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Anti-nutrients are biologically active plant compounds that can influence nutrient absorption, but in real-world, varied diets they rarely cause deficiencies. When foods are properly prepared and eaten as part of a balanced pattern, the benefits of plant-rich eating overwhelmingly outweigh the risks.
In this glorious golden age of nutritional clickbait, it was only a matter of time before vegetables - the food group practically synonymous with healthy eating - got their turn on the hot seat. Yes, the veggies we've been all told to eat more of for as long as we can remember now stand accused of harbouring dangerous anti-nutrients. These naturally occurring chemical tricksters are blamed for hampering mineral absorption, flaring up inflammation, and even contributing to the development of chronic diseases.
In this article, you'll learn:
To many in the carnivore and carnivore-adjacent camps, plant-defence molecules like oxalates, phytates, lectins, goitrogens, and tannins are nothing short of biological booby traps, and reason enough to avoid eating plants altogether. The logic is that since plants can't get up and run from pests and predators, they've evolved a variety of chemical weapons to defend themselves with weapons to which the human body is not at all immune.
To many others in the omnivorous or plant-based camps, anti-nutrients are not only harmless but in most cases misunderstood allies with beneficial effects depending on dose, context, and preparation.
So, what's going on? Is it true that you should start eyeing your salad with suspicion? Or, is this yet another case of online dietary paranoia getting totally out of control? As you'll see, anti-nutrients are neither to be feared and avoided, nor completely ignored - there is an important middle ground to consider. Some nuance will be required to really give this issue the treatment it's due, so let's peel back the layers and take a close look, one by one, at the anti-nutrients standing trial.
Spinach, Swiss chard, beets, almonds, and cocoa are all rich in oxalic acids. These, in turn, bind to calcium and other minerals to form oxalates. This reduces absorption of those minerals, and the oxalates continue to aggregate together, forming sharp crystals in the body. The kidneys are tasked with filtering them out into urine, and most kidney stones are largely made of calcium oxalate crystals. It's not surprising, therefore, that individuals susceptible to kidney stone formation are sometimes counselled to embrace low-oxalate diets.
However, oxalate accumulation can happen just about anywhere in the body. This truth is enough for some people to blame almost any imaginable symptom- from pain in the joints or genitals to ocular or neurological disorders- on oxalates, and to make a long-term lifestyle of avoiding them.
The issue is a confusing one because oxalate-rich foods are also some of the most nutritious on the planet (spinach being a prime example). Large population studies have found only a weak link between dietary oxalates and stone risk - and diets like the Mediterranean and DASH, both loaded with oxalate-containing foods, are protective against kidney stones and many other health conditions.
Getting enough calcium seems to be key for neutralizing the body's oxalate load- and may even be the most critical factor in avoiding kidney stones. Meanwhile, boiling veggies like spinach and chard can also reduce oxalates by up to 87 per cent.
Lectins are small proteins found in a wide range of plant foods, especially legumes and whole grains- that stick to carbohydrates. Highly bio-active and capable of binding to the surfaces of cells, some have been shown to hamper nutrient absorption, trigger inflammation, and damage the intestinal lining, especially when consumed raw or in large quantities.
Soybeans, kidney beans, and whole wheat contain some of the most well-studied lectins, such as phytohemagglutinin (PHA) and wheat germ agglutinin (WGA). Both of these resist digestion and remain problematically 'sticky' unless properly prepared. Undercooked kidney beans, in particular, have caused many well-documented food poisoning outbreaks, and it's all down to lectins.
The good news is that risk plummets with proper preparation. Pre-soaking beans, followed by boiling them for at least 10 minutes, eliminates nearly all lectin activity. In controlled trials on humans, diets rich in cooked legumes have been associated with reductions, not increases, of inflammation. Fascinatingly, emerging research is exploring the ability of lectins to selectively bind to cancer cells. The hope is that the cytotoxic properties of plant-derived lectins can soon be incorporated into viable anti-tumour treatments.
There is no question that the biological activity of lectins is very real. Nevertheless, the significance of dietary lectins in well-cooked foods remains minimal- and well worth the effort.
Unique in the world of anti-nutrients, phytates and phytic acids are not chemical defence systems, but storage forms of phosphorus. Found mainly in grains, seeds, nuts, and legumes, they're designed by plants to store energy and enable plant growth. But in the human gut, they can bind up positively charged minerals like calcium, iron, and zinc, making them more difficult to absorb.
It's true that phytates do inhibit mineral absorption, this isn't made up. However, their real-world impact on mineral status over time appears to be inconsequential. Long-term studies have shown that vegetarians and vegans, who often consume the most phytates, don't have higher rates of iron deficiency. And one controlled trial even found a 41 per cent increase in iron absorption over the course of eight weeks on a high-phytate diet, indicating that the body can adapt to phytate intake over time.
Moreover, it should be noted that phytates aren't just mineral blockers but also potent antioxidants. They regulate iron overload, protect DNA from oxidative stress, support natural killer cell function, and might even help suppress cancer development. Exciting research has further suggested that phytates may also slow arterial calcification and the accumulation of proteins associated with Alzheimer's and Parkinson's.
Up next are the 'goiter' molecules. The most well-known goitrogens are glucosinolates, naturally abundant in cruciferous veggies like kale, cabbage, broccoli, and Brussels sprouts. In the body, these glucosinolates metabolize into other compounds like goitrin and thiocyanate- both of which can potentially affect iodine uptake and thyroid hormone production.
However, whether or not eating cabbage will actually bother anyone's thyroid has almost everything to do with their iodine status. Some concerning effects have been seen in animal studies, people with preexisting thyroid disorders, or full-on iodine deficiency. But in healthy individuals, multiple human studies have found that even high intake of cruciferous vegetables has little to no impact on thyroid hormone levels whatsoever.
The more thyroid-conscious among us can take heart in knowing that boiling or steaming brassicas reduces their glucosinolate content by up to 90 per cent. Broccoli deserves special mention as it's both relatively low in progoitrin, the glucosinolate most strongly associated with negative thyroid effects, and generously endowed with glucoraphanin, a precursor to the legendary sulforaphane, which is famous for its anti-inflammatory and anticancer properties.
Please see also Brassicas: These Veggies Are Not Like the Rest
Tannins are polyphenolic compounds found in high amounts in wine, tea, coffee, and chocolate. Unlike other anti-nutrients, these are readily detectable: that dry or astringent flavour left on the palate after a sip of English Breakfast? That's the unmistakable taste of tannins on the tongue. Like the other anti-nutrients we've seen, tannins can bind to minerals, especially non-heme iron, and reduce its absorption when consumed alongside food.
If you're prone to low iron status or anemia, you might consider some clever pairings. For example, since vitamin C boosts non-heme iron availability inhibitory, the negative effects of tannins on iron absorption can be effectively counteracted with even small amounts of it. A quick squeeze of lemon on the salad can make all the difference. Additionally, spacing tannin-rich drinks like tea or red wine at least an hour before or after meals can significantly help to minimize the nutrient interference.
Crucially, the same tannins offer some amazing health benefits, bearing truly potent antioxidant, anti-inflammatory, and antimicrobial properties. Catechins and theaflavins in particular- two major classes of tannins found in black tea and green tea- have been linked to fewer cardiovascular complications, reduced LDL oxidation, and enhanced blood sugar balance. Furthermore, several population studies have shown no consistent association whatsoever between tea consumption and iron deficiency in healthy adults, suggesting that regular intake is not problematic for most people.
For a deep dive into green tea, please see Green Tea: The Emerald Elixir of Longevity.
In the final analysis, it is 100 per cent true that anti-nutrients and their effects are very real and well-documented. A basic knowledge of these fascinating chemicals in plants can add nuance to our perspective of foods and their amazing complexity. However, if our awareness of anti-nutrients threatens to veer into paranoia or any type of disordered eating, we would likely be better off forgetting the whole issue altogether.
A major lesson from anti-nutrients is that how we handle food makes all the difference: sprouting and fermenting, strategic combining, or even just soaking and cooking are great practices for every one of the potentially troublesome compounds listed above. In a way, modern science has confirmed that our ancestors knew what they were doing, and these traditional methods of food prep evolved with a lot of wisdom and understanding.
If we do have a certain health condition that invites specific awareness around a type of anti0nutrient in particular, then it makes even more sense to empower ourselves by learning about it. For example, someone with Hashimoto's might do well to consider goitrogens, and someone with a tendency toward kidney stones could very likely benefit from oxalate awareness or even a low-oxalate diet.
But even in those fairly specific situations, avoiding all plants for fear of anti-nutrients is ill-advised. The nutritional consensus, overwhelmingly, is that getting more whole plant-based foods in our diet is something almost all of us should be trying to do, and none of the conversations about anti-nutrients, in the final analysis, do anything to undermine this recommendation. Boil them or sprout them, or even have them raw… but eat them!
Q: Do anti-nutrients in plant foods cause nutrient deficiencies?
Not in balanced and varied diets. Most concerns come from isolated cases, specific health conditions, or food-insecure populations lacking in dietary diversity and nutrient intake.
Q: Are raw veggies dangerous to eat?
Only certain ones and in very large quantities. For example, raw red kidney beans are indeed toxic. But such examples are few and far between.
Q: Do I need to always soak dried beans?
You don't need to, but pre-soaking them helps reduce the effects of anti-nutrients like phytates and lectins. Whether you soak them or not, cooking them thoroughly is the most important thing.
Q: Should people with thyroid conditions avoid cruciferous vegetables?
Not according to the science. Especially if iodine intake is adequate and the veggies are cooked, most people with thyroid issues tolerate them quite well, and indeed benefit from them. Since cruciferous veggies tend to be high in FODMAPs, IBS sufferers sometimes find benefit in reducing them, but even this is generally best as a temporary strategy.
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