Very few foods are perfect.
Most of them have both "good" and "bad" aspects.
Lectins are among the "bad" things that are frequently mentioned.
Lectins are a family of proteins found in pretty much all foods, especially legumes and grains.
Frequent consumption of large amounts of lectins has been shown to damage the lining of the digestive system ().
Some people claim that this causes increased gut permeability and drives autoimmune disease.
It is true that lectins can cause harm, but there is more to the story than we've been told. For example, it is easy to get rid of them with the right preparation methods.
Lectins are a diverse family of carbohydrate-binding proteins found in nature. All plants and animals contain them ().
These proteins play various roles in normal physiological functions, including those of our own bodies.
For example, they help cells and molecules stick to each other, and perform various functions related to the immune system.
Although all foods contain some lectins, only about 30% of the foods we eat contain them in significant amounts ().
Their function in plants is not clear, but they may have evolved as a survival mechanism.
Most plants do not want to be eaten, so having these damaging molecules may discourage animals from eating them in large amounts.
Just like other animals, humans are vulnerable to the toxicity of lectins. Concentrated amounts can cause digestive issues and long-term health problems.
In the case of the poison ricin (a lectin from the castor oil plant), they can even cause death.
Bottom Line: Lectins are a family of carbohydrate-binding proteins. They are found in all foods, but the highest amounts are found in legumes and grains.
Humans have problems digesting most lectins.
In fact, they are highly resistant to the body's digestive enzymes, and can easily pass through the stomach unchanged ().
The "stickiness" of lectins makes them prone to attaching to the intestinal wall.
There, they disrupt the body's routine maintenance of cells, so the everyday wear-and-tear that occurs in the intestine gradually worsens (, , , ).
This is the main reason why excessive lectin intake causes digestive distress.
The most extensively studied lectins are called phytohemagglutinins, which are mostly found in plants, especially legumes.
Uncooked (raw) legumes like kidney beans are the biggest sources of these lectins.
Eating raw kidney beans can lead to lectin poisoning, the main symptoms of which include severe abdominal pain, vomiting and diarrhea ().
However, keep in mind that humans don't typically eat raw legumes. They are always cooked before consumption.
Bottom Line: Lectins can cause digestive distress in humans. Some lectins, such as the phytohaemagglutinins in raw legumes, can be downright poisonous.
Repeated exposure to lectins may eventually damage the gut wall.
Unwanted substances can then more easily penetrate the gut, and may enter the bloodstream.
This condition of increased gut permeability is often called "leaky gut" ().
When lectins "leak" into the bloodstream, they can interact with glycoproteins on cell surfaces ().
Lectins can also interact with antibodies, which are a core component of the immune system. This may cause an immune reaction not only against the lectins, but also the body tissues to which the lectins are bound ().
This type of response is known as an autoimmune reaction, where the immune system mistakenly starts attacking the body's own structures. This is how lectins may increase the risk of autoimmune diseases.
Bottom Line: Repeated exposure to large amounts of lectins may increase gut permeability. Some researchers believe that dietary lectins can raise the risk of autoimmune disease.
Proponents of the paleo diet claim that lectins are harmful.
Due to the lectins (and other anti-nutrients), they say that people should remove legumes and grains from their diet.
However, what is often left out of the discussion, is that lectins can be virtually eliminated with cooking.
In fact, boiling legumes in water eliminates almost all lectin activity (, ).
While raw red kidney beans contain 20,000 to 70,000 hau (hemagglutinating unit), cooked kidney beans contain only 200-400 hau, a massive drop.
In one study, lectins in soybeans were mostly eliminated when the beans were boiled for only 5 to 10 minutes ().
It makes no sense to avoid legumes because of lectin activity in raw legumes. People don't eat raw legumes, they are always cooked first.
Bottom Line: Cooking at high temperatures effectively eliminates lectin activity from foods like legumes, making them perfectly safe to eat.
Cooking is not the only way to degrade lectins in foods.
Soaking or sprouting seeds and grains helps to eliminate lectins and other anti-nutrients (, ).
Fermenting the foods can also work, by allowing friendly bacteria to digest the anti-nutrients (, , ).
This is why traditionally prepared whole grains are much healthier. Populations that traditionally ate grains usually treated them first with some form of fermentation.
Grains today may be more problematic because they are no longer prepared like they used to be, and are therefore higher in anti-nutrients.
Bottom Line: Soaking, sprouting and fermenting foods can eliminate lectins and other anti-nutrients, especially from grains.
It is true that dietary lectins are toxic in large doses, but humans don't eat large doses.
The lectin-rich foods we consume, like grains and legumes, are almost always cooked in some way beforehand.
This leaves only a negligible amount of lectins, making these foods safe to eat for the majority of people.
However, the amounts in foods are probably way too low for this to be a real concern for otherwise healthy individuals.
Most of these lectin-containing foods are high in vitamins, minerals, fiber, antioxidants and all sorts of beneficial compounds.
The benefits of these healthy nutrients far outweigh the negative effects of trace amounts of lectins.