LEGUMES AND ANTINUTRIENTS
In this post I will try to explain in a very simple and basic way what the antinutrients present in legumes, cereals and seeds are, how they can affect our health and what we should do to consume them in a safer way.
What are antinutrients?
Antinutrients are defined as “natural or synthetic compounds that interfere with the absorption of nutrients”.
They are substances naturally present in plants, plants generate them as a defense, for the survival of the species.
If the seeds are consumed by animals, because they contain these antinutrients, they cannot be digested, so they are excreted and germinate again.
Legumes, cereals and seeds contain antinutrients of different types and in different quantities, it is important to know them, in order avoid their possible adverse effects.
Legumes, nuts, seeds, cereals, and many vegetables are foods that contain antinutrients.
Which commonly consumed foods contain antinutrients?
Some examples are:
- Legumes: lentils, chickpeas, beans, broad beans.
- Nuts: almonds, walnuts, cashews, peanuts.
- Cereals and pseudocereals: rice, oats, quinoa.
- The seeds: flax, sesame.
Main antinutrients:
– Phytic acid:
On the one hand, we know that it blocks the absorption of minerals in the intestine, which could result in deficiencies in them.
It acts by forming complexes that sequester minerals such as iron, zinc, magnesium or calcium.
This problem is not such in advanced societies where a varied diet more than compensates for possible deficiencies.
The problem could be in underdeveloped or developing countries where these nutritional deficiencies are not met and can pose a public health problem.
Phytic acid also has its positive side, it is an antioxidant and helps control blood cholesterol levels.
But at the same time, later studies showed that its consumption can be beneficial, phytic acid is an antioxidant, it prevents osteoporosis.
It also helps reduce blood cholesterol levels and is believed to It can prevent colon cancer.
It is very present in nuts, cereals, legumes and seeds. It should be noted that it is not inactivated by heat.
Soaking it for at least 12 hours before cooking eliminates 60% of it.
– Cyanogenic glycosides or heterosides:
These substances are secreted by some plants as a defense mechanism; they are found in fabaceous or legume plant species1 (also in other species such as Rosaceae and Linaceae, for example).
They are considered an antinutritional factor because they are degraded by an enzyme in the plant itself and give rise to hydrocyanic acid (HCN)2, which in turn decomposes into cyanide and acetone.
HCN is an inhibitor of the respiratory chain and an ingestion of 100 grams of a raw seed that contains it, could be lethal especially in the case of children and the elderly.3
– Saponins:
Saponins are considered antinutrients because they cause hemolysis or destruction of red blood cells, although the degree of toxicity depends on the type of saponins and the sensitivity of the receptor, which is considered low in mammals.
Even so, scientific studies reveal that “the absorption of iron (Fe) decreases when the concentration of saponins increases”4.
They are also attributed a negative effect on the absorption of nutrients, because they affect cholesterol levels in the liver and blood5.
Saponins are responsible for the appearance of foam when we wash quinoa or cook some legumes.
It is believed that they may affect the intestine and promote inflammation, but their toxic effect when ingested orally is doubtful.
Quinoa and soybeans are rich in saponins, soaking and washing them well helps to eliminate them, cooking also helps.
When we consume already cooked and canned legumes, it is also important to wash them very well and always discard the water, the foam that appears is partly due to saponins.
Did you know that potatoes also contain saponins?, especially in the green parts, so make sure to remove them and cook them peeled. Interestingly, sweet potatoes do not contain saponins.
– Tannins:
They are polyphenols, their negative effect is due to their ability to form complexes with proteins and other macromolecules such as starch, thus reducing the nutritional value of food.
They can cause damage to the intestinal mucosa and hinder the absorption of iron, vitamin B12 and glucose.
It has been shown that heat treatment of legumes, cooking, significantly reduces the amount of tannins they may contain.6
Tannins are antinutrients due to their ability to block the absorption of some nutrients, but they also have effects beneficial.
But on the other hand, you’ve probably also heard of their beneficial effects. Tannins are found in grapes, and consequently in wine. We also find them in pomegranates and medlars.
What do these fruits have in common? Their flavor has a rough, bitter touch that is precisely due to tannins.
Coffee, tea, and chocolate also contain them.
As I said, they are polyphenols with antioxidant effects; they are astringent and anti-inflammatory. They also reduce LDL cholesterol levels because they inhibit its absorption.
In plants, tannins also have a protective function against fungi and bacteria. Some of those that contain large quantities of them are strawberries, blueberries (both leaves and fruit), and blackberries.
And as a curiosity, it is interesting that the inner wood of the trunks of many trees is rich in tannins that protect them from microorganisms, thus preventing possible collapse.7
– Oxalates:
Wheat germ and nuts are foods with a high oxalate content, this substance is found in many foods of plant origin and is characterized by inhibiting the absorption of calcium, but they are easy to eliminate with cooking.
Spinach, for example, contains them, cooking them eliminates them, but if from time to time you want to consume them raw, remember not to do so with foods rich in calcium.
Eliminating antinutrients or reducing their effect is quite easy, soaking and cooking are two techniques that help.
How to eliminate antinutrients in the foods we eat?
To eliminate or reduce antinutrients in frequently consumed legumes and cereals, there are a series of techniques that have been applied since ancient times to eliminate them or at least reduce their effect. The most common are:
- soaking
- cooking
- germination
- fermentation
But not all antinutrients that I have named react in the same way to these techniques, for example, phytic acid is not eliminated with temperature, cooking is not enough, it is advisable to soak nuts and legumes for hours and discard that water before consuming them.
Many vegetables contain antinutrients, spinach and cruciferous vegetables are a good example.
Goitrogenic substances, on the other hand, reduce the absorption of iodine from the diet and are present in cabbage, cauliflower, broccoli, turnips… although their activity is reduced by cooking. High consumption of these vegetables with a diet low in iodine could cause goiter due to hypothyroidism.
Don’t be afraid to consume any of these foods, to avoid any adverse effects, in addition to following the recommendations regarding soaking, washing, cooking techniques, etc., have a balanced diet, and consume legumes, seeds, cereals and vegetables in a varied way, without abusing any specific food.
I hope you liked this post and that you find the information interesting.
Cheers! 😉
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1 Cyanogenic Glucoside https://es.wikipedia.org/wiki/Gluc%C3%B3sido_cianog%C3%A9nico
2 Healthy Belly Blog https://www.barrigasana.com/receta-cinco-tipos-de-hummus/
3 Nutrition at 6 Blog http://nutricionalas6.blogspot.com/2016/04/elige-bien-tu-comensal-hoy-con.html
4 British Journal of Nutrition, Cambridge University. The effect of three types of saponin on iron and zinc absorption from a single meal in the rat. https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/the-effect-of-three-typ es-of-saponin-on-iron-and-zinc-absorption-from-a-single-meal-in-the-rat/5FF633A9799303163953DFCCB396A02E#
5 British Journal of Nutrition, Cambridge University. A mechanism for the hypocholesterolaemic activity of saponins. https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/mechanism-for-the-hypocholesterolaemic-activity-of-saponins/5AAB00C1253B27EDD18BBECC1D58FBB0
6 Martínez, MªPaloma. PROTEIN ANTINUTRIENTS FROM LEGUMES: TYPES, TOXICITY AND PHYSIOLOGICAL EFFECTS, page 21. https://uvadoc.uva.es/bitstream/10324/18140/1/TFG-M-N533.pdf
7 Tannin. https://es.wikipedia.org/wiki/Tanino
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