An elimination diet is a gold standard for identifying food sensitivities. The basic premise is to remove an item from your diet for 3-4 weeks, reintroduce it, and observe the effects. If the reintroduction increases symptoms, the food should be kept out of your diet at least for the short term. It is important to reintroduce items one at a time (e.g., butter as butter not as a component in a wheat-flour-based cake) and in a quantity significant enough to cause a reaction (a few servings). Here is an example symptom tracker.
There are lab tests to determine food sensitivities (e.g., IgG antibody testing), but there are limitations of them based on the test itself, as well as how the food is prepared, processed, and/or how frequently it is consumed by the individual. In addition, there are potentially problematic food additives and colorings for which specific testing is not available. Therefore, an elimination diet completely removes many of these factors and becomes a thorough means to determine the foods best tolerated. There are a lot of variants of the elimination diet and here is the punchline: they all have utility. No one elimination diet is perfect for everyone.
Dairy and gluten (or wheat) are the most commonly eliminated items. Eliminating the “big-8” allergens would include dairy and wheat as well as eggs, fish, shellfish, tree nuts, peanuts, and soy. Paleo diets also exclude all grains, corn, potatoes, legumes, and peas. Other diets specify certain additives and types of added sugar to exclude, and some autoimmune protocols have limitations of specific vegetables such as nightshades and spices like cumin. Some people eliminate histamine or salicylate-containing foods like vinegar and green olives, respectively. There are FODMAP (Fermentable, Oligo-, Di-, Mono-saccharide and Polyol) diets where garlic, onions, and apples are off the table and some research indicates spinach may be problematic for people with multiple sclerosis.
There is a certain amount of fear-mongering that can occur in the blogosphere with warnings on any food. It is possible that any food may be problematic for some, but that does not mean that all of them need to be avoided by everyone forever.
While elimination diets are powerful tools, they are tools and not necessarily a representation of an optimal long-term diet. Particularly, eliminating plant materials – such as legumes, vegetables, fruits, and even grains – limits the diversity of the micronutrients, fibers, and phytochemicals in your diet. (To be clear: this is legumes, vegetables, fruits, and grains as the whole-food and kitchen prepped variety, not as components in processed foods.)
Micronutrients (vitamins and minerals) are vital to one’s health, but no one food (even kale!) provides the optimal concentrations of all of them. Diverse plant matter also provides different fibers for the gut microbiota and being too restrictive can negatively impact it (and by extension, your health). Plant material also contains more than 5,000 phytochemicals (think lycopene in tomatoes), many of which we do not yet know their health benefits. Why eliminate plant matter if you do not have to? Yes, eliminate the items not associated with health (e.g., high-fructose corn syrup) and any that are associated with symptoms for you, but keep and/or re-introduce the rest.
As an example, beans are often avoided. They do have lectins, but they also have fiber and polyphenols, were eaten by our ancestors, and are also associated with some pretty good glycemic control. [This is a good segway to discuss gas as a symptom. Gas is a natural byproduct of your gut microbiota eating fiber while also producing compounds like butyrate, which has systemic anti-inflammatory effects. Gas is not a foolproof symptom of an adverse reaction. Many people can eat beans without a problem and also receive the nutrient benefits (despite increased gas when compared to spinach).]
All the elimination diet variants are useful and can be used to determine individual responses to food. Certain foods for certain individuals should be avoided for life. People with celiac and gluten is a good example. Other foods will have to be avoided for a period of time only; people may have fructose malabsorption due to a separate gastrointestinal issue. Once an underlying dysfunction is addressed, the individual can often re-assimilate some of the once problematic foods increasing nutrient diversity (and enjoyment!) in their diet. Elimination diets are powerful tools, but the ultimate goal should be maximum diversity in the diet.