Lectins, dangerous for health or not?

Hi, this is Galit Goldfarb, nutritionist, and medical scientist. Welcome to my blog where you will find great articles to help you transform your health quickly through practical lifestyle changes based on science. My articles will guide you, step-by-step, to lasting weight loss and better health for you and your family no matter your current situation.

Today I will talk about lectins and determine, through scientific evidence, their effects on our health and what we can do about it.

But, to begin with, what are lectins?

Lectins are a class of carbohydrate-binding protein molecules present throughout nature in animals, plants, and microorganisms. Lectins are found in most plant foods but higher concentrations are found in legumes, tubers, grains, and potatoes.

The five foods that contain the most lectins are:

•    Grains, especially processed grains.

•    Beans

•    Dairy Foods, if the milking animal was fed on grains rather than on grass.

•    Nightshade vegetables

•   GMO foods: Lectins are often added into the DNA of genetically engineered crops to enhance pest and fungal resistance.

Lectins have been found in the foods we eat for over 2 million years.

We would have never made it this far as a species if our bodies could not disable lectins or use them to our advantage (more on this in a moment)

Lectins serve the plant as a protection mechanism that is not dependent on immune function, like our skin serving as a barrier to pathogens.

Lectins bind to the last sugar, the “glyco” section of the carbohydrate chain of glycoconjugates found on cell membranes. Glycoconjugates are carbohydrates covalently linked to other compounds such as proteins, lipids, peptides, etc., to form glycoproteins, glycolipids, glycopeptides, etc., and provide a way for one molecule to stick to another molecule without any immunity involved.

Lectins also participate in recognition of cells on the cellular and molecular level and also mediate cell to cell interactions. Lectins bind to carbohydrates through some relatively weak bonding resembling Velcro; each interaction is relatively weak and permits unlinking when needed but ensures specificity.

Lectins are also produced by our body for cell adhesion which plays a part in the immune response to substances that coat foreign antigens, making them more prone to phagocytosis (the digestion of pathogens by our immune cells), as well as in the prevention of blood cells escaping into the tissues.

Lectins are also antimicrobial, they capture microorganisms through their stickiness, and can also inhibit cancer cells and therefore are also useful for our health.

The hype about lectins being dangerous to our health began in 1999 following a food poisoning that affected a large number of hospital workers after eating a meal containing red kidney beans.

The investigation found no pathogenic bacteria in the food but did find that the beans had very high levels of the lectin phytohemagglutinin.

Another study in the UK looked at the incidence of red kidney bean poisoning between July 1976 and February 1989, where 50 incidents were reported and nine events in which nausea, vomiting, and diarrhea developed within 1-7 h of ingestion of the beans. These events were confirmed to have had high levels of the lectin haemagglutinin in the beans.

The adverse effects of consuming raw lectin rich foods:

Just like other animals, humans are vulnerable to the toxicity of lectins. Concentrated amounts can cause digestive issues and long-term health problems because lectins are not degraded by stomach acid or enzymes, making them virtually resistant to digestion.

Lectins that we get from raw lectin rich foods enter the body, and The stickiness of lectins makes them prone to binding especially on tissues that are very sensitive to their agglutinating effects such as nervous and connective tissue, the intestinal wall and the bladder.

Lectins may eventually damage the gut wall and the tissue to which they attach themselves.

Damage to the gut wall may lead unwanted substances and bacteria to penetrate the gut more easily through lesions caused by lectins allowing them to enter the bloodstream where they can interact with glycoproteins on cell surfaces leading to inflammation or also autoimmune reactions, where the immune system attacks the body’s own tissues.

Lectins may also inhibit the absorption of vitamins.

It is suggested that lectin levels increase in processed grains because by removing the seed coat, which constitutes about 10% of the dry bean seeds, this influences the concentration of lectins on a unit per weight basis [Deshpande et al., 1982].

Disabling Lectins:

Remember I mentioned that we could disable lectins? Well, monosaccharides (simple sugars) and oligosaccharides (short chains of 2-10 sugar molecules) can disable lectins by binding to lectins found in our foods. This binding prevents their attachment to the carbohydrates within the cell membrane and prevents damage to the cell wall.

Solution:

The best way to reduce the adverse effects of lectins is not by avoiding foods rich in lectins but by soaking these foods overnight and then boiling them.

In fact, cooking legumes in water eliminate almost all lectin activity (12, 13).

While raw red kidney beans contain 20,000 to 70,000 hau (hemagglutinating unit) when cooked kidney beans contain only 200-400 hau, a significant difference.

Lentils, on the other hand, do not need more than 10 minutes soak in boiling water before cooking.

The best type of cooking method that also preserves most nutrients in the foods is pressure cooking. Pressure cooking is one of the best ways to inactivate lectins in grains and beans because they reach very high temperatures.

Many cultures also germinate or ferment these foods to improve their digestibility and nutrient value while reducing toxicity.

In fact, gluten proteins are substantially degraded during germination and vitamins C and E, and beta-carotene that are hardly detectable in the dry grains, upon germination the concentrations of these antioxidant vitamins increases significantly.

To summarize: There is no need to remove lectin rich foods including root vegetables, grains, and beans, which are rich in fiber and so many beneficial nutrients, just ensure that you pre-soak them and cook them properly and if possible, also sprout them.

 

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References:

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  2. Jeffrey D Esko and Nathan Sharon (2009) Chapter 34 Microbial Lectins: Hemagglutinins, Adhesins, and Toxins
  3. Carbonaro M, Grant G, Cappelloni M, Pusztai A. Perspectives into factors limiting in vivo digestion of legume proteins: antinutritional compounds or storage proteins? J Agric Food Chem. 2000 Mar;48(3):742-9.
  4. Rhodes JM. Beans means lectins. Gut. 1999;44:593–594.
  5. J. C. Rodhouse, C. A. Haugh, D. Roberts, and R. J. Gilbert. Red kidney bean poisoning in the UK: an analysis of 50 suspected incidents between 1976 and 1989. Epidemiol Infect. 1990 Dec; 105(3): 485–491.
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  9. QiangWang, Lu-GangYu, Barry JCampbell, Jeremy DMilton Identification of intact peanut lectin in peripheral venous blood. The Lancet Volume 352, Issue 9143, 5 December 1998, Pages 1831-1832
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  11. Pusztai, A (1991). Plant lectins. Cambridge University Press, Cambridge, UK.
  12. Grant, G and van Driessche, E. (1993). Legume Lectins. Physiochemical and nutritional properties, Recent Advances in Anti-Nutritional Factors in Legume Seeds. Wageningen Pers.
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