Anti-nutrients are real, but the science suggests they're far less harmful than viral posts imply

Some context on anti-nutrients

If asked to say the first thing that comes into mind when hearing the word “nutrients”, you might think about iron, protein, magnesium, zinc or certain vitamins…,which would all be correct. What about “anti-nutrients”?

Anti-nutrient factors (or sometimes referred to as “anti-nutrients”) is a term that has been used to refer to certain natural components present mainly in legumes and cereals (among other plants) which, in some cases, can interfere with the absorption of essential nutrients (source). Common anti-nutrient factors include phytic acid (phytates), oxalates, goitrogens, lectins, tannins and saponins, which may bind to minerals such as iron, calcium, magnesium and zinc, or affect the digestibility of proteins, thereby limiting their absorption in the digestive tract. However, the impact of these compounds depends on their concentration, the food matrix, and how the food is processed;  soaking, milling, roasting, cooking, germination and fermentation all significantly reduce the anti-nutrient levels and mitigate negative effects (source; source).

Important nuance:

Some anti-nutrient factors like tannins, phytates and saponins have also been linked to antioxidant and anti-inflammatory properties, potentially protecting against oxidative stress and certain diseases. These benefits highlight the importance of not demonising specific foods, but rather ensuring that the emphasis is on healthy eating patterns, with optimal food preparations, and adequate for each person’s needs and health status (source). 

Claim 1: “Studies have shown that corn and corn products will block out 100% of zinc absorption and beans will block out 75 to 100% of zinc absorption”

Fact-check: This claim is exaggerated. Current studies show partial, not total, effects in absorption.

The claim that corn and beans block 75-100% of zinc absorption is not strongly supported by current research. While it is true that beans contain some anti-nutrient factors like phytates and lectins that can inhibit mineral absorption, the extent of this effect varies and is generally less absolute than stated.

Phytates and lectins, like other anti-nutrient factors, are heavily affected by soaking and cooking. When properly soaked and/or cooked, and eaten in moderate amounts, they present little concern for most people and are very unlikely to completely block mineral absorption, especially when included within a varied and balanced diet (source).

Who should be extra aware?

Some people, including those who have had gastrointestinal disorders, are pregnant or lactating, people who follow a vegetarian/vegan diet, or those with other relevant medical conditions, may have lower levels of zinc. In these instances, it is especially important to follow certain food preparation techniques, such as soaking and properly cooking, to reduce the binding activity of zinc by phytates (source), and seek personalised advice from a health professional, such as a registered nutritionist/dietitian, to prevent any deficiencies.

Canned beans are another healthy, affordable and convenient option. Pairing beans with some vitamin C sources, such as tomato, bell pepper or a dash of lemon may also help to increase zinc absorption, as well as eating fermented foods, such as tempeh and miso (source).

Claim 2: “Antinutrients are blocking out the nutrient absorption (and) if you’re eating antinutrients then you need an over abundance of these nutrients”

Fact-check: Misleading. The effects of anti-nutrient factors are not as absolute as presented.

Anti-nutrient factors may reduce absorption of some minerals and proteins, but they do not typically  “block out” absorption completely, especially within a varied and balanced diet.  The idea that anyone eating plants therefore “needs an overabundance” of nutrients is an oversimplification.

Several literature reviews describe a negative relationship between a high content of anti-nutrient factors and mineral bioavailability, but they emphasise processing, food preparation, and overall diet quality as the main tools to manage this, and not an “overabundance” of nutrient intake. Following a balanced, diverse eating pattern, and using a combination of preparation methods (soaking, fermenting, properly cooking), it is possible to reduce the level of anti-nutrient factors in foods and absorb higher levels of micronutrients for most people (source).

Claim 3: “Coffee will strip out magnesium”

‍Fact check: Partially true but overstated. The effect of coffee on magnesium excretion is temporary.

Though coffee and caffeine can increase the urinary losses of magnesium (and other minerals, including calcium and potassium), this excretion is usually temporary, with studies showing a peak in excretion in the first hour and then a fall within a few hours after caffeine intake, followed by a return toward baseline over the rest of the day (source).

At common intakes of coffee (1-3 cups a day) and with an adequate intake of dietary magnesium, evidence does not currently link drinking coffee in moderation with a clinically significant magnesium depletion in otherwise healthy adults with adequate dietary intake. Some magnesium sources include green leafy vegetables, legumes, nuts, and whole grains (source).

Claim 4: “Goitrogens (can cause) goiter (...) by blocking iodine uptake in your cells”

Fact check: True, but misleading. The presence of goitrogens in foods is not, per se, a reason to avoid them.

Goitrogens are natural compounds present in some foods that, when eaten in large amounts and over time,  can potentially disrupt thyroid function by inhibiting iodine uptake and may contribute to thyroid-related issues. Foods that contain these components include soy, cassava, and cruciferous vegetables (e.g., cabbage, broccoli, and cauliflower). However, studies have shown that common cooking methods, such as boiling, steaming and stir-frying, can reduce the content of goitrogens in foods (source).

Populations with existing iodine deficiencies who consume high amounts of goitrogenic foods may be at a greater risk of iodine deficiency. This also applies to people who completely avoid dairy products and fish. In this case, the main focus should be on ensuring that iodine consumption is adequate, as opposed to removing certain foods. Cooking with iodised salt is an easy way to increase iodine consumption. For people who have adequate iodine intakes and eat a variety of foods, there are also no indications to remove goitrogen-containing foods from the diet. Some common sources of iodine include dairy products, iodised table salt, white fish, and fortified products  (source; source). 

In general, for people with gastrointestinal disorders, thyroid disease or nutrient deficiencies, seeking personalised dietary guidance is advisable.

Overgeneralisation and cherry picking in social media

Presenting only evidence that supports an influencer’s point, and extending it to all people, food groups or situations, is common in health and food claims, and is an example of how popular posts often rely on:

• Overgeneralisation: The claim is based on limited or specific evidence that is extended to all people, all foods, or all situations. Saying beans or corn “block” zinc absorption for everyone is a classic overgeneralisation because the actual effect depends on phytate dose, overall diet, and food preparation. A biological mechanism is identified (anti-nutrient factors can affect mineral absorption) and then oversimplified into a cause/effect conclusion that cannot be vastly generalised.
• Cherry-picking: when someone selects only the evidence that supports their point and leaves out evidence that goes against it. In nutrition debates, this often looks like citing one study or one extreme outcome while overlooking the broader body of evidence that does not. What is also not explored is all of the health benefits of, say, coffee. So one point is highlighted (plants contain anti-nutrients) that fits with the carnivore diet promotion, but the literature on the benefits of coffee is not mentioned.

When faced with a food and nutrition claim, one can:

1. Check if cited studies are clearly identified and support the claims
2. Verify what national health/nutritional authorities recommend (WHO, NIH, EFSA)
3. Verify if the influencer has specific interests behind the claims made. For example, if they sell products or services tied to the claims.

Bottom line

The claims by Chaffee take real nutrition mechanisms, such as anti-nutrient factors and impact on mineral absorption, and turn them into absolute claims that the evidence does not support. Though research has shown that some anti-nutrient factors in plant foods can reduce nutrient bioavailability or affect digestion, particularly at high intakes, it has also shown that common food processing (such as soaking, cooking, fermenting) can lessen these effects to a great extent. 

We contacted Dr. Anthony Chaffee for clarification and asked about the studies behind the claims. We appreciate his response and the depth of the information provided. In his reply, he referred to different studies on zinc absorption from black beans and corn tortillas, caffeine and magnesium excretion, and goitrogenic compounds in plants. We reviewed the studies shared, and while they support the existence of these mechanisms in specific contexts, on their own, they do not change the final verdict of this fact-check, which also takes into account the broader evidence on nutrient bioavailability, food preparation, and overall dietary patterns. They do not show that eating or drinking a specific food will inevitably lead to deficiency, nor do they support the idea that plant-based foods should broadly be cut to prevent nutrient deficiency. Some of the studies shared also conclude that preparation and cooking methods can decrease the impact of anti-nutrient factors on mineral absorption, as presented in this fact-check. The sources he shared are available in the sources section below.

Disclaimer

This fact-check is intended to provide information based on available scientific evidence. It should not be considered as medical advice. For personalised health guidance, consult with a qualified healthcare professional.