It has always been said that the habit does not make the monk, although sometimes it is difficult to overcome the first impression. In the case of antinutrients, and by virtue of their etymology, it is true that at first sight it can be difficult to overcome the initial rejection – perhaps even fear – of these elements present in many everyday foods. The matter seems simple a priori: if nutrients are something good, and positive, antinutrients, by definition, have to be something bad and negative. The hero and the antihero. There are no more questions, Your Honor. Or are there?
Despite the bad name, there is generally no reason to worry about antinutrients. In fact, in some cases, and despite their negative connotations, the substances that fall into this category are beneficial and even essential as they form part of a whole – the food matrix – that has a net positive nutritional balance. That is why it is worth knowing them in detail.
What are antinutrients?
Antinutrients are substances present in foods that interfere with or block the use of real nutrients. Regardless of whether they are of plant or animal origin – because there are all kinds – many foods contain certain substances that, present naturally, prevent or hinder the use of other nutrients. This blocking action is carried out both on some of the nutrients that are in that food, as well as on the same nutrients that may be found in other foods.
With a few exceptions, most of the antinutrient effects that can be reported occur during the digestive stage, especially at the time of nutrient absorption. That is, in most cases, antinutrients prevent the absorption of certain vitamins and minerals during the process of digesting food.
In other cases, beyond the moment of absorption, certain antinutrients will limit the function of an organ or its function. A classic example is, as will be shown later, the presence of goitrogenic substances in certain foods that limit or hinder the function of the thyroid.
7 antinutrients and how to eliminate them
There are various substances that interfere with the absorption of different nutrients and these are the best known:
Egg avidin, an antinutrient for vitamin B8
Avidin is a protein found in egg white that has a special affinity for biotin or vitamin B8. In this way, avidin binds to the aforementioned vitamin and creates a complex that prevents B8 from being absorbed. It is thought that this disadvantage, a priori, exerts a protective function in the egg itself by preventing the growth of bacteria since bacteria need biotin for their multiplication.
The positive side of the matter lies in knowing that the “perfidious” avidin is denatured by high temperatures so that when we cook the egg it will be deactivated. It is necessary to point out at this point that the consumption of raw eggs always entails a particularly high risk of food poisoning (due to the risk of salmonellosis). Thus, cooking the egg, in addition to sanitizing the food by eliminating possible Salmonella bacteria, produces a double beneficial effect by transforming biotin and eliminating its antinutritional effect.
Oxalic acid, the antinutrient of vegetables
Oxalic acid is naturally present and inherent in many foods of plant origin. Once ingested, it has a double negative perspective:
- On the one hand, during digestion, it can form insoluble salts with various cations (positively charged minerals), preventing them from being absorbed.
- On the other hand, oxalic acid, once absorbed, can also form this kind of complex with the minerals in our body.
The biggest negative aspect in both cases is the formation of calcium oxalate salts. In the first case, the absorption of a certain part of the calcium present in the diet would be hindered, and in the second, calcium oxalate crystals can form which, in the environment of the kidney metabolism, can lead to the formation of kidney stones of this nature. Foods with the highest proportion of oxalic acid are, for example, spinach, beetroot, chard, peppers, cocoa, leeks, grapes, and coffee.
Regardless of the oxalic acid present in our diet, the possibility of forming calcium oxalate kidney stones also depends on interpersonal variability. Thus, it is advisable for all those particularly susceptible people to consider consuming these foods, which, as can be easily seen, also have an unquestionable healthy perspective.
As for the general population, the advice is not to avoid these foods, far from it, but to continue consuming them rationally without resorting to massive doses of foods that are a major source of oxalic acid. Therefore, be careful with some “detox” smoothies (damn expression). In 2016, the European Food Safety Authority (EFSA) published a report on the 18 potential risks derived from the use we make of food, and specifically, risk 14 refers to the pernicious excess of oxalic acid that is easy to access from the use of the so-called green smoothies, so fashionable today. That is, spinach yes, but tons of raw spinach (or similar) all the time, no.
Phytic acid from vegetables, nothing to fear
Phytic acid is very similar to the previous case, which, typically associated with the presence of dietary fiber in many plant foods, is capable of forming insoluble salts (phytates) with a wide variety of mineral cations. In this case, and unlike the previous case, the antinutritional action is only limited to the moment of absorption, such that some minerals would not be available when associated with this compound. This would be the case, for example, of calcium, iron, zinc, or magnesium.
The general advice is, again, to ignore this possible antinutritional effect, since as one might suspect, phytic acid, as an inseparable element of fiber, is a lesser evil in the achievement of a greater good: the consumption of fresh plant-based foods, nuts, whole grains, and legumes, among others.
Legume saponins and their side effects
In the case of saponins, we are referring to a class of substances that have a dual nature: part of their molecule is soluble in water and the other in lipids, in such a way that they can form “soaps” and hence their name ( sapo, from the Latin, soap). Present prominently, but not exclusively, in legumes, this family of substances can have various effects on health depending on each one. In addition to finding some with an eminently toxic character when consumed in large quantities, most of them have a notable chelating effect on minerals at the time of digestion-absorption. In this way and again, they form insoluble complexes with said minerals that make them no longer available to be absorbed.
However, at the same time, there are also various sources that claim that saponins have clearly positive health effects (most of the time exaggerating these effects without further evidence). Thus, it has been said about saponins, I repeat, without much evidence to support these claims, that they reduce cholesterol, that they have an antioxidant effect, and even that they reduce the risk of cancer or that they help in weight loss. Anyway.
Foods that are a source of saponins are, in their vast majority, highly recommended options within a healthy food consumption pattern. And perhaps this is the reason why, in the end, so many properties (out of context) are transferred to these options: chickpeas, soybeans, peanuts, lentils, peas, garlic, ginseng, cassava, etc.
Lectins in legumes and how to inhibit them
Without leaving this recommended group of foods, which corresponds to the legume family, lectins are a series of proteins that are especially abundant in them. Accused without too much evidence of countless evils and undesirable circumstances, the proven fact is that, like all the previous cases, they do have a notable antinutritional character whenever the food that contains them is consumed raw. Thus, it is quite probable that the presence of lectins limits the absorption of certain minerals (calcium, iron, zinc, phosphorus, among others) by forming complexes with them. The most interesting part of the matter is that, like what happens with avidin, these proteins are denatured by heat, in such a way that cooking the foods that contain them inhibits the antinutritional character of the lectins.
Foods with a higher proportion of lectins are most legumes, peanuts, tomatoes, potatoes, eggplant, fruit in general, and also cereals.
Tannins in many foods and their contraindications
Regarding tannins, they are a family of complex polymers that are especially abundant in any food of plant origin (in greater or lesser proportion). In most cases, their mention (“with tannins”) conveys good vibes, and this is true since many of them have a notable antioxidant activity. For this reason, various properties are often attributed to them: antifungal, antibacterial, antitumor, antidiabetic, etc.
If tannins are on this list, it is because, along with the above properties, they also have the ability, like the other companions already mentioned, to “sequester” certain minerals and proteins at the time of digestion. Some of the foods that contain tannins in significant quantities are coffee, tea, grapes (and their derivatives), spinach, pomegranate… On the sensory level, the presence of tannins is highlighted by sensations related to bitterness and “roughness”.
Brassica glucosinolate and the thyroid
Do you recognize the spicy taste or characteristic aroma of certain foods such as cabbage, mustard or radishes? Well, these sensations are due to the presence of a family of compounds, glucosinolates, which in addition to their sensory qualities interfere with iodine metabolism. In general, the group of molecules known by this name, among which progoitrin stands out, are considered goitrogenic substances, that is, they have the capacity to interfere with the physiological use of iodine and thus increase the risk of developing goiter (overgrowth of the thyroid gland), perhaps the most characteristic sign associated with hypothyroidism in adults.
Unlike most of the cases seen up to this point, the main effect of glucosinolates is not exerted at the time of absorption but, through various enzymatic processes, they end up hindering the endogenous use of iodine by the thyroid. This is the reason why people at risk or in a situation of hypothyroidism usually have their intake of this kind of food controlled. Notwithstanding the above, the enzymatic cascade by which glucosinolates end up in this effect can be disrupted when the problematic foods are cooked, since these substances are denatured by the application of heat.
Foods that are a potential source of glucosinolates and which should be consumed raw with special care by susceptible people are all those belonging to the brassica family, also known as cruciferous vegetables: Brussels sprouts, cauliflower, cabbage, collard greens, kale, radishes, mustard, turnips, broccoli, Romanesco, etc.
Nutrient and antinutrient at the same time
Can this diametrically opposed duality be possible? It is. Let us consider the case of all those minerals that use the same channel, the same gateway to the body at the time of absorption. As you can imagine, the number of channels or gateways is limited and when one of them is occupied giving way to a mineral, it cannot be doing so with another. In this sense, at the moment when many of the different minerals “compete” to enter, it can be considered that some mineral nutrients are at the same time antinutrients for other mineral-nutrients, and vice versa. This is the case in certain circumstances as occurs with calcium and phosphorus or with magnesium, or even between calcium and iron.
Antinutrients, are they dangerous?
Several studies have pointed out the negative effects of various antinutrients on health. However, it should be noted that in most cases it would be necessary to consume a large amount of these antinutrients to develop these possible negative effects. In addition, as has been proven, most antinutrients are broken down when food is cooked. Therefore, the risk of suffering some adverse effect from eating these cooked foods should not be a cause for alarm.
In any case, it is worth looking at the food scene as a whole and keeping the microscope off the seemingly catastrophic search for antinutrients. Most foods containing antinutrients – even all of them – are among the best options within the recommendations for a healthy and balanced diet. There is very little doubt in the field of science when it comes to supporting the benefits of a diet rich in fruits, vegetables, legumes, and whole grains. The health benefits of incorporating these foods into the diet far exceed the supposed advantages of avoiding them simply because they contain antinutrients. Thus, most experts in dietetics and nutrition will never put a negative warning sign about avoiding antinutrients, unless all they are looking for is controversy and visibility.