What are lectins?
Lectins are a type of protein that can bind to cell membranes. They are sugar-binding and become the “glyco” portion of glycoconjugates on the membranes. Lectins offer a way for molecules to stick together without getting the immune system involved, which can influence cell-cell interaction.
Lectins are abundant in raw legumes and grains, and most commonly found in the part of the seed that becomes the leaves when the plant sprouts, aka the cotyledon, but also on the seed coat. They’re also found in dairy products and certain vegetables. While lectin content in food is fairly constant, the genetic altering of plants has created some fluctuations.
Lectins in plants are a defense against microorganisms, pests, and insects. They may also have evolved as a way for seeds to remain intact as they passed through animals’ digestive systems, for later dispersal. Lectins are resistant to human digestion and they enter the blood unchanged.
Why are lectins so important?
Lectins are thought to play a role in immune function, cell growth, cell death, and body fat regulation.
Immune response and toxicity
Because we don’t digest lectins, we often produce antibodies to them. Almost everyone has antibodies to some dietary lectins in their body. This means our responses vary. Certain foods can even become intolerable to someone after an immune system change or the gut is injured from another source. The presence of particular lectins can stimulate an immune system response.
There are some lectins that no one should consume. Ever wonder why you don’t see sprouted red kidney beans?
It’s due to phytohaemagglutinin – a lectin that can cause red kidney bean poisoning. The poisoning is usually caused by the ingestion of raw, soaked kidney beans. As few as four or five raw beans can trigger symptoms.
Raw kidney beans contain from 20,000 to 70,000 lectin units, while fully cooked beans usually contain between 200 and 400 units.
While many types of lectins cause negative reactions in the body, there are also health promoting lectins that can decrease incidence of certain diseases. Furthermore, the body uses lectins to achieve many basic functions, including cell to cell adherence, inflammatory modulation and programmed cell death.
What you should know about lectins
Ingesting lectins can cause flatulence. Consuming legumes and grains in their raw form can even result in nausea, diarrhea and vomiting. Indeed, researchers speculate that many apparent causes of bacterial food poisoning may actually be lectin poisoning.
Lectins and the intestinal wall
This GI distress happens because lectins can damage the intestinal lining.
As food passes through the gut, it causes very minor damage to the lining of the GI tract. Normally the cells repair this damage rapidly. Since the purpose of the gut lining is to let the good stuff past and keep the bad stuff contained, it’s important for the cellular repair system to be running at full efficiency.
But lectins can blunt this speedy reconstruction. Our cells can’t regenerate as fast as they need to in order to keep the intestinal lining secure. Thus, our natural gut defenses are compromised after the damage occurs and the gut can become “leaky,” allowing various molecules (including stuff we don’t want) to pass back and forth amid the gut wall. We may also not absorb other important things, such as vitamins and minerals, properly.
When enough lectins are consumed, it can signal our body to evacuate GI contents. This means vomiting, cramping and diarrhea. It’s similar to consuming large amounts of alcohol, which can damage the GI lining and cause GI evacuation.
Lectins and immune response
When lectins affect the gut wall, it may also cause a broader immune system response as the body’s defenses move in to attack the invaders.
Symptoms can include skin rashes, joint pain, and general inflammation. Other chronic disorders may be correlated with leaky gut — for example, researchers have even noted that children with autism have very high rates of leaky gut and similar inflammatory GI tract diseases.
When someone suffers from Crohn’s disease or irritable bowel syndrome, the gut lining seems to be more sensitive to food lectins. This might be due to the high turnover of cells and greater population of the immature variety. These immature cells have plenty of spots for lectins to attach.
The effects of dietary lectins only extend for as long as they are in the body, and the effects can be reduced by eating a variety of fruits, vegetables (rather than high amounts of one type) and foods with beneficial bacteria (e.g., fermented foods).
Lectins and grains
Unrefined grains are more nutritious than refined versions because they contain more nutrients. However, they also provide more lectins (and other anti-nutrients).
While this was likely never a problem when we grew and harvested our own grains, we now have access to MANY whole grain products. Before the invention of modern agriculture, grains were a minor and seasonal crop. Now we can go to the market for 15 minutes and have a cart full of whole grain pasta, bread, rice, quinoa, kamut, amaranth, oats, barley and chips.
The average North American diet is highly grain-based: bread, pasta, rice, cereals, etc. are everywhere, especially in processed foods.
Was the body ever equipped to deal with that type of grain onslaught?
Our ancestors grasped the concept of “survival of the fittest,” and found a solution to the problem of lectins. Soaking, fermenting, sprouting and cooking will decrease lectins and free up the good nutrients. The content of lectins in foods differs year to year and crop to crop.
Grain, cereal, dairy, and legume (especially peanut and soybean) lectins are most commonly associated with reports of digestive complaints. Legumes and seafood are the most abundant sources of lectins in most diets.
How can we reduce or neutralize lectins?
Sprouting seeds, grains or beans decreases the lectin content.
Generally, the longer the duration of sprouting, the more lectins are deactivated. In some cases the lectin activity is enhanced by sprouting (like alfalfa sprouts). The lectins in some grains and beans are in the seed coat. As it germinates, the coat is metabolized – eliminating lectins.
Soaking and cooking
Even wonder why grandma bothered with the long soak, rinse and boil session when preparing beans and grains? Lectin reduction. This is probably the most classic method of preparing beans and grains.
Soak beans and legumes overnight, and change the water often. Drain and rinse again before cooking. Adding sodium bicarbonate (aka baking soda) to the soaking water may help neutralize the lectins further.
Fermentation allows beneficial bacteria to digest and convert many of the harmful substances.
This might be why the healthiest populations stick with fermented soy products like miso, tempeh, tamari and natto. Even some vegetables, such as cabbage, may have fewer antinutrients when fermented. Cultures with a history of grain eating traditionally have used some form of fermentation to treat grains. If you’ve had sourdough bread or beer, you’ve had fermented grains.
Not all lectins are completely destroyed by these methods, and some particularly stubborn lectins in beans remain no matter how lengthy the treatment. Thus, these techniques don’t totally reduce the negative effects for everyone.
Some have argued that since agriculture is a relatively recent invention, humans did not evolve to tolerate grains nor beans well in any case. For some susceptible people, consuming a “Paleo-style” diet, where carbohydrates come from fruits and vegetables, rather than grains and beans, may be beneficial.
Summary and recommendations
Since lectins are so widely distributed in food items commonly consumed by humans, and have been for many centuries, most nutrition experts assume they don’t pose a significant risk to human health.
Still, it does appear that chronic ingestion of untreated high-lectin foods may warrant further consideration. If you consume a diet with plenty of lectin-rich foods, try to reduce the amount by soaking, fermenting, sprouting and/or cooking.
Certain seaweeds and mucilaginous vegetables have the ability to bind lectins in a way that makes them unavailable to the cells of the gut.
Lectins are resistant to dry heat, so using raw legume flours in baked goods should be done with caution.
The “Blood Type Diet” is based on how our blood cells react with lectins in foods.
Some experts hypothesize that it’s no coincidence the top 8 allergens also contain some of the highest amounts of lectins (including: dairy, egg, wheat, soy, peanuts, tree nuts, fish, shellfish).
Some experts theorize that lectins cause urinary tract infections.
Some experts theorize that the reason anemia is higher in developing countries is due to excessive levels of lectin consumption.
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