They’re present in many foods, including whole plant foods. So why are lectins harmful to our health?
Lectins are a type of protein that promote inflammatory responses. This inflammation underlies conditions such Crohn’s disease, systemic lupus, asthma and rheumatoid arthritis.
Lectins were discovered over 100 years ago, and have been found to cause leaky gut and gut dysbiosis.
Despite this, the pressure of popular plant-based diets means that people are eating more legumes and overlooking the damage that lectins can cause the gut. Legumes offer inferior nutrition compared with animal protein, so toxicity needs to be considered when recommending food choices.
Are lectins good or bad?
Lectins are carbohydrate-binding proteins that are difficult to digest. They irritate the lining of the small intestine (known as the brush border), damaging the tight junctions between the small, fingerlike projections that enable us to absorb nutrients.
This damage can lead to leaky gut, contributing to numerous disorders of the gastrointestinal tract, as well as autoimmune diseases. Lectins are also a major contributor to leptin resistance, which contributes to obesity.
Foods that contain lectins
As described in the handbook, Plant Lectins: Properties and Biomedical Applications (John Wiley: 1998), toxin lectins can be found in several foods:
1) Members of the pea family. These include peanuts, pigeon peas, soya beans, kidney beans, mung beans, lima beans, lentils, fava beans, chickpeas, carob, green peas and yellow peas.
Green beans, snow peas and snap peas are also members of this family, but they’re usually well-tolerated once the gut has been healed. This is because they’re immature protein sources with minor amounts of lectins.
2) Grains. These are seeds from grasses, which include barley, oats, rice, rye, millet, wheat, teff, corn, kamut, spelt and possibly wild rice.
Many gastroenterologists believe the detrimental effects of lectins in grains are a factor in the development of Coeliac disease. Genetics and frequent consumption possibly play a critical role in the severity of sensitivities to these foods.
3) Pseudo-grains. These are seeds from broad-leafed plants, such as amaranth, buckwheat, chia and quinoa.
Whereas pseudo-grains were once geographically and seasonally limited, modern agriculture has greatly increased their consumption. This is largely because they can be labelled ‘gluten-free’, since US standards allow any grain with less than 20 parts per million to be called ‘gluten-free’.
What are lectins?
There are several types of lectins, including prolamins and agglutins.
Prolamins are predominantly found in the seeds of plants. They get their name from the high content on the amino acid proline.
Gluten is the most widely known source of prolamins, but studies have also shown that prolamins in quinoa, corn and oats can damage the digestive tract in people with Coeliac disease. Despite this, these grains are frequently included in the ‘gluten-free’ diet.
Agglutinins are found on the seed coating of grains and pseudo-grains. They are named for their ability to cause clumping of red blood cells.
This lectin is used in the bioterrorism agent, ricin. Ricin is the compound in caster beans that’s so toxic, only a tiny amount is needed to cause death.
In the plant, agglutins serve to protect the seed from fungus growth. Genetically modified crops—including wheat, corn and soya beans—have high amounts of agglutinin to ensure high yields.
Should I avoid lectins?
Omitting toxic lectins from the diet, including prolamins and agglutinins, is critical for gut health and other conditions.
As mentioned, lectins are pro-inflammatory and can lead to a leaky gut, which is harmful to both the innate and adapted immune systems.
As few as five soaked, uncooked kidney beans can lead to a gut distress for the raw foodies, while one tablespoon of peanut butter causes peanut agglutinins to enter the bloodstream soon after consumption.
In a study published Lectins and Pathology, 2000, Paolo Zatto and Pamela Zambenedetti from Padua, Italy, researched lectins, microglia, and Alzheimer’s disease. When stained, the microglia (a type of brain cell) of ten Alzheimer’s disease patients were found to be riddled with agglutinins.
Their research concluded that the glycation reaction caused by lectins may be a significant factor in amyloid plaque development. In other words, they may contribute to Alzheimer’s disease.
Bacterial overgrowth & disease
Michèle Mouricout and Bruno Védrine of Limoges, France, described how lectins can cause bacteria to stick to tissues in the intestines, brain, urinary tract, lungs and corneal cells (eye). Their research was reported in Lectins and Pathology, 2000.
This ‘sticking’ of bad bacteria to gut cells can be a critical first stage in the infectious disease process. For this reason, bacterial overgrowth in the gut is associated with a wide variety of diseases, including septicaemia, pulmonary infections and enteropathies.
Lectins have also been implicated in cancer progression. Galectin-3 (GAL-3), a galactoside-binding lectin, is found on the surface of most cancer cells and has been reported to promote the formation of new blood vessels. This provides the tumour with a greater blood supply, enabling it to grow.
Other lectins have been found to cause an excess number of mast cells to gather in the body’s tissues (a condition called mastocytosis), which can be deadly.
Closing thoughts on lectins
Lectins are widely distributed in foods that are consumed daily. After decades of disinterest, biological and medical science is finally waking up to their potential for harm.
The higher the levels of GMO food in the diet, the more lectins are consumed. Without food labelling of GMOs, consumers will continue to be misled and sick.
It’s time we took a closer look at the lectin levels in foods, customizing an individual’s diet for lectin sensitivity to better manage inflammation and autoimmune disease.
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The London Clinic of Nutrition is a multi-disciplined health practice offering personalised nutritional medicine and naturopathy using the functional medicine approach.
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