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Lectins are proteins in plants that have been associated with both positive and negative health effects.

Some plant-based foods, such as beans and legumes, whole grains, and certain vegetables contain a high amount of lectins.

Read on to learn more about lectins and the lectin-free diet. What does science have to say about this diet? Why do some people recommend it, and does the evidence support their claims?

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Undercooked red kidney beans may cause severe nausea, diarrhea, and vomiting due to a lectin called phytohaemagglutinin.

Lectins are a type of protein that, in humans, may help cells interact with one another. Some scientists also believe that lectins provide a form of defense in plants to keep insects away.

These proteins also contain nitrogen, which is needed for plants to grow. While many parts of plants contain lectins, the seed is the part that people eat most often.

Lectins may impact health in multiple ways, ranging from digestion to chronic disease risk. They have been shown to cause red blood cells to cluster together.

They are categorized as antinutrients since they block the absorption of some nutrients.

Lectins may cause an upset stomach when plant foods are eaten uncooked. They are also the reason why it can be dangerous to eat undercooked legumes.

The lectin in red kidney beans is called phytohaemagglutinin. It is responsible for red kidney bean poisoning, which results from eating raw or undercooked kidney beans. According to the United States Food and Drug Administration (FDA), consuming just four raw kidney beans could cause symptoms including severe nausea, vomiting, and diarrhea.

Cooking methods that use moist heat are helpful for decreasing the number of lectins in plants. Cooking also breaks down some plant starch into simpler carbohydrates. Lectins like to attach to carbohydrates and are removed from the body before they cause negative effects.

Slow cookers are not recommended for preparing kidney beans because the temperature is not high enough to eliminate lectins. Ways to decrease lectins in foods include:

  • boiling
  • fermentation
  • sprouting
  • peeling
  • deseeding
  • pressure cooking

While lectins have some undesirable effects, they also have some positive ones. Small amounts of lectins may help the good bacteria that live in human digestive systems.

Research suggests that lectins may be useful for helping to identify and diagnose cancer. Lectins are also being studied for their potential to slow down the rate that cancer cells multiply.

Researchers are even looking at lectins as potential treatments for illnesses caused by bacteria, fungi, and viruses.

Dr. Steven Gundry popularized the lectin-free diet. He is a former heart surgeon who switched his focus to food and supplement-based medicine.

Dr. Gundry describes lectins as the main danger found in the American diet. In response, he has written a book that provides information on how to avoid lectins, alternative food choices, and recipes.

According to the book, Dr. Gundry's plan helps people improve their health and reduce their body weight. The plan also includes supplements Dr. Gundry developed that are sold under the GundryMD brand.

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Alongside many other foods, Dr Gundry recommends eating sweet potatoes to limit the intake of lectins.

Some scientists believe lectins are harmful and cause inflammation. An older article links them to autoimmune diseases, including celiac disease, diabetes, and rheumatoid arthritis.

One article discusses the research associated with wheat germ lectin. It may impact the immune system by increasing inflammation.

Long-term inflammation is linked to many serious medical conditions, including heart disease, cancer, and depression.

Following a lectin-free diet could be a way to lower inflammation in the body. However, more research in humans is needed before the effect can be confirmed.

The authors also report that lectins may make it easier for bacteria or other toxins to cross the gut barrier. However, they also state that whole grains contain antioxidants, which help fight inflammation. This factor could make up for lectin's potentially harmful effects.

The lectin-free diet is a restrictive plan, which may make it difficult for some people to follow it long-term. The plan also limits or cuts out many nutritious foods, such as whole grains, beans, and certain vegetables.

Research has shown that consuming whole grains can help reduce the risk for heart disease, diabetes, and cancer.

Fruits and vegetables also have many associated health benefits. Eating more fruits and vegetables may lower the risk for multiple conditions, including heart and lung diseases. They may also impact cancer risk and help people avoid gaining weight.

A lectin-free diet may be difficult for vegetarians or vegans to follow, since legumes, nuts, seeds, and whole grains provide plant-based protein.

Legumes, whole grains, and fruit and vegetable peels also provide dietary fiber. A lectin-free diet could result in constipation if dietary fiber intake decreases.

Also, following a lectin-free diet may be expensive, as the plan recommends specialty milks, pasture-raised meats, and expensive supplements.

According to Dr. Gundry, the following foods are recommended for people trying to limit their lectin intake:

  • pasture-raised meats
  • A2 milk
  • cooked sweet potatoes
  • leafy, green vegetables
  • cruciferous vegetables, such as broccoli and Brussels sprouts
  • asparagus
  • garlic and onion
  • celery
  • mushrooms
  • avocado
  • olives or extra virgin olive oil, available to purchase online.

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To avoid lectins, peppers, tomatoes, and eggplants should be avoided.

According to Dr. Gundry, people should limit the following foods when trying to avoid lectins:

  • legumes, such as beans, peas, lentils, and peanuts
  • squash
  • nightshade vegetables, such as eggplant, peppers, potatoes, and tomatoes
  • fruit, although in-season fruit is allowed in moderation
  • grains

If grains are consumed, the plan recommends products made from white flour instead of wheat.

Dr. Gundry recommends completely avoiding the following foods:

  • corn
  • meat from corn-fed animals
  • A1 milk

While lectins may cause some damage, there is strong research to support the benefits of eating plant foods.

Many plants are high in lectins, but lectin levels can differ significantly between plant types. There are also many kinds of lectins, and some seem to be beneficial.

It is also important to be aware that much of the research on lectins has been via animal or test- tube studies. Furthermore, many studies have looked at single lectins instead of the foods that contain them.

More research is needed before following a lectin-free diet can be recommended. At this time, it seems to be more of a trend than a plan backed by science.