How to diagnose food intolerance

How to diagnose food intolerance

Do you feel that you have a problem with food causing digestive symptoms? Have you have ever been tempted to pay for a test that claims to identify your food intolerance? Here, we have put together all you need to know about ‘food intolerance testing.’

There are a few tests that are widely marketed in a way that would suggest that they can test you for a food intolerance (at a price). Unfortunately, there is no evidence that these tests can successfully identify a food intolerance.

IgG Blood Test

IgG is a protein in the blood that functions as an antibody. These commerical tests look for IgG4 for many food groups in the blood. If a result is positive, it is advised that you remove that food from the diet.

There is no strong evidence that these tests accurately identify a food intolerance. In fact, allergy doctors have investigated these tests and they have shown that you’re more likely to be told you have a positive food intolerance to a food you consumer regularly, not one you’re intolerant too.

Applied Kinesiology

This test reports to identify how the muscles in your body respond when a vial food is held. There is no scientific basis for this test.

Hair Analysis

This is where a small sample of hair is sent to a laboratory for testing. It can be used to identify heavy metal poisoning and drug use over time, but there is no good evidence that it is a way of identifying a food intolerance.


This test is where white cells in the blood are mixed with different food groups. If the cells swell up, then you are told you are intolerant to that food group. There is no scientific basis for this test.

Vega (electrodermal) Test

This test measures electronic current when the body is exposed to a food item. There is no scientific basis for this test either.

How to diagnose food intoleranceYou may hear people saying they feel a lot better once they removed a food that one of the above tests suggested they were intolerant to. Two of the common foods consumed in the UK are milk and wheat. In these intolerance tests, these two groups often prove positive. However, people with Irritable Bowel Syndrome (IBS) for example, can have intolerances to the lactose (a sugar in milk) and fructans (a carbohydrate in wheat). This explains why (for some people) symptoms may improve when removing these groups from their diet. But this doesn’t mean that completely excluding one or both of these food groups is fully necessary. For example, lactose free cow’s milk is suitable in IBS. Being overly restricted can risk malnutrition.

How to diagnose food intolerance

The gold standard method of identifying a food intolerance is to exclude the food item. Symptoms should go when removing the food, and more importantly, reintroduce the food and symptoms should return.* No testing is needed and therefore, advice should be sought from a dietitian throughout the process. Ask your doctor to see a dietitian if this applies to you.

Perhaps more importantly, do no self-diagnose your symptoms. See your doctor before you change your diet to get the true cause of symptoms identified.

*This should not be attempted in food allergy or where allergy is suspected, please seek specialist advice.

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How to diagnose food intolerance

If you live with chronic abdominal pain, diarrhea, or constipation, it can be debilitating. The fear of having adverse gastrointestinal conditions may keep you at home near your bathroom. You may live like this for years, not knowing the root cause of your condition. Also, you might possibly be too embarrassed to discuss your symptoms with your healthcare practitioner.

On the other hand, you may have already undergone so many tests and procedures without finding a solution that you continue to suffer, feeling as though there is truly no solution. What do you do when your doctor has ruled out relatively common diagnoses, such as irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD), yet you still have non-specific symptoms pointing to a gastrointestinal condition? Have you ever thought you could have a food intolerance?

A food intolerance is a response to a food your system has trouble digesting. For example, Sucrose Intolerance, medically known as Congenital Sucrase-Isomaltase Deficiency (CSID), lactose intolerance, and gluten intolerance are all food intolerances. There are several methods to help determine if a food intolerance exists.

Food Diary

A food diary is a tool used to track everything you eat on a day-to-day basis. A doctor may recommend a diary in an effort to determine when symptoms are occurring and if those symptoms are related to foods you consume. Tracking everything you eat, along with your mood and physical condition, is important.

Are you feeling anxious? Have you been sick with the flu? Do you have a headache? Are you in a hurry and eating on the run? Each of these situations can affect digestion and how you may feel after eating. Alternatively, one sneaky ingredient may be the culprit for the stomach discomfort. Gathering as much information as possible is important in tracking down your problem.

Several food diary templates, as well as apps, can be downloaded onto a smartphone. Choose one that is the most helpful and inspires your participation. Here is a list of the five, best food-tracking apps, found at Apps can provide very detailed information about food down to the brand. They also have reminders to help you stay on track.

FODMAP Elimination Diet

After reviewing a food diary, a doctor may request you try a FODMAP elimination diet. Not a diet used for weight loss, a FODMAP elimination diet is one in which certain foods suspected of triggering a negative gastrointestinal response are removed from the diet. FODMAP is an acronym outlining specific carbohydrates that are known to cause non-specific gastrointestinal symptoms like gas, bloating constipation, and diarrhea. You must first eliminate these foods from your diet for two-to-eight weeks and then reintroduce them one by one to see which foods are tolerated and which foods cause symptoms.

Blood Test

Blood tests are most often used to rule out a food allergy. A food allergy is an immune response by the body to something consumed or even just touched. The onset of symptoms occurs immediately since the body is releasing antibodies to fight the unwanted food in the system. In regard to food intolerances, blood tests are most often used to diagnose either celiac disease, an autoimmune disease, and lactose intolerance, the inability to digest the milk sugar lactose.

Sucrose Hydrogen Breath Test

A sucrose hydrogen breath test can be used to aid in diagnosing individuals suffering from Sucrose Intolerance, medically known as Congenital Sucrase-Isomaltase Deficiency (CSID). CSID is a condition in which you are unable to digest common white table sugar and starch. In other words, with Sucrose Intolerance, your body lacks an important enzyme that allows your digestive system to break down sucrose.

You begin the breath test by drinking a solution containing sucrose. Then you breathe into a bag every 15 to 20 minutes as you digest the solution. After each breathing session, a doctor uses a syringe to empty the bag. The air is measured to see if any hydrogen is present. In a normal evaluation, very little hydrogen is present. However, if you have a Sucrose Intolerance, undigested sucrose in the colon will ferment and cause hydrogen gas to develop, indicating that Sucrose Intolerance might exist. While sucrose hydrogen breath tests are fairly simple to do, they can take two to three hours and can give you GI symptoms if you have a sucrose intolerance.


An endoscopy is a procedure used to take a look at your digestive tract. This is procedure used to help diagnose CSID and celiac disease. In an endoscopy, a scope is inserted through the mouth, down the esophagus, and into the stomach and small intestine, giving the physician a clear view of the digestive system and the option of taking a sample of the tissue. The samples are then studied to look for the symptoms of CSID or evidence of damage and inflammation from celiac disease.

Under the supervision of a doctor, each of these tests is helpful in diagnosing a food intolerance.

How to diagnose food intolerance

You like the foods you eat. Sometimes, though, your foods don’t like you. It’s really your gastrointestinal (GI) tract that is responding with symptoms of food intolerance that can make you regret some of your food choices. Food intolerances are common. In fact, nearly everyone has eaten something that disagrees with them.

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If you’re sensitive to a food, you don’t necessarily have to remove it completely from your diet. The key is to identify the offending food and figure out how much, if any, of it you can eat without suffering the consequences.

“The most important thing is when you think you have a food sensitivity, really talk with your physician about it,” says Kristin Kirkpatrick, MS, RD, LD. “I see way too many people who cut foods out of their diet when maybe the food has nothing to do with it. You might be sensitive to one thing and not another. You have to do your due diligence.”

Why you’re intolerant

A food intolerance occurs when something in a food irritates your GI tract or you can’t digest that food due to a lack of necessary enzymes, sensitivity to certain components, or other factors.

Some signs of food intolerance are similar to those of a food allergy — namely, stomach pain, diarrhea, nausea and vomiting — but the two conditions differ in important ways. A food intolerance occurs in the GI tract, develops more gradually, and generally isn’t life threatening. Other symptoms of food intolerance include headaches and heartburn, and some evidence has linked food intolerances with joint pain and mood changes, including irritability and nervousness. Oftentimes, food-intolerance symptoms occur only if you eat a lot of a troublesome food or consume it frequently.

A true food allergy, however, is a larger immune system response that occurs suddenly when you are exposed to a food component that your body interprets as harmful. Food allergies can cause more severe, potentially life-threatening problems, such as chest pain, a sudden drop in blood pressure, and difficulties swallowing or breathing (call 911 immediately). And the symptoms of a food allergy can be triggered by exposure to even trace amounts of a problem food or food component.

Intolerance to lactose (the sugar found in milk and other dairy products) is the most common food intolerance, affecting about 1 in 10 Americans. Another common one is gluten, a protein in wheat, rye and barley that causes celiac disease as well as the less severe nonceliac gluten sensitivity.

It’s important to identify whether you have a food intolerance and not just diagnose yourself. If you have things that can’t be explained, especially GI issues, that’s when it’s time to think about getting evaluated.

Finding food intolerance

Your physician can order a blood test to find what’s causing your symptoms. More often, your doctor will recommend an elimination diet, in which you stop eating one or more potential problem foods for several weeks and gradually reintroduce them one at a time. As part of this process you should keep a food journal to document what you eat and how it affects you.

“You have to be very specific,” Kirkpatrick emphasizes. “If you do have a food sensitivity, it’s about looking at which foods you have to limit, but it doesn’t necessarily mean you have to give them up completely.”

Your doctor or dietitian may recommend certain digestive aids or alternatives that help you avoid GI symptoms — such as lactose-free dairy products, milk alternatives (like soy milk) or lactase supplements that can help you tolerate dairy.

“It can take a while to figure things out. You might be surprised about what foods you’re sensitive to,” Kirkpatrick says. “You have to take into consideration that it’s a process and it’s going to take some time. For a lot of people with food sensitivities, that’s the way to go.”

Common culprits for food intolerance

Here’s a look at common foods and food components that cause food intolerance and food allergies:

● Gluten (found in wheat, rye, and barley).

● Casein (a protein in milk products).

● Eggs (especially egg yolks).

Fish and shellfish.

● Peanuts or tree nuts (like pecans, almonds, walnuts).

● Sulfites (compounds in red wine and beer that are also added to certain foods).

● Some food additives, such as monosodium glutamate (MSG).

What you can do

  • Tell your doctor about GI symptoms you believe could result from a food intolerance, and ask about testing for a food sensitivity or allergy.
  • Follow your doctor’s advice about an elimination diet, and learn which foods you can eat and how much you can consume.
  • Keep a food journal and carefully document which foods you eat and how you react to them.
  • Carefully read food labels. Check the ingredients for problem foods or ingredients.
  • Ask your physician about your risks from food allergies and whether you should carry an emergency epinephrine injection.

This article originally appeared in Cleveland Clinic Men’s Health Advisor.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy