange, headaches are another sign of food intolerance. And in severe cases, food intolerance can even cause migraines.

Immunoglobulin G (IgG) antibodies are the most common type of antibody in your blood. When you eat something that your body perceives as a threat, it releases these antibodies into the bloodstream, says Dr. Sonpal. Although it doesn’t happen to everyone, sometimes IgG antibodies can cause migraines and headaches.


Have you ever eaten something and immediately felt very lethargic or tired? The reason may be a drop in blood sugar, but sometimes feeling foggy can be a sign of food intolerance.

When you eat foods that your body can’t digest, your adrenal glands produce cortisol (a stress hormone) to help fight and reduce irritation and inflammation, says Dr. Sonpal. “This can cause fatigue if your adrenal glands are regularly producing cortisol to fight the body’s inflammatory response,” he adds.

4 common food intolerances


According to the Cleveland Clinic, lactose intolerance (a type of sugar found in dairy products) is the most common type of intolerance.

“If you are lactose intolerant, depending on your level of sensitivity, you may need to either eliminate or reduce your intake of lactose-containing foods,” says Bonnie Taub-Dix, MD, author of Read Before You Eat: You’re From Label to Table.

Although dairy products are rich in vitamins and minerals, you can still reap these benefits while avoiding lactose by choosing fortified milk substitutes such as almond milk.


Gluten is a protein found in wheat, rye, and barley, as well as derivatives of these grains. Although gluten intolerance is not quite the same as celiac disease (an immune reaction to gluten), your digestive system may still experience inflammation and anxiety when you eat these grains.


According to the Cleveland Clinic, as with gluten or lactose, some people may experience symptoms of food intolerance when they eat eggs, especially if the yolk is intact.


Although nut intolerance or sensitivity is usually not as serious as a nut allergy, it can still cause severe digestive discomfort.

What to do if you think you have a food intolerance

Suspect you have a food intolerance? Sonpal says that the next steps you take depend on the symptoms you are experiencing. If your symptoms are very painful or interfere with your ability to perform daily tasks, it’s best to see a doctor as soon as possible.

But if your symptoms are treatable, you can try to find the culprit on the y, he says. Here’s how to do it:

Make a list of the foods you ate before your symptoms started.

Then give up one of these foods for about two weeks and observe your symptoms. For example, if you ate yogurt with nutty muesli, dairy products or nuts could be the culprit. Instead of eliminating both of them from your diet, try avoiding dairy products for two weeks but continuing to eat nuts and see if your symptoms persist.

If you still experience symptoms while avoiding these foods, it was probably not the food that was the problem. After two weeks, re-add that food or food group to your diet and try eliminating the other food to see if that causes the problem. Continue this process until you find the culprit.

If you notice that your symptoms have decreased over a two-week period, gradually add that food back into your diet and pay attention to your body. If you feel that your symptoms are returning, you should give up this food and consult a nutritionist who can help you create a safe eating plan.

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Written by Emma Miller

I am a registered dietitian nutritionist and own a private nutrition practice, where I provide one-on-one nutritional counseling to patients. I specialize in chronic disease prevention/ management, vegan/ vegetarian nutrition, pre-natal/ postpartum nutrition, wellness coaching, medical nutrition therapy, and weight management.

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