DEAR MAYO CLINIC: A friend of mine continues to speak highly about the health benefits of a diet where people eliminate lectins. She says it helped her lose weight and reduced her arthritis pain. What are lectins, and can a lectin-free diet cure autoimmune diseases and prevent other health problems?

ANSWER: Lectins are naturally occurring proteins that are found in all foods, but they are most concentrated in certain plants. Lectins serve a protective function for plants as they grow. They do not have nutritional value when consumed in foods.

Foods that contain high amounts of lectins include legumes, such as beans, lentils, peas and peanuts, as well as tomatoes, potatoes, eggplant, certain fruits, wheat and other grains.

While your diet can influence the way you feel, especially if you have a chronic condition, it is important to be aware of how elimination diets can negatively affect the body. This is particularly important if you are already on a restrictive diet.

Grains and legumes are a powerhouse of nutrients. They are rich in B vitamins, iron and fiber. These nutrients can be difficult to get if you are, say, gluten-free.

Despite many claims, no scientific evidence shows that eliminating dietary lectins will cure any medical disorders or conditions, including autoimmune diseases. Your friend may credit her weight loss success and better health to her diet, but I would question if she also eliminated other things that may have been contributing, such as limiting sugar, processed foods and excess salt.

Some research seems to indicate taking in large quantities of raw lectins could negatively affect health. But the amount you'd need to consume daily to get to that level is much higher than a typical diet would include. And other studies have shown that lectins break down when processed or cooked, so the risk of adverse health effects arising from lectin-rich foods that are not raw is not cause for concern.

In addition, most foods that contain lectins are recommended as part of a healthy, well-balanced diet. A large body of scientific evidence clearly supports the benefits of a diet rich in fruits, vegetables, whole grains, and nuts and seeds.

The health benefits you receive from including those foods in your diet outweigh any perceived benefits from avoiding foods with lectins. With that in mind, a diet that avoids lectins is not one most dietitians would typically recommend.

If you have a medical concern triggering symptoms that seem to be related to the foods you eat, speak to your primary care provider about having a consultation with a dietitian. Likewise, if you are simply eating a diet that includes a variety of foods and you're having symptoms that make you feel unwell, it often can be difficult to pinpoint the specific source of the problem on your own. It could be a food allergy or a food intolerance, or it may not be related to your diet at all.

Thus, it is important to speak to your health care professional to review and sort out the cause of your symptoms. Some medical centers have dietitians who specialize in gastrointestinal issues, and those professionals can help in these cases. Take time to speak with a health care professional who can review your diet and offer suggestions for modifying it in a way that may ease your symptoms.

A dietitian may recommend, for example, a short-term elimination diet, excluding certain categories of foods that tend to cause allergic reactions most often. Once those foods have been taken out of a diet, then they can carefully be reintroduced to identify possible causes of food-related symptoms. Based on that or other evaluations, a dietitian can make recommendations that fit the situation.

Rather than using a generalized approach and trying to apply it to everyone — such as avoiding all food with lectins — a diet that's structured and overseen by a dietitian and based on scientific evidence can be customized to accommodate a person's sensitivities. That type of systematic approach typically yields better long-term results than just avoiding a certain kind of food or a food ingredient and hoping to feel better. — Katherine Zeratsky, R.D.N., Endocrinology/Nutrition, Mayo Clinic, Rochester, Minnesota

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