Soy, pulses, cereals and vegetables: our plant foods contain numerous small substances that protect them from predators. Some of these substances can be harmful to the human digestive tract and thus to the entire metabolism. The effects can be felt through acutely noticeable symptoms of specific micronutrient deficiencies to leaky gut syndrome. However, not every antinutrient harms us and there are ways to prepare food in such a way that the small substances are rendered harmless.
What are antinutrients?
Antinutrients belong to the group of secondary plant substances. This means that they are not macro- or micronutrients like carbohydrates, fats, proteins, vitamins, trace elements or alcohol. Nevertheless, they are the smallest components of the respective plant and have a function: they protect the plant from predators and pathogens such as bacteria and fungi. They are, so to speak, natural pesticides. They can inhibit enzymes of the attackers and thus destroy them. When we humans ingest these substances via the plants in our food, we are not killed, but enzymes can also be stopped in our intestines and inflammation can be triggered.
Anti-nutrients are mainly found in legumes and whole grains in larger quantities, but they are also found in vegetables.
Legumes and antinutrients
At first glance, pulses always seem to have a good nutritional profile, as they have a high protein content, are very filling and are also popular as a meat substitute. However, they contain many of the secondary plant substances that are problematic for us, and in high doses. A high number of such substances is intolerable for our intestines1.
Besides cow's milk and gluten (which could also be counted as anti-nutrients), common irritants include lectins, phytates, saponins, trypsin, oxalic acid and isoflavones. These substances are found in larger quantities in whole grains and legumes such as beans, chickpeas and lentils, but also in smaller quantities in nuts. Peanuts belong botanically to the legumes and also have a higher content of lectins. The primary issue with these plant components, as mentioned earlier, is the following: They inhibit important enzymes in our digestive tract, which on the one hand can lead to inflammatory reactions at the intestinal mucosa. On the other hand, the absorption of numerous micronutrients is reduced or completely blocked1.
It is important not to have a black and white manner or thoughts here and the microbiome in the digestive tract is so complex that not every one of these substances has a serious effect on digestion in every person. Some intestines have adapted well to these foods and, depending on their genetic origin, the substances are less or more problematic. This can also change over the course of a person's life, because the intestines and the entire metabolic system also change with ageing and lifestyle adjustments.
Lectins are found in various whole grains, legumes such as soy, lentils, beans or peanuts and in small amounts in tomatoes, cucumbers and pumpkin. They can trigger headaches and gastrointestinal complaints, vomiting and diarrhoea. Especially if the respective foods are eaten raw, the lectins are very problematic. It can even be dangerous if lentils or beans are eaten raw. They can be partially destroyed by heat, i.e. by cooking the food. If pulses and co. are soaked in water and a dash of lemon juice for 8-12 hours and then rinsed well and then still cooked, the lectins are most successfully removed.
Wheat germ lectin is very heat-stable and is only destroyed during fermentation, so only sourdoughs are practically lectin-free1.
Phytate is found in legumes, in small amounts in some nuts and golden linseed, but especially in very significant amounts in soy and whole grains. The problem is that these phytates bind micronutrients such as calcium, iron, magnesium, copper and zinc from food and thus prevent the absorption of these substances in the intestine1. Thus, these nutrient robbers can promote micronutrient deficiencies. In addition, they inhibit digestive enzymes and thus interfere with optimal digestion1.
Wheat bran has often been promoted as being very rich in iron - which is true in theory. In practice, however, the iron ions cannot be absorbed because the phytic acid in wheat binds them and thus does not release them for absorption. So the micronutrient is simply excreted again. Again, fermentation and soaking of foods is an aid to reducing phytate levels in the diet. When taking supplements containing the micronutrients mentioned, care should also be taken that they are not taken together with foods containing phytic acid.
Trypsin is found in wheat, rye, barley, kamut, spelt, emmer, soy, buckwheat, millet, teff and einkorn. This anti-nutrient inhibits enzymes that break down starch, which can produce toxic substances in the intestine. Fermentation can partially break down trypsin, which again makes sourdough the better option1.
Saponins are found in spinach, beetroot, asparagus, green beans, soy, green tea leaves, peanuts and sugar beet, among others. These substances can promote haemolysis, a process that can shorten the life of red blood cells3. Heating foods greatly reduces saponins, and the vegetables mentioned for this purpose contain important micronutrients and dietary fibre, which is why they are safe when cooked. The problem with green tea is also eliminated by boiling the tea.
Oxalic acid belongs to the oxalates and is found in whole grains, spinach, beetroot, chard, rhubarb, nuts, cocoa, sorrel and black tea. It can promote an increased tendency to blood clotting disorders and urinary stone formation1. For people who have or have had kidney or urinary stones, foods with oxalic acid are taboo. For all others, this plant substance is mostly unproblematic and can be largely dissolved by blanching, cooking and heating anyway1.
Isoflavones are another secondary plant substance form. Especially the phytoestrogens are problematic here, because they dock onto the oestrogen receptors. Even though they are not oestrogens in the chemical sense, they have an oestrogen-like effect. So they are very problematic because they interfere with the hormone system and in today's world oestrogen dominance is already widespread anyway (due to contraceptives like the pill, microplastics and other environmental changes). Phytoestrogens are found in large quantities in soy and all soy products and in somewhat smaller quantities in wine and beer. Soy in particular should usually be avoided for this and other reasons.
The problem with soy
It is not difficult to see that almost all antinutrients have a common denominator, namely the soybean. In summary, it contains saponins, trypsin, phytates, lectins and phytoestrogens, and all of them in considerably high quantities. This is one of the reasons why it can be grown cheaply in monocultures, because it is very resistant to predators and parasites with all these protective substances. However, it is not beneficial for our digestive tract and hormonal system and can thus worsen our intestinal health, inhibit the absorption of important micronutrients and promote oestrogen dominance.
While the bean is indeed very high in protein, it has many of the anti-nutrients mentioned above, is usually contaminated with heavy metals from washing in special tanks, may be genetically modified and also contains phytoestrogens. These are substances that act on our oestrogen receptors and thus upset our hormone balance. If soy is still being considered, the slightly more optimal source would be tempeh, as this product is better tolerated due to the special fermentation process.
Soy is a promoter of inflammation due to its omega-6 fatty acids and is also often contaminated with heavy metals that trigger further inflammatory processes in the organism. Even though soy has a high protein content, the aforementioned anti-nutrients inhibit the protein-cleaving enzymes, which is why the bioavailability of soy protein is not a good value2.
The additional goitrogens contained in the soybean can cause the enlargement of the thyroid gland, as they inhibit the iodine uptake in the thyroid gland. As a result, the thyroid gland can no longer produce its hormones in sufficient quantities3. Thus, in addition to phytoestrogens, soy contains another substance that can upset the hormone system. It remains to say that there are also exceptions here and some people tolerate soy in smaller quantities. If this is the case, only fermented soy products such as tempeh are recommended, because the fermentation process also removes some of the anti-nutrients.
Legumes and antinutrients and the exeption of peas
Like soybeans, most legumes contain a higher number and larger amounts of anti-nutrients. This is why they should be avoided for the time being during intestinal rehabilitation. These include chickpeas, lentils, beans and peanuts. Those who tolerate them better in the long term due to genetic and microbial reasons should always soak them as described above, rinse them well and be sure to cook them.
Green peas and green snap beans are the exception here: although botanically they belong to the legumes, they contain only very small amounts of the anti-nutrients mentioned. By the way, the green pea is the unripe version of the yellow pea, which when ripe contains higher amounts of antinutrients such as phytoestrogens. Green peas are also relatively high in protein for a vegetable (5-8g/100g).
There are many phytochemicals besides nutrients that can be potentially problematic for our gut and. However, this does not mean that we should no longer eat any of these plants, but rather that we should listen individually to what possible reactions our body has to these foods. Since legumes, especially soy and also grains contain antinutrients in high amounts, caution should be exercised especially with these foods. Those who need to regenerate their intestinal mucosa (more on this topic at the blog article about the the Leaky Gut Syndrome) should completely avoid these plants for three months. After that, however, individual research can be done to see whether one can tolerate fermented products such as sourdough bread or, under the soaking conditions described, legumes. The goal should always be to get to know one's body exactly and thus decide which foods one should eat. The human organism is too complex to say that the same diet is right for everyone.
1 Frankenbach, Thomas (2021): Dein innerer Ernährungsberater - Wie wir mit somatischer Intelligenz mehr erreichen als mit jeder Diät. Berlin: Audible Studios.
2 Sotelo-Lopez, A.; Hernandez-Infante, M.; Artegaga-Cruz, M. E. (1978): Trypsin inhibitors and hemagglutinins in certain edible leguminosae. In: Archivos de investigacion medica 9 (1), S. 1–14.
3 Doerge D. R., Sheehan, D. M.: “Goitrogenic and estrogenic activity of soy isoflavones”. Environ Health Perspect, Juni 2002; Vol. 110 (3), S. 349-53