Published 25th July 2022

Antinutrients: A double-edged sword?

Although we like eating plants, plants don’t always want to be eaten. In response to millions of years of being chewed and swallowed, some plants have developed chemical weapons.

Today, we call some of these weapons antinutrients.

We know that eating a diet rich in plants is linked to a reduced risk of various diseases. However, some compounds in plant-based foods have developed a bad reputation.

The word “antinutrients” sounds sinister, but they’re common in many plants, including the ones you eat. 

Interestingly, some research suggests that some of these compounds might even benefit health.

Here, we’ll give you a quick overview of antinutrients and how they work. We’ll also look at how scientists are finding innovative uses for these mysterious-sounding compounds.

What are antinutrients?

In short, antinutrients are compounds that interfere with your body’s ability to use the nutrients you consume. 

They can be drugs, proteins, or chemicals in food. And, in a fascinating plot twist, even some nutrients can act as antinutrients — more on that later.

Although antinutrients can interfere with how your body absorbs and uses nutrients, you destroy many of them through cooking. 

Other times, the compounds are present in such small quantities that they're unlikely to harm your health when eaten as part of the whole food — compared with eating them as a single compound.

So, let’s get into it.

Examples of antinutrients

The best way to understand how antinutrients work is to look at some examples:

Glucosinolates 

Glucosinolates naturally occur in cruciferous vegetables, including broccoli, Brussels sprouts, cabbage, and cauliflower. They’re also present in sweet potatoes, soybeans, and more.

Glucosinolates reduce your thyroid’s ability to make hormones. If consumed in excess, this can cause the thyroid gland to become enlarged, leading to a condition called goiter.

However, this is most likely in people who already have an iodine deficiency, which is very rare in industrialized countries.

Thankfully, we can still enjoy these delicious greens because both freezing and cooking significantly reduce the levels of these compounds. 

In fact, boiling them for 5 minutes halves the amount of glucosinolates in a vegetable. And microwaving them reduces levels by 17.3%–27.4%. 

As we’ll see later on, the relationship between glucosinolates and health isn’t quite as one-sided as it seems.

Oxalates

Oxalates and oxalic acid occur in many types of plants, but they are particularly abundant in tea, spinach, parsley, and rhubarb (especially the leaves). 

These compounds bind to calcium and other minerals, stopping them from dissolving. Once bound, the body can’t absorb them.

Scientists have calculated that 0.77 ounces (22 grams) of oxalic acid would kill a human, which doesn’t sound like much. 

However, in real terms, that would mean eating almost 10 pounds (4.5 kilograms) of rhubarb leaves, which would be quite a feat of endurance.

Although there are documented cases of rhubarb poisoning, experts think that, in these cases, oxalates might not have been the culprit but rather some other compound in rhubarb.

Like glucosinolates, some oxalates break down during cooking. And, unless you're consuming a great deal of these foods, there’s nothing to worry about anyway. 

Enzyme inhibitors

Glucosinolates and oxalates act as antinutrients because they stop your body from absorbing nutrients. Other antinutrients work differently.

For instance, soybeans, kidney beans, and some other grain legumes contain compounds that block an enzyme called trypsin.

Trypsin is an important digestive enzyme that breaks down proteins.

In animal studies, these trypsin inhibitors can reduce protein and amino acid uptake by 50%. Luckily for us humans, cooking removes the majority of these enzyme-blockers.

Calcium, the double agent

As a final example, we’ll look at the strange case of a nutrient acting as an antinutrient. 

If you eat foods rich in calcium — an essential nutrient — with foods containing iron — another essential nutrient — the calcium becomes an antinutrient: It partially blocks iron absorption.

Scientists don’t know exactly how this happens, but they think calcium interferes with how iron is transported from the gut into the body. 

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This could be a concern because experts often recommend for women and children to take on more calcium. And women and children are also most at risk of iron deficiency.

But studies have found no links between high calcium intake and iron deficiency.

So, before you throw out your milk, it seems that the antinutrient effects of calcium are short-lived or your body has another mechanism that deals with this problem.

Could antinutrients benefit health?

Although antinutrients could potentially impact health, some scientists are looking at ways to use these compounds to improve health. Let’s look at a couple of examples.

Lectins

Lectins are found in some nuts, cereals, and legumes, such as lentils. Cooking foods that contain lectins makes them safe to eat. 

However, if you eat them in large amounts without cooking, they can interfere with digestion and absorption of nutrients.

Some scientists are now investigating whether lectins might help treat cancer. 

For instance, a group of researchers showed that a plant lectin called Abrus agglutinin might help slow the spread of oral cancer. Another team investigating the same lectin found that it might help slow the progression of colon cancer.

To be clear, though, scientists conducted these studies in the laboratory rather than on humans — eating fistfuls of raw lentils will not reduce cancer risk, and it will make you sick. 

Glucosinolates again

We met these compounds earlier — they can interfere with hormone production in the thyroid. And they are commonly found in cruciferous vegetables, like Brussels sprouts and cabbage.

However, they may be a double-edged sword. As an example, some research hints that cruciferous vegetables might help protect against thyroid cancer, although not all studies agree.

Other scientists have investigated the effects of a high-glucosinolate broccoli soup on people with prostate cancer.

Their results hint that increased glucosinolate intake might slow progression of the disease. It's important to note, though, that larger, longer studies are needed to confirm the benefits.

Beyond cancer, a review of glucosinolates mentions a range of potential health benefits, including reduced inflammation and protection against infections. 

It’s important to note that much of the evidence for these benefits comes from laboratory studies and animal models rather than human trials. There’s a lot more exciting science to be done before we get to the bottom of glucosinolates.

Oxalates revisited

Oxalates are the rhubarb compounds that bind minerals, like calcium. Until recently, scientists believed oxalate intake might be related to kidney stone formation.

This was partly because an estimated 65% of kidney stones consist of calcium oxalate.

However, more recent studies suggest that although a higher intake of oxalate is linked to kidney stones, this relationship was strongest in those who aren’t consuming enough calcium. 

So, rather than cutting down oxalates to prevent kidney stones, taking in enough calcium might be your best bet.

It’s also worth saying that a plant-heavy diet — including plants containing oxalates — reduces your risk of kidney stones.

What should you do?

We’ve seen that many plants we enjoy eating contain antinutrients. We’ve also seen that, although their powers seem concerning, if we prep our food in the normal manner, they are mostly extinguished.

We’ve also seen that some of these antinutrients might have health benefits and that scientists are investigating some to create new drugs and treatments.

At ZOE, we know that a diet including plenty of fresh fruit, veg, and whole foods is the key to health.

It’s less about individual compounds within any given food and more about how those compounds interact with the whole food and with your body.

With our at-home test, you can learn more about how your body uniquely responds to food.

Sources

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Antinutritional properties of plant lectins. Toxicon. (2004). https://www.sciencedirect.com/science/article/abs/pii/S0041010104001916 

BMI, diet and female reproductive factors as risks for thyroid cancer: a systematic review. PLOS ONE. (2012). https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0029177  

Calcium and iron absorption--mechanisms and public health relevance. International Journal for Vitamin and Nutrition Research. (2010). https://pubmed.ncbi.nlm.nih.gov/21462112/ 

Dietary Factors and the Risk of Incident Kidney Stones in Younger Women Nurses' Health Study II. JAMA Internal Medicine. (2004). https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/216978 

Dietary habits and thyroid cancer risk: A hospital-based case–control study in Sicily (South Italy). Food and Chemical Toxicology. (2020). https://www.sciencedirect.com/science/article/pii/S0278691520306682  

Effect of perchlorate and thiocyanate exposure on thyroid function of pregnant women from South-West England: a cohort study. Thyroid Research. (2018). https://thyroidresearchjournal.biomedcentral.com/articles/10.1186/s13044-018-0053-x 

Effects of antinutritional factors on protein digestibility and amino acid availability in foods. Journal of AOAC INTERNATIONAL. (2005). https://academic.oup.com/jaoac/article/88/3/967/5657528 

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p73 induction by Abrus agglutinin facilitates Snail ubiquitination to inhibit epithelial to mesenchymal transition in oral cancer. Phytomedicine. (2019). https://www.sciencedirect.com/science/article/abs/pii/S094471131830268X 

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