Soy, legumes, grains and vegetables: Our plant-based 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 become noticeable through acutely noticeable symptoms of specific micronutrient deficiencies and even leaky gut syndrome. But 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 are secondary plant substances. This means they are not macro or micronutrients such as 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. So they are, so to speak, natural pesticides. They can inhibit the attackers' enzymes and thus destroy them. When we humans ingest these substances through the plants in our food, we are not killed, but enzymes can also be stopped in our intestines and inflammation can be triggered.
Antinutrients are mainly found in large quantities in legumes and whole grains, but they are also found in vegetables.
Legumes and Antinutrients
At first glance, legumes always seem to have a good nutrient 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 phytochemicals that are problematic for us, and in high doses. A large number of such substances are incompatible with our intestines 1 .
Commonly occurring irritants include - in addition to cow's milk and gluten (which could also be considered antinutrients) - lectins, phytates, saponins, trypsin, oxalic acid and isoflavones. These substances are found in large quantities in whole grains and legumes such as beans, chickpeas and lentils, but also in smaller quantities in nuts. Botanically speaking, peanuts are legumes and also have a higher content of lectins. The primary problem with these plant components is, as already mentioned, the following: They inhibit important enzymes in our digestive tract, which on the one hand can lead to inflammatory reactions in the intestinal mucosa. On the other hand, the absorption of numerous micronutrients is reduced or completely blocked 1 .
It is important not to think in black and white terms here and that 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 years, because as we age and through lifestyle adjustments, the intestines and the entire metabolic system also change.
In addition, the antinutrients in legumes and other foods can be reduced through fermentation and soaking processes. For example, if you soak raw, hard chickpeas in cold water with a dash of lemon juice for 8-12 hours, then rinse them well in a sieve several times and only then cook them, they contain a significantly lower proportion of antinutrients. However, these processes cannot be guaranteed when eating out, so it may be helpful to take a high-quality supplement containing digestive enzymes with or before eating.
Lectins
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 cause headaches, gastrointestinal complaints, vomiting and diarrhea. Lectins are particularly problematic if the food in question is consumed raw. 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 legumes etc. are soaked in water and a dash of lemon juice for 8-12 hours and then rinsed well and then boiled, the lectins are removed most successfully.
Wheat germ lectin is very heat-stable and is only destroyed during fermentation, so only sourdoughs are practically lectin-free 1 .
Phytates
Phytate is found in legumes, in small amounts in some nuts and golden linseeds, but above all 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. These nutrient thieves can promote micronutrient deficiencies. In addition, they inhibit digestive enzymes and thus disrupt optimal digestion 1 .
Wheat bran has often been touted as being high 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 therefore does not release them for absorption. The micronutrient is simply excreted again. Here too, fermentation and soaking of food helps to reduce the phytate content in the food. Even when taking supplements that contain the micronutrients mentioned, care should be taken to ensure that they are not taken together with foods containing phytic acid.
Trypsin
Trypsin is found in wheat, rye, barley, kamut, spelt, emmer, soy, buckwheat, millet, teff and einkorn. This antinutrient inhibits enzymes that break down starch, which can produce toxic substances in the intestines. During fermentation, trypsin can be partially broken down, making sourdough the better option 1 .
Saponins
Saponins are found in spinach, beetroot, asparagus, green beans, soy, green tea leaves, peanuts and sugar beets, among others. These substances can promote hemolysis, a process that can shorten the lifespan of red blood cells 3 . Heating food greatly reduces saponins and the vegetables mentioned contain important micronutrients and fiber, which is why they are harmless when cooked. Even with green tea, the problem is eliminated by boiling the tea.
Oxalates
Oxalic acid is one of the oxalates and can be 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 formation 1 . Foods containing oxalic acid are taboo for people who have or have had kidney or urinary stones. For everyone else, this plant substance is usually unproblematic and can be largely dissolved by blanching, cooking and heating anyway 1 .
Isoflavones
Isoflavones are another form of phytochemical. Phytoestrogens in particular are problematic here because they dock onto the estrogen receptors. Even if they are not estrogens in the chemical sense, they have an estrogen-like effect. So they are very problematic because they interfere with the hormonal system and estrogen dominance is already widespread in today's world (due to contraceptives like the pill, microplastics and other environmental changes). Phytoestrogens are found in large amounts in soy and all soy products and in slightly smaller amounts in wine and beer. Soy in particular should usually be avoided for this and other reasons.
The problem with soy
It's not hard to see that almost all antinutrients have a common denominator, soybean. In summary, it contains saponins, trypsin, phytates, lectins and phytoestrogens and all of them in considerably high amounts. 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 therefore worsen our intestinal health, inhibit the absorption of important micronutrients and promote estrogen dominance.
Although the bean actually has a very high protein content, it contains many of the antinutrients mentioned above, is usually contaminated with heavy metals due to washing in special tanks, can be genetically modified and also contains phytoestrogens. These are substances that attack our estrogen receptors and thus disrupt our hormonal balance. If soy is still to be considered, the more optimal source would be tempeh, as this product is better tolerated due to the special fermentation process.
Soy promotes inflammation due to its omega-6 fatty acids and is also often contaminated with heavy metals, which trigger further inflammatory processes in the organism. Even though soy has a high protein content, the antinutrients mentioned inhibit the protein-splitting enzymes, which is why the bioavailability of soy protein is not good 2 .
The additional goitrogens contained in soybeans can cause the enlargement of the thyroid gland because they inhibit iodine absorption in the thyroid gland. As a result, the thyroid can no longer produce enough hormones 3 . In addition to phytoestrogens, soy contains another substance that can disrupt the hormonal system. It remains to be said that there are exceptions here and that some people can tolerate soy in smaller quantities. If this is the case, only fermented soy products such as tempeh are recommended, as the fermentation process also removes some of the antinutrients.
Legumes and antinutrients and the exception of peas
Like soybeans, most legumes contain a higher number and larger amounts of antinutrients. That's why they should be avoided for the time being when cleaning the intestines. These include chickpeas, lentils, beans and peanuts. If you tolerate them better in the long term for genetic and microbial reasons, you should always soak them as described above, rinse them well and definitely boil them.
Green peas and green beans are the exception here: although they are botanically legumes, they only contain very small amounts of the antinutrients mentioned. By the way, the green pea is the unripe version of the yellow pea, which, when mature, contains higher amounts of antinutrients such as phytoestrogens. Green peas are also relatively high in protein for a vegetable (5-8g/100g).
Conclusion
In addition to nutrients, there are numerous secondary plant substances that can potentially be problematic for our intestines. However, this does not mean that we should stop eating these plants, but rather that we should listen individually to what possible reactions our bodies have to these foods. Since legumes, especially soy and grains, contain high amounts of antinutrients, caution should be exercised, especially with these foods. If you need to regenerate your intestinal mucosa (more on the topic of “ Leaky Gut Syndrome ”), you should avoid these plants completely for three months. However, you can then research individually whether you can tolerate fermented products such as sourdough bread or legumes under the soaking conditions described. The goal should always be to get to know your body thoroughly and decide what foods you should eat. The human organism is too complex to say that the same diet is right for every person.
Sources:
1 Frankenbach, Thomas (2021): Your inner nutritionist - How we achieve more with somatic intelligence than with any diet. Berlin: Audible Studios.
2 Sotelo-Lopez, A.; Hernandez-Infante, M.; Artegaga-Cruz, ME (1978): Trypsin inhibitors and hemagglutinins in certain edible leguminosae. In: Archivos de investigacion medica 9 (1), pp. 1–14.
3 Doerge DR, Sheehan, DM: “Goitrogenic and estrogenic activity of soy isoflavones”. Environ Health Perspective, June 2002; Vol. 110 (3), pp. 349-53
