The most common legumes are soybeans, beans, lentils, and peanuts. Many legumes are highly toxic when uncooked. The raw beans can kill mice in two weeks when administered in an amount equal to 1% of the diet. Many of these toxins may be removed during cooking, but not all. Imports of red beans in South Africa were once (legally) prohibited for potential toxicity in humans.
Legumes are similar to cereals. As a grain, legumes are eaten by herbivores, and for this they have developed toxins to protect themselves from mammals, including humans. The main toxins in legumes include lectins and alpha-amylase inhibitors (also present in cereals).
Here are some of the toxic effects of legumes:
- Increased intestinal permeability (leaky gut), indigestion, diarrhea, and bloating. The beans make the intestines of mice permeable, allowing bacteria and toxins to enter the body. The lectin phytohaemagglutinin in beans blocks the production of acid in the stomach, preventing proper digestion, especially of proteins.
- Retarded growth and contraction of the organs. The mice that were given the lectin alpha-amylase legumes suffered from indigestion and had retarded growth.
Administering soybean to mice causes an alteration of the organs- “the pancreas was significantly heavier and lighter than the liver in mice fed the soybeans. The bean with lectin phytohemagglutinin given to human volunteers resulted in the contraction of the gallbladder, two-thirds of the natural size.
The typical effects of the toxicity of legumes include reflux and bloating, but if not cooked enough, the reactions can be much more severe.
The anti-nutrient vegetables
The list of anti-nutrients found in legumes, beans, and soy contains lectins, saponins, phytates, polyphenols such as tannins and isoflavones, protease inhibitors, oligosaccharides of raffinose, cyanogenic glycosides and flavonoid glycosides.
Although the anti-nutrients in beans probably contribute to the effects of poisoning, animal experiments indicate that a special lectin (phytohemagglutinin) present in all varieties of Phaseolus Vulgaris is the real cause. The experiments on human tissues reveal that phytohemagglutinin and other lectins can increase intestinal permeability (leaky gut). Intestinal permeability is one of the first steps towards immune diseases. A compromised intestinal integrity produced by the lectins of the diet can also cause low levels of inflammation, a precursor in the development of atherosclerosis and cancer. In addition to the species “Phaseolus vulgaris”, soy and peanut lectins are known to cause increased intestinal permeability.
The more lectins/ saponins ingested, the greater the damage. The main threat of saponins is to increase intestinal permeability, allowing toxins and gut bacteria to interact with the immune system (due to heart disease and cancer). The other problem lies in the fact that even cooking the vegetables for two hours, 85 to 100% of saponins will not be removed.
Inhibit the absorption of iron, zinc, calcium, and magnesium in legumes and cereals, causing nutritional deficiencies. Cooking the vegetables does not seem to have much effect on phytates, whereas sprouting and fermentation seem to reduce its effects.
- Polyphenols: tannins, and isoflavones
Polyphenols are antioxidants that protect the plants from the sun, insects, and other organisms. The tannins are similar to phytates: they reduce the digestibility of protein and impede the smooth absorption of iron and other minerals. The tannins damage the intestine, increasing intestinal permeability. Isoflavones act like female hormones. Some concentrated isoflavones in soy are called phytoestrogens and can cause goiter, an enlarged thyroid gland, especially if iodine levels are low. In a study by Dr. Ishizuki, it was shown that in subjects 61 years (average age), daily administration of 30 grams of soy for 3 months, resulted in symptoms of hypothyroidism, malaise, lethargy, and constipation. Half of the subjects developed goiter. In a 2007 survey, Dr. Gustavo Roman indicated that soy isoflavones had a risk factor in the development of autism, due to its ability to impair the normal iodine metabolism and thyroid function.
- Protease inhibitors
When we eat any kind of proteins, enzymes break down proteins into amino acids in the intestine. These enzymes are called proteases and must operate normally for proper assimilation of proteins. Practically all legumes contain an anti-nutrient called protease inhibitor, which prevents the intestine enzymes from breaking down proteins. This is partly why the bio-availability of proteins of legumes is very small compared with meat protein. In animal experiments, the ingestion of protease inhibitors depressed the growth and caused an enlargement of the pancreas.
- Oligosaccharide of raffinose
Almost all vegetables contain complex sugars which are responsible for the formation of gas in the intestines. Intestinal enzymes break down these complex sugars into simple sugars, and gut bacteria metabolize these oligosaccharides in different gases such as hydrogen, carbon dioxide, and methane. Depending on the bacterial flora, the symptoms can vary from person to person. In addition, legumes belong to the foods that are high in FODMAP, which contain a type of carbohydrate that can cause digestive problems in some people that are particularly susceptible.
- Cyanogenic glycosides
When digested, these compounds are transformed into deadly prussic acid in the gut. Fortunately, by cooking legumes, most of this compound is destroyed. But the problem does not end here. When cooked, a large portion of hydrogen cyanide is converted to thiocyanate, which together with the soy isoflavones, is an anti-nutrient that weakens the metabolism of iodine, causing goiter.
- Flavonoid glycosides
Consumption of fava beans can be fatal in people with a genetic defect called G6PD. There is a simple blood test to be sure of this deficiency. The consumption of these beans in genetically susceptible individuals can lead to hemolytic anemia. Although it is not completely clear how the consumption of fava beans cause favism, anti-nutrients found in these vegetables are, most likely, the real culprits.
In conclusion, with some precautions (sprouting, fermentation, and baking for a long time) the damage from the consumption of legumes can be reduced but not eliminated altogether, particularly with regard to the consumption of soy and peanuts. But the most important thing to know is that legumes are generally lower in terms of nutrition and bio-availability (both proteins and minerals) compared to foods such as meat, fish, fruit and vegetables. In short, from whatever perspective you have on this, legumes are not part of the Paleo diet.