How to Diagnose Food Intolerance

Co-authored by Marsha Durkin, RN

Updated: March 29, 2019

Explore this Article Comparing Food Allergy and Intolerance Symptoms Keeping a Food Diary Ruling Out Allergies and Eliminating Foods Ask a Question Related Articles References

Having a food intolerance can be hard to diagnose, especially if you're not sure if it's an intolerance or allergy. Pay close attention to your symptoms that might indicate that you have an allergy or intolerance, and then see your doctor. Keep a food diary and talk to your doctor about an elimination diet to pinpoint your diagnosis.

Part 1
Comparing Food Allergy and Intolerance Symptoms

  1. 1
    Pay attention to the timing of your symptoms. If you have a food intolerance, you won't see a reaction to the food you eat right away. A food allergy will result in a more immediate reaction.[1]
    • Digestive symptoms caused by a food intolerance usually come on gradually over the course of a couple of hours.
    • A food allergy usually results in symptoms almost immediately.
  2. 2
    Be on the lookout for stomach pain for food intolerance. If your stomach pain is related to a food intolerance, it will come a few hours after you eat the food. The pain can be mild or severe, depending on how much of the food you ate and how severe your intolerance is.[2]
    • This stomach pain may also include heartburn. Heartburn is a burning sensation near the top of your stomach or in your throat.
  3. 3
    Look for bloating, excess gas, or diarrhea. If you develop bloating, gas, or diarrhea a few hours after eating, chances are you're intolerant of one of the foods you ate. If you develop these symptoms more than 2 or 3 hours after you ate, they are likely caused by something else.[3]
  4. 4
    Keep an eye on how much food you can eat. If you have a food intolerance, you might be able to eat small amounts of the offending foods without symptoms. If you have a food allergy, you won't be able to eat any of the food you're allergic to without having a reaction.[4]
  5. 5
    Look for rashes or itchy skin for evidence of food allergies. Rashes or itchy skin usually indicate a food allergy, rather than an intolerance. You will rarely experience these symptoms as a result of an intolerance.[5]
    • If you notice that certain foods seem to cause rashes, swelling in your mouth or throat, or hives, see your doctor immediately. These are symptoms of an allergic reaction, can be severe, and might need immediate treatment.

Part 2
Keeping a Food Diary

  1. 1
    Divide your diary into individual days. It's important to track what you're eating every single day. You might not eat the foods you're intolerant of every single day and you might be intolerant of more than 1 food. Keeping your diary every day can help you detect a pattern.[6]
  2. 2
    Track every single food you eat. As you keep your diary, make sure you write down all the food you eat. This includes regular meals, snacks, desserts, and anything you drink. Even if you eat just a small amount of food, you should still track it.[7]
    • You can use food diary apps if you have a smartphone. It's an easy way to track everything without having to carry a notebook and pencil with you. There are also websites you can use to track your food.
  3. 3
    Write down any symptoms that develop. After you've written down each meal or snack, write down any symptoms that you develop after eating. It's important that you write them down as soon as they develop. It makes it easier to see which foods might be causing the symptoms.[8]
  4. 4
    Make sure you note times for your meals and symptoms. Make sure you write down what time you ate each food, and what time you developed symptoms. It makes it easier for you and your doctor to see which foods might be causing your symptoms.[9]

Part 3
Ruling Out Allergies and Eliminating Foods

  1. 1
    Review your food diary for likely causes. Once you've been keeping your food diary for a couple of weeks, look it over. If you see a pattern where you eat certain foods and then develop symptoms a few hours later, write those foods down. Those are likely the foods that your body is intolerant of, and they're a good place to start when diagnosing your food intolerance.[10]
  2. 2
    Talk to a dietitian or your doctor. Before you begin an elimination diet, you should speak to a dietitian or your doctor. Make sure you bring your food diary with you and your list of suspect foods. Your doctor or dietitian can help you narrow down which food and drinks to avoid, how to read food labels, how long your diet should last, and if you need to supplement your diet with alternative forms of nutrition.[11]
  3. 3
    Undergo allergy testing. If it's not clear to your doctor where you have an allergy or intolerance (some food allergies can be mild enough to be mistaken for intolerance), they may recommend an allergy test. There are 2 types of tests. Your doctor will choose the best one for your condition.[12]
    • If your allergies seem severe or developed quickly, your doctor will order a skin-prick or blood test.
    • If your allergies are mild or your doctor is unsure whether you have an allergy, your doctor may suggest an elimination diet instead.
  4. 4
    Cut suspected foods from your diet for 2 to 6 weeks to test for intolerance or mild allergies. Removing all of the foods you suspect of making you sick lets you reintroduce them slowly later. Cut all of the foods on your list from your diet and keep them out of your diet for 2 to 6 weeks. If your symptoms improve, one of those foods is likely what's causing your symptoms.[13]
    • Your doctor will tell you exactly how long your diet should last.
    • Make sure you're noting in your food diary which foods you're cutting and when and if you develop symptoms again.
    • If your symptoms don't disappear, see your doctor. Your symptoms might be caused by something else, or you may have missed a pattern in your food diary. Your doctor can help you figure out the next steps.
  5. 5
    Reintroduce the foods you cut. Once your symptoms have subsided, you can start reintroducing the foods you cut from your diet. Reintroduce them one at a time for a week or so. If your symptoms don't reappear, reintroduce another food. If your symptoms do return, the food you reintroduced more recently is likely the food causing your symptoms.[14]
    • Your doctor should tell you which foods to reintroduce when.
    • Keep tracking your intake in your food diary. It will help you see exactly which foods cause the symptoms to reappear.
  6. 6
    See your doctor again. Once you've completed your diet, your doctor will likely want to see you again. Make a follow-up appointment once you've completed your elimination diet, taking your food diary with you. Your doctor should be able to then diagnose which foods are causing your symptoms.

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    Article Info

    This article was co-authored by Marsha Durkin, RN. Marsha Durkin is a Registered Nurse in Wisconsin. She received her Associates Degree in Nursing from Olney Central College in 1987.

    Categories: Food Allergies

    Thanks to all authors for creating a page that has been read 929 times.
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