Allergy symptoms are frustrating, especially when you don’t know what’s causing them. From chronic gastrointestinal issues to hives and other rashes, to joint pain and shortness of breath, there are many uncomfortable and disconcerting reactions that can be attributed to food allergens.
But what exactly causes these reactions? Enter the elimination diet. As a certified allergy specialist, I often use elimination diets to help diagnose a food allergy, or to pinpoint a food intolerance or sensitivity.
What is an elimination diet?
An elimination diet is true to its name: it involves removing a specific food or group of foods from your diet for a set period of time, and then gradually reintroducing the food(s) to determine what causes the adverse reaction. The process behind elimination and reintroduction requires careful precision, and it should always be done under the guidance and supervision of a certified allergist, dietitian or other specialized healthcare provider.
The guiding practitioner will watch for severe reactions, help you avoid nutrient deficiencies during the elimination phase, and offer advice for reading food labels, avoiding specific foods and keeping a meticulous food journal.
A food elimination diet — which often takes place over a number of weeks — isn’t usually used on its own to diagnose. Rather, it’s a tool used in conjunction with immunoglobulin E (IgE) allergy blood tests or skin prick allergy tests and a detailed health history to arrive at a diagnosis. Elimination diets can also help identify food intolerances and sensitivities.
The concept of an elimination diet goes back to 1944, when Dr. Albert H. Rowe published “Elimination Diets and the Patient's Allergies.”¹ Despite being close to 80 years old, this handbook contains concepts still in practice today.
How does an elimination diet work?
Protocols may differ by practitioner and by patient. In my practice, I usually have patients eliminate individual foods for a period of eight days, while other healthcare providers may advise elimination for a number of weeks. During the elimination phase, we observe whether removing the food resolves the symptoms that brought the patient to me in the first place.
Single food versus multiple food elimination
Most often, foods are removed from your diet one at a time. But occasionally, in people who are experiencing systemic allergy symptoms like total body hives that require steroid treatment, many foods are eliminated at once. This more drastic approach provides a blank slate which can help get symptoms under control more quickly and make figuring out the problem food(s) easier.
Reintroduction phase and oral food challenges
After the elimination period, the foods that have been removed are reintroduced through oral food challenges.² The reintroduction process involves eating the eliminated items to see how your body reacts. I often greenlight an at-home challenge for patients who are experiencing less severe food allergy symptoms, like digestive discomfort, mild hives or rashes, but for people who have experienced anaphylaxis — a severe allergic reaction that sends the body into shock and requires immediate medical treatment — the challenge is completed under my supervision. Patients who have experienced severe symptoms shouldn't reintroduce foods on their own.
An elimination diet as a form of treatment
An elimination diet may also be used as a form of treatment. For instance, if an IgE blood test or skin prick test confirms that you're allergic to wheat, then a diet that eliminates wheat may be part of your treatment plan. Similarly, people with certain conditions, such as the immune condition eosinophilic esophagitis (EOE) or irritable bowel syndrome (IBS), might be prescribed an elimination diet that removes some of the most common trigger foods. These items may or may not be reintroduced as part of a challenge in the future.
Why should you do an elimination diet?
Many people wonder what a medically supervised elimination diet offers if food allergy testing is available, but most allergy specialists feel that allergy and sensitivity testing is both a science and an art.
It’s true that IgE blood work and skin prick testing are reliable primary methods of food allergy testing.³ These tests measure the presence of IgE antibodies, which indicate an immune system reaction to a given substance. But they’re not perfect. Sometimes these tests will show a positive result for a food allergen that a patient has never reacted to, possibly due to a cross-reaction or because they’ve built up a tolerance. For example, shrimp and dust mites may have a protein in common, so if someone is allergic to dust mites, they might also test positive for shrimp even though they’ve never had a reaction to it. Certain nuts are also known for cross-reactions, including cashews and pistachios, and walnuts and pecans.
On the opposite side of the spectrum, food allergy testing may come back negative even if someone regularly reacts to the food. That doesn’t mean the person’s symptoms aren’t valid — they may have a food intolerance or hypersensitivity that can’t be detected through blood work or skin prick testing. They could also be allergic to something other than food.
In my opinion, an elimination diet is the only way to truly confirm that a certain food is an issue, because it trials the theories of IgE testing in real time. The exception, of course, is when a patient has an intense allergic reaction any time the food is eaten (like an anaphylactic reaction to nuts); then, an elimination diet isn’t necessary because the allergy is clear.
Why is combining food allergy diagnosis strategies important?
A detailed medical history, lab testing, a guided elimination diet and oral food challenges are required to get a complete picture of a patient’s allergies.
An elimination diet and oral food challenges can help confirm the lab results while also filling in any gaps left by the IgE results. Though it’s possible to identify problematic foods through elimination and reintroduction alone, I use the combination method because testing also helps to determine which foods should be eliminated and challenged next.
What is the process for an elimination diet?
For me, the first step is getting the patient involved in the process. Eliminating foods and then challenging them isn’t easy, so committing to the process is key.
1. Keep a thorough and detailed food diary for two weeks.
When I say detailed, I mean really detailed. You wouldn’t just write “salad” for lunch. Instead, you'd write, “baby spinach, cherry tomatoes, red pepper, feta cheese, chicken breast, olive oil and vinegar.” You need to start reading labels and including anything that might be noteworthy. Did the crackers you just ate contain eggs, dairy and soy, on top of wheat? Was garlic or onion in the flavorings of foods that made you ill? I tell my patients that they have to help me help them by playing detective in their own pantries and refrigerators.
I also ask my patients to record how they're feeling a few hours after eating, noting any symptoms like bloating, digestive discomfort, rashes or hives in the diary. These can be important clues when we're deciding on which foods to eliminate and challenge later on.
The food diary is particularly useful because people don’t always notice exactly what they’re eating. For example, they may tell me they don't eat a lot of dairy products, so dairy probably isn't causing their symptoms. But then, through their food diary, we discover they're having yogurt with breakfast, cheese at lunch and ice cream for dessert. Milk is also found in foods you might not expect, like baked goods, crackers and candy.
2. Analyze the food diary to look for patterns.
Once the food diary is complete, I ask two main questions:
- Which foods are you eating most often?
- Which of these common food allergens frequently appear in your diet?:
- Tree nuts (e.g. walnuts, almonds, cashews)
- Shellfish (e.g. crab, shrimp, lobster)
I then compare the diary to the food allergy test results (IgE testing can be completed at the same time as the food diary) to come up with a list of foods to eliminate and challenge. We start with the foods that are most likely a problem and work our way down to the foods that are least likely.
3. Systematically eliminate potential problem foods.
Starting at the top of the list, I advise patients to take one food out of their diet for eight days. I usually have my patients do this from Saturday to Saturday since people typically find it easier to start on a day when they're not working.
In some cases, there are acceptable substitutions, or foods that mimic a texture or taste, that patients find helpful. Here are some I recommend:
- Dairy milk alternatives: Coconut milk, almond milk, oat milk, flax milk, rice milk, hemp milk or other mammalian milk if tolerated (goat, sheep, even camel milk).
- Dairy cheese alternatives: Avocado, dairy-free cheese substitutes, feta (made from sheep's milk, if tolerated).
- Wheat bread alternatives: Gluten-free bread made from rice, sorghum, amaranth, quinoa and corn, corn tortillas.
- Egg alternatives: Flax egg (one tablespoon flaxseed combined with three tablespoons water), tofu (if not eliminating soy).
- Peanut alternatives: Tree nuts including almonds, cashews, walnuts, pecans and peanut butter alternatives like soy-based butter, legume-based butter, seed butter.
- Tree nut alternatives: Peanuts, soy-based butter, legume-based butter, seed butter.
- Fish alternatives: Poultry, red meats, vegan fish-sauce substitutes (for cooking).
- Shellfish alternatives: Crab alternatives (made with whitefish and wheat).
- Soy sauce alternatives: Coconut aminos.
- Soybeans: Chickpeas.
Identifying the culprit(s)
If you feel better and your symptoms start to resolve during the eight days you’ve eliminated a specific food, that's a solid clue that what you've eliminated is causing your problem. But, some people don't notice a difference when they eliminate the food; they only notice a real change in their symptoms when reintroducing the suspicious food during the challenge step.
4. Reintroduce potential problem foods one at a time.
After the elimination period, I instruct my patients to reintroduce an eliminated food in a process known as a challenge. They do this challenge over a weekend in case the symptoms from reintroduction are unpleasant and interfere with work.
To reintroduce, a patient will eat the eliminated food twice in one day, usually in close succession. So if you’re testing milk, I'd have you drink a glass of milk in the morning and then wait an hour. If you experience symptoms, we stop there. We now know that milk is one of your problem foods. From there, we may still eliminate and challenge a few other foods, depending on the specific situation.
If you have no symptoms after that first glass of milk, then I’d instruct you to drink another glass of milk. If you still feel good after several hours, we can say, pretty conclusively, that milk isn't a problem food and move to the next food on the list.
Once we've identified the problem food(s), those items are removed from the person's diet for a period of time. Depending on whether the problem food is a true allergen or an intolerance, it may be possible to reintroduce it again after a few months or years in another food challenge.
For some people, oral immunotherapy (OIT)⁴ may also be an option. OIT is a newer form of allergen management, typically only used for severe peanut allergies (for now, at least). OIT gradually reintroduces true food allergens in very small amounts until they can be tolerated in increasing doses. Because some severe food allergies can cause anaphylaxis, OIT must be done under the supervision of a certified allergist.
Elimination diets can be challenging. They require a degree of discipline and fastidiousness that not everyone understands before starting the process. For most people, this means they need to prepare their own foods during the process, as most restaurants can't guarantee that food won’t be contaminated with potential allergens.
But in the end, the process is worth the effort. Combined with lab testing, an elimination diet is the gold standard in diagnosing food allergies and food intolerances.