Lectins
All beans and legumes are concentrated sources of lectins. Lectins are potent antinutrients that plants have evolved as toxins to ward off predators. [10] Remember, raw or undercooked kidney beans cause severe cases of food poisoning in humans and were lethally toxic in rats. Although several kidney bean antinutrients probably contributed to these poisonous effects, animal experiments indicate that a specific lectin found in kidney beans was the major culprit. [2, 44] Kidney beans and all other varieties of beans (black beans, kidney beans, pinto beans, string beans, navy beans etc.) within the Phaseolus vulgaris species contain a lectin called phytohemagglutinin (PHA). The more PHA we ingest, the more ill we become. This is why raw beans are so toxic – they contain much higher concentrations of PHA than cooked beans. [4, 23. 46] However, cooking doesn’t completely eliminate PHA, and even small amounts of this lectin are known to produce adverse health effects, providing they can penetrate our gut barrier.
The trick with lectins is that they must bypass our intestinal wall and enter into our bloodstream if they are to wreak havoc within our bodies. So far, no human studies of PHA have ever been conducted. However, in laboratory animals, PHA easily breeches the gut barrier and enters into the bloodstream where it may travel to many organs and tissues and disrupt normal cell function and cause disease. [45, 49] Human and animal tissue experiments reveal that PHA and other food lectins can cause a “leaky gut” and enter circulation. [24, 34, 35, 45, 47, 49, 64, 65] A leaky gut represents one of the first steps implicated in many autoimmune diseases. [67] Impaired intestinal integrity produced by dietary lectins may also cause low level inflammation in our bloodstreams [15, 43, 48, 62] – a necessary step for atherosclerosis (the artery clogging process) and cancer.
Besides kidney beans and other bean varieties within Phaseolus vulgaris species, all other legumes contain lectins with varying degrees of toxicity ranging from mild to lethal. Soybean lectin (SBA) is also known to impair intestinal permeability and cause a leaky gut. [1, 35] Peanut lectin (PNA) is the only legume lectin to have been tested in living humans by Dr. Rhodes’ research group in London. Within less than an hour after ingestion in healthy normal subjects, PNA entered their bloodstreams [64] – whether the peanuts were cooked or not. (Later I will show you how peanuts and PNA are potent initiators of atherosclerosis.)
The lectins found in peas (PSA) and lentils (LCA) seem to be much less toxic than PHA, SBA or PNA, however they are not completely without adverse effects in tissue and animal experiments. [9, 21, 25, 38] Unfortunately, no long term lectin experiments have ever been conducted in humans. Nevertheless, from animal and tissue studies, we know that these antinutrients damage the intestinal barrier, impair growth, alter normal immune function and cause inflammation.
Saponins
The term, saponin, is derived from the word soap. Saponins are antinutrients found in almost all legumes and have soap-like properties that punch holes in the membranes lining the exterior of all cells. As was the case with lectins, this effect is dose dependent – meaning that the more saponins you ingest, the greater will be the damage to your body’s cells. Our first line of defense against any antinutrient is our gut barrier. Human tissue and animal studies confirm that legume saponins can easily disrupt the cells lining our intestines and rapidly make their way into our bloodstream. [1, 16, 17, 18, 32] Once in the bloodstream in sufficient quantities, saponins can then cause ruptures in our red blood cells in a process. known as hemolysis which can then temporarily impair our blood’s oxygen carrying capacity [3] In the long term, the major threat to our health from legume saponins stems not from hemolysis (red blood cell damage) but rather from their ability to increase intestinal permeability. [3, 16, 17, 18, 32] A leaky gut likely promotes low level inflammation because it allows toxins and bacteria in our guts to interact with our immune system. This process is known to be is a necessary first step in autoimmune diseases [67] and may promote the inflammation necessary for heart disease and the metabolic syndrome to develop and progress. [68]
The other major problem with legume saponins is that cooking does not destroy them. In fact, even after extended boiling for two hours, 85-100% of the original saponins in most beans and legumes remain intact. [55] On the other hand, by eating fermented soy products such as tofu and tempeh, or sprouted beans you can lower your saponin intake. [39] The table below shows you the saponin content of some common beans, legumes and soy products.
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