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Nutrition > Food Facts


Dr. med. André Sommer

Dr. med. André Sommer

Lectins are carbohydrate-binding proteins (glycoproteins) that can agglutinate cells without changing them. Because of this property, they are also called agglutinins. They are also anti-nutrients that affect our nutrient utilization. This happens due to damage to the microvilli (cell processes that help improve the exchange of substances) in the intestinal mucosa. The consequences are a reduction in the size of the intestinal surface and reduced nutrient absorption. Lectins are found in most plants and therefore also in human food. They take on a natural protective function against diseases, pests, herbivorous insects and animals. They occur in a particularly high concentration in the seeds of the respective plants. In lower concentrations, however, they can also be found in other plant tissues, such as tubers, onions, rhizomes and bark. They have both harmful and useful properties for humans.

How does the consumption of lectins affect the intestine?

Lectins cannot be digested (completely). They resist the low (acidic) pH in the stomach and thus get into the intestine, where they can withstand the digestive enzymes. They bind to the cells of the intestinal mucosa and thus exert a negative influence on the exchange, the multiplication and the loss of these cells. The microvilli on the villi are damaged.** **These are part of the intestinal mucosa and, when in a healthy state, enlarge the surface of the intestine and thus ensure optimal nutrient absorption. If they are damaged, the digestion and absorption of nutrients is impaired. Lctins are therefore described as anti-nutrients. Changes in the cell metabolism of the intestinal wall (epithelium) change the bacterial balance in the intestine (intestinal flora). Undigested, they promote the multiplication and consequently the overproduction of certain intestinal bacteria, especially E. coli (Escherichia coli).

What influence do lectins have outside the gut?

Furthermore, there are interactions with enzymes, which lead to deteriorated digestion of proteins. Undigested lectins can get into the bloodstream and thus to other internal organs by binding to cells of the intestinal wall. This leads to changes in the affected organs and the metabolism. This creates restrictions on the body's own immune functions as well as the growth potential. It should be emphasized that most of the studies were done with concentrated and isolated lectins. In our diet, however, they occur in much lower concentrations and always in combination with other nutrients. The results of these studies can therefore not be transferred directly to lectins in our diet. The lectins PHA (phytohemagglutinin) and WGA (wheat germ agglutinin), which are found in raw kidney beans and wheat germ, are particularly well researched. However, we eat kidney beans when cooked. This makes the lectins it contains harmless.

What are the symptoms of lectin poisoning?

When people are exposed to a high concentration of active lectins, acute poisoning occurs. This usually only happens with insufficient processing and subsequent consumption, for example of raw kidney beans and the toxic lectin PHA contained therein. The following symptoms are typical of acute poisoning:

  • Nausea
  • Flatulence (meteorism / bloating)
  • Vomiting
  • Diarrhea

Are lectins associated with autoimmune diseases?

When healthy, the intestine has a barrier. This prevents insufficiently digested molecules or pollutants from penetrating the intestinal wall and entering the bloodstream. Lectins cause changes in the intestinal wall. This disrupts the integrity and function of this barrier. If molecules that are harmful to the small intestine are repeatedly consumed, this leads to increased permeability of the intestinal wall (seeping bowel syndrome, leaky gut syndrome). This is how lectins get into the bloodstream. Once the undigested molecules are in the blood, they bind to other tissue cells and foreign substances (antigens). This connection in turn triggers an immune reaction against the lectins themselves and against the tissues to which they are bound. This can lead to an autoimmune disease.

Do lectins have positive properties?

Yes, lectins can be useful. With inflammatory bowel diseases, it can be useful to bypass the digestive tract and feed the patient intravenously. A direct supply of nutrients via the bloodstream (parenteral nutrition) can calm the gut. This is useful, for example, for acute episodes of Crohn's disease and ulcerative colitis. However, this can lead to a loss of function of the small intestine mucosa (mucosal atrophy). This loss of function means that nutrients are no longer effectively absorbed through the intestinal wall. Lectins can now bind to cells in different intestinal regions and lead to a renewal of the intestinal wall. This prevents or improves a loss of function.

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What foods contain lectins?

Most plant foods contain lectins. Some known examples are listed in this table.

Food groups Lectin Food
Legumes Phytohemagglutinin (PHA) Red kidney beans
Soybean agglutinin (SBA) and Soybean lectin (SBL) Soybeans
Broad bean agglutinin, Vicia faba agglutinin (VFA) Field beans

Vulgaris leukoagglutinin

Green beans
Concanavalin A (ConA) Jack beans
Cicer arietinum agglutinin (CAA-I and CAA-II) Chickpeas
Lens culinaris lectin (LCL) Lentils
Pisum sativum agglutinin (PSA) Peas
Peanut lectin (PNA) Peanuts
Grain Wheat germ agglutinin (WGA) Wheat (wheat germ)
Rice bran agglutinin (RBA) Rice (rice bran)
Corn coleoptile lectin (CLL) Corn
Nightshade family Solanum tuberosum lectin (STL) Potatoes
Lycopersicon esculentum lectin (LEL, TL) Tomatoes
Fungi Pleurotus ostreatus lectin (POL) Oyster mushrooms
Agaricus bisporus agglutinin (ABA) White mushrooms
Garlic Family Allium sativum lectin (ASA I and ASA II) Garlic
Allium cepa agglutinin (ACA) Onions
Fruit Banana lectin (BanLec-I) Bananas

Should I avoid foods containing lectins?

For the majority of the population it is very clear: No, because many of these foods are very healthy for humans. In addition, most lectins are harmless for humans With regard to toxic lectins (for example PHA from raw kidney beans) the following applies: With proper preparation they are harmless to humans, because most of them are not heat-resistant. So if these foods are sufficiently cooked before consumption, they change their structure and are rendered harmless. Their concentration in foods is also reduced if they are soaked, germinated or fermented before consumption. For example, the lectin content of legumes during fermentation is reduced by up to 98 percent. These foods are therefore harmless to the healthy population and should not be eliminated from the diet due to their lectin content.

In some people with autoimmune diseases or rheumatoid arthritis, avoiding foods containing lectin leads to an improvement in symptoms. Legumes cause problems for some people with inflammatory bowel disease, and scientists suspect that lectins also play a role in food intolerance. In this self-test, you can find out first about whether you suffer from intolerance.

Lectins and celiac disease

There is also discussion of whether they are relevant in the development of celiac disease. Nevertheless, studies conducted on humans are missing in order to make a clear recommendation in this regard. Animal studies are usually done with much higher amounts of lectin and higher concentrations than are found in human nutrition. Therefore, their results cannot be directly extrapolated to humans. For this reason, the possible lectin-celiac association is mostly rejected. Because lectins are found in a large amount of healthy foods, they are unlikely to have a significant impact on the development of diseases.

How do I find out if lectins can be problematic for me?

Lectin specific antibodies in the blood can be another indication that there is an increased immune response. The antibodies Immunoglobulin G (IgG) and Immunoglobulin A (IgA) are important here. Keeping a food diary is recommended in any case. The notes can be used to more precisely narrow down foods that cause symptoms to increase. This is how you can find out whether lectins cause problems.

We at Cara Care will be happy to help you and advise you as part of our nutritional therapy program free of charge and from your home. Up to 5 sessions will be reimbursed by your health insurance in Germany.

How is the lectin content of food determined?

The concentration in food is determined by the antibody-based detection method ELISA (enzyme-linked immunosorbent assay). First, a microtiter plate is coated with antigens (in this case lectins). Lectin-specific antibodies are then added and the binding of the antibodies to active lectins is measured.

Are lectins also used in other areas?

In medicine they are used for blood type determination. They can bind to carbohydrates and glycoproteins. This ability is useful for the development of drugs that are supposed to bind to specific cells in the body. Mistletoe lectins (Viscum album L.) inhibit the growth of tumors. Because of this property, they are used to support cancer therapy. In addition, they stimulate the immune system through the improved production of cytokines and natural killer cells. The latter are responsible, among other things, for recognizing and killing tumor cells. An example of this is the drug lectinol, which improves the general quality of life and the tolerance of conventional cancer therapies. They can also be relevant for the therapy of cardiovascular and metabolic diseases as well as for fighting HIV.

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Dr. med. André Sommer

Dr. med. André Sommer

I’m André, a medical doctor from Berlin. Together with a team of medical doctors, nutritionists and data scientists we empower people to understand digestive issues with our app Cara Care.

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