I was calmly reading about boozing in keto when my wife, who was writing an article at the time, asked me for a synonym of a word. To my utter shock and childhood vindication, she told me that legumes have something called anti-nutrients.
What?! I asked her incredulous. You mean to say that legumes are not nutritious? No. Apparently they are not. Or are they?
What are anti-nutrients?
Let’s begin with the definition given by Peumans and Van Damme (1):
“The term “anti-nutrients” suggests what they are. Whereas nutrients are substances that nourish plants and animals to grow and live, anti-nutrients earn their title because they can block the absorption of nutrients. Anti-nutrients are naturally found in animals and many plant-based foods. In plants, they are compounds designed to protect from bacterial infections and being eaten by insects.”
OK, so anti-nutrients are substances found in food that, instead of becoming building blocks for your body, steal away those bricks and the mortar, but only the bad ones. Well, not quite.
Anti-nutrients actually prevent the absorption of certain types of nutrients, many of them quite essential ones, without any regard of how much the body actually needs these nutrients.
Examples of anti-nutrients and the foods that contain them
There are several compounds in the foods we eat classified as anti-nutrients. Examples include:
- Glucosinolates are found in cruciferous vegetables such as broccoli, Brussels sprouts and cabbage. They can prevent the absorption of iodine, which in turn may interfere with thyroid function, even causing goiter.
- Lectins are found in legumes such as beans, peanuts (yes, peanut is a legume), soybeans and whole grains. Lectins can interfere with the absorption of calcium, iron, phosphorus, and zinc.
- Oxalates are found in green leafy vegetables and tea. They can bind to calcium and prevent it from being absorbed.
- Phytates (phytic acid) are found in whole grains, seeds, legumes and some nuts. Phytates can decrease the absorption of iron, zinc, magnesium, and calcium.
- Saponins are found in legumes and whole grains. They can interfere with the normal absorption of general nutrients.
- Tannins are found in tea, coffee and legumes. Tannins can decrease iron absorption.
So, are vegetarians doomed?
Personally, as a (semi) carnivore, I would say yes, but I would be wrong. The truth is, we don’t know. It is not known how much nutrient loss occurs in our diets because of anti-nutrients. Also, the effects vary among individuals based on their metabolism and how the food is cooked and prepared as anti-nutrients like phytates, lectins and glucosinolates can be removed or even deactivated by soaking, sprouting, or boiling the food before eating.
Studies (2) on vegetarians with diets containing high quantities of anti-nutrients (vegetables…) surprisingly do not show deficiencies in iron and zinc for the most part, so the body may be adapting to the anti-nutrients by increasing the absorption of these minerals in the gut.
Bear in mind that several studies proved that some anti-nutrients may even be good for your health. Phytates, for example, have been found to lower cholesterol, slow digestion, and prevent sharp rises in blood sugar (3). Many anti-nutrients have antioxidant and anticancer actions (4), so avoiding them entirely might be a bad idea.
Next time you hear someone claiming that meat is bad for you, remember them that vegetables are anti-nutrients!
1 Peumans WJ, Van Damme EJ. Lectins as plant defense proteins. Plant physiology. 1995 Oct; 109(2):347. http://www.plantphysiol.org/content/109/2/347
2 Stevenson L, Phillips F, O’Sullivan K, Walton J. Wheat bran: its composition and benefits to health, a European perspective. Int J Food Sci Nutr. 2012 Dec; 63(8): 1001–1013. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3507301/
3 Schlemmer U, Frølich W, Prieto RM, Grases F. Phytate in foods and significance for humans: food sources, intake, processing, bioavailability, protective role and analysis. Mol Nutr Food Res. 2009 Sep;53 Suppl 2:S330-75. https://wiebaktmee.nl/cms/pdf/Schlemmer%20_Mol_Nutr_Food_res_2009_Phytate_in_foods_and_significance_for_humans.pdf
4 Stevenson L, Phillips F, O’Sullivan K, Walton J. Wheat bran: its composition and benefits to health, a European perspective. Int J Food Sci Nutr. 2012 Dec; 63(8): 1001–1013. And Liu Z, Luo Y, Zhou TT, Zhang WZ. Could plant lectins become promising anti-tumour drugs for causing autophagic cell death? Cell Prolif. 2013 Oct;46(5):509-15. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3507301/
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