Lately, some people have reported making a variety of counterintuitive diet changes, such as replacing nutritional powerhouses like spinach with plain lettuce or switching from brown rice to white. Why? They read online that certain “supposedly healthy” foods actually contain “anti-nutrients,” and they’re worried that eating them will actually compromise their health.
Time, then, to clear up some confusion.
“Anti-nutrients” is a term more likely employed by people pushing fad diet books than by nutrition scientists in reference to a variety of naturally occurring chemical compounds in plant-based foods, from lectins in beans and phytate in seeds and whole grains to oxalatein spinach.
What many of these compounds – and others similarly demonized as anti-nutrients, from tannins in black tea to glucosinolates in broccoli – have in common is that they bind to certain nutrients in food or in the gut, making them more difficult for our bodies to absorb. Or, they render certain nutrients less “bioavailable” than those from other foods. For example, our bodies absorb about 30% of the calcium from milk, but only about 5% of the calcium present in spinach; this is because oxalic acid (oxalate) in spinach binds to its calcium, making the latter harder to absorb. Similarly, you can absorb a far greater percentage of the zinc in meat than you can from whole grains, nuts or seeds, because the latter contain phytic acid (phytate) that ties it up.
But the term “anti-nutrients” gives the impression that you’d be worse off by eating a food that contains these compounds, or that something in these foods actively destroys or depletes nutrient stores in your body. This is not the case. Consuming foods high in, say, oxalate or phytate doesn’t diminish your nutritional status or pull nutrients out of your body; you can and do still absorb some of these essential minerals from the plant food, just not as much as you might expect based on their total content.
Phytic acid is a plant’s storage form of the essential mineral phosphorous, and oxalic acid is a naturally occurring organic compound also found in plants. They both affect absorption of iron, zinc and/or calcium in particular. This makes them far more of a consideration for people who follow vegetarian or vegan diets – and for traditional societies consuming subsistence diets based on a small handful of staple foods. There certainly are some workarounds, however.
Consuming animal protein, including eggs and cheese, alongside phytate-rich whole grains, nuts or seeds enhances zinc absorption from the plant-based source; this is a strategy that ovo-lacto vegetarians can use. Sprouting or fermenting whole grains and beans is another way to reduce phytate content and make these minerals more absorbable for those who rely solely on plant-based foods for these essential minerals. Fermented (sourdough) or sprouted-grain breads are increasingly available in health-oriented supermarkets, as are sprouted dry beans and brown rice. Phytate’s effect on plant-based iron absorption varies by source. The iron in pea protein appears to be much more bioavailable than the iron in soy protein. Consuming vitamin C-containing foods or supplements will also increase iron absorption, including iron from plant-based sources.
Oxalic acid, found in foods like spinach, rhubarb, potatoes, wheat bran, beets, tea and berries, binds to calcium in the food itself and to calcium from other foods co-ingested with them. The resulting compound – calcium oxalate – cannot be absorbed by the intestine, and this is why so little of the seemingly high calcium content in foods like spinach is actually absorbed. If you follow a plant-based diet and don’t consume dairy, you’ll absorb more plant-based calcium from cultured soy foods like calcium-set tofu and cabbage-family veggies (kale, collards, broccoli, bok choy and Chinese mustard greens) than you will from oxalate-rich spinach and sesame seeds/tahini. However, people prone to calcium-oxalate kidney stones can hack this biochemistry to their advantage. Eating calcium-rich dairy foods – or even taking a calcium supplement – alongside high oxalate foods will create calcium-oxalate bonds in the digestive tract that prevent the oxalate from being absorbed into the body. This seems to reduce the likelihood of it winding up as fodder for kidney stones.
A family of proteins called lectins are a different story, as their impact on human health is far more theoretical and unrelated to mineral absorption. The only reason you’ve probably heard of them is because of a 2017 fad diet book that I shall refrain from naming so as not to lend it more airtime than its shoddy science deserves. The accusation lobbed against lectins in certain circles is that they could bind to the inner lining of the digestive tract, impeding absorption of other nutrients, causing inflammation and raising a purportedly toxic form of gastrointestinal hell responsible for all that ails modern humans. To say that substantiating evidence is lacking from free-living humans consuming these foods in typical quantities would be an understatement.
Missing from the fear-driven conversation about compounds labeled “anti-nutrients” is that some of them actually seem to have health benefits. Tannins in tea and red wine are credited with these foods’ apparent cancer-prevention benefits; similarly, lectins from mushrooms and other plants are being studied for their therapeutic anti-tumor/anti-cancer benefits. Moreover, whole, plant-based foods that contain lectins, phytate, oxalate and tannins have many other compounds in them as well – fiber, antioxidants and essential vitamins – that exert powerful anti-inflammatory benefits.
This latter point probably accounts for the fact that huge, long-term population-based studies show time and time again that people who consume diets highest in the foods that contain demonized “anti-nutrient” compounds – especially whole grains, nuts, orange vegetables, seeds, dark leafy greens (including spinach), berries, beans and legumes – live longer, healthier lives than people whose diets are lacking in them. They maintain healthier body weights, have lower rates of many types of cancer and are less likely to suffer from cardiovascular disease or Type 2 diabetes.
So if this is the effect of consuming a diet high in “anti-nutrients,” then sign me up … and please pass the beans. What’s that: You’re avoiding lectins? Well, then – more for me!