Talking to the readers of this magazine about how nutritious a well-balanced vegan diet is would be preaching to the converted. No doubt that they also already know that there is only one nutrient that we cannot get from a balanced whole foods vegan diet, which is vitamin B12. Other micronutrients that, in some cases, could be slightly tricky to get enough from this diet have already been reviewed in previous editions. As were the ways to combine foods to improve absorption, such as eating vitamin C-rich foods together with iron-rich foods.

The focus of this feature will be on so-called ‘antinutrients’ – what they are, what they do, and how to ‘tackle’ them.

Antinutrients are several compounds found in plants that interfere with nutrient absorption by the human body. (The term gained particular attention from the public after a certain Dr Gundry published his book The Plant Paradox – have a look if you would like to have a good laugh at a particularly elaborated anti-plant scaremongering (1)).

The most common types of these chemicals are phytates, lectins, oxalates, glucosinolates, and a type of polyphenols, called tannins. Plants synthesise these chemicals to protect themselves from viruses, fungi, and parasites (although I have a suspicion that the slugs that regularly wipe out my kale do not read scientific papers). They indeed bind to certain micronutrients in food, thus reducing their absorbability. However, the studies also show that these chemicals, being a part of the protective system in plants, are also likely to protect our cells from damage, thus reducing the risk of cancers and heart disease (2,3). Therefore, if we look away from some scaremongering publications and more into scientific evidence, we will find that a better name for these nutrients would be ‘pro-nutrients’ and not antinutrients).

Let us have a closer look.

Phytates
Phytates (or ‘phytic acid’) are present in most plants, but the highest concentrations are in whole grains, legumes, nuts, and seeds. Phytates bind to calcium, iron, and zinc, forming large molecules that are difficult to absorb into the bloodstream and, therefore, become excreted. But nothing to worry about! Most of the food preparation methods – soaking, leavening, fermenting, sprouting, and even boiling, toasting, or otherwise cooking, break down most of the phytates and ‘free’ those vital minerals. And that is not all – breaking down phytates also makes proteins in plants easier to digest (4).

Lectins
Like phytates, lectins are found in many plants. And like phytates, lectins bind to calcium, iron, and zinc, thus interfering with their absorption. Some types of lectins found in beans, such as phytohaemagglutinin in red kidney beans, could also cause digestive discomfort or even food poisoning if the beans are undercooked. However, pre-soaking and cooking them for 45 minutes on high heat or using a pressure cooker for the same amount of time for unsoaked beans breaks down these lectins leaving all the tasty goodness and healthfulness (5).
(Anyway, raw beans, anyone? No, I thought not.)

Other types of lectins in vegetables are not toxic, and they are also broken down by the same food preparations ways as phytates.

Oxalates
Oxalates (or ‘oxalic acid’) are another type of ubiquitous compound in plants, but the highest oxalate concentration is found in leafy vegetables from the beetroot family, such as Swiss chard, rainbow chard, and beet greens, as well as spinach and rhubarb. Oxalates bind to calcium, thus interfering with its absorption. Oxalates dissolve in water, and therefore cooking methods involving water, such as boiling or steaming, are helpful.

Another suggestion would be to rely on low-oxalate calcium sources, such as kale, collard greens, and other vegetables from the cabbage (Brassica or Mustard family), as well as legumes, nuts, and seeds (see above about phytates!)). It is worth mentioning that these foods are a suitable option for people who are at a higher risk of kidney stones and need to limit or avoid oxalate-rich foods.

Glucosinolates
Glucosinolates are sulphur-containing molecules found in the Brassica family (see above) vegetables. Studies suggest that these compounds could interfere with iodine absorption and, consequently, affect thyroid hormone production, especially in predisposed individuals. However, a) this effect has only been noticed in those with suboptimal iodine intake; b) those eating a vegan diet should be careful in any case to ensure that they are getting adequate iodine either from some types of seaweed, or fortified foods, or supplements, if necessary.

What is more important to mention when talking about glucosinolates is that when we cook Brassicas, they are converted into sulforaphane and indole-3-carbinol. There is ever-growing evidence that sulforaphane and indole-3-carbinol could play a significant role in the prevention of cancer, heart disease, and several other conditions. (2).

Tannins
Tannins are a type of polyphenols (potent antioxidants found exclusively in plants) in tea, both black and green, and coffee (it is tannins that give tea and coffee their dark colour). They bind to the iron molecule, thus forming a larger molecule, which is not soluble either in water or fat. Because of this, our body cannot absorb it.

As with other ‘anti-nutrients’, there is a solution, and a very simple one – drink your tea and coffee away from meals, at least an hour before a meal, and no less than an hour after a meal. It will prevent tannins from binding to iron, and your iron absorption from food will not be affected, especially if you combine iron-rich foods with vitamin C-rich foods. Plus, you will get many health benefits from tea and coffee.

These are the most common types of ‘anti-nutrients’. There are quite a few more, such as isoflavones in soy, saponins in oats, and many others but, like the ones we discussed, they can be neutralised using the food preparation methods discussed above, or they pose no health risks in the context of a well-balanced diet. Quite the opposite, they have health-promoting qualities.

To conclude: love your plants with all your heart – and stomach! Eat as great a variety as you can – different types, textures, and colours. Enjoy some raw vegetables for a maximum of vitamins C, B6, folate, and polyphenols. Cook, sprout, ferment or leaven the others for calcium, iron, zinc, and carotenoids. Plants are full of nutrients, macro-, micro-and… pro-nutrients!

References:

1. Dr Steven Gundry. The Plant Paradox. 1st ed. HarperWave; 2017. 416 p.
2. Petroski W, Minich DM. Is There Such a Thing as “Anti-Nutrients”? A Narrative Review of Perceived Problematic Plant Compounds. Nutr 2020, Vol 12, Page 2929. 2020 Sep 24;12(10):2929.
3. Donato M, Faggin E, Cinetto F, Felice C, Lupo MG, Ferri N, et al. The Emerging Role of Nutraceuticals in Cardiovascular Calcification: Evidence from Preclinical and Clinical Studies. Nutrients. 2021 Jul 28;13(8):2603.
4. Haileslassie HA, Henry CJ, Tyler RT. Impact of household food processing strategies on antinutrient (phytate, tannin and polyphenol) contents of chickpeas ( Cicer arietinum L.) and beans ( Phaseolus vulgaris L.): a review. Int J Food Sci Technol. 2016 Sep 1;51(9):1947–57.
5. Shimelis EA, Rakshit SK. Effect of processing on antinutrients and in vitro protein digestibility of kidney bean (Phaseolus vulgaris L.) varieties grown in East Africa. Food Chem. 2007 Jan 1;103(1):161–72.