When Is a Nutrient an Antinutrient?
If you're interested in optimizing your diet, you've likely encountered the word antinutrients before. Certain experts have raised concerns about antinutrients, components of food or dietary nutrients that interfere with the absorption of other nutrients. Different antinutrients, such as phytates, oxalates, and glucosinolates can be found in various types of food, including fruits, veggies, legumes, dairy, and meat.
At this time, the long-term impact of antinutrients on human health has yet to be fully sussed out. Research has shown that while antinutrients can cause health problems, they can also bring health benefits. The majority opinion among health authorities at this time is that the advantages of eating foods containing antinutrients outweigh the adverse effects of forgoing those foods altogether.
Read on to learn more about antinutrients and how they affect your health so you can separate fact from fiction as you continue seeing news coverage on this hot topic.
What Are Antinutrients?
The answer to the question of what antinutrients are can be found in the name itself: while the term nutrients describes substances that provide the raw materials plants and animals (humans included) need to thrive, antinutrients prevent them from absorbing and utilizing those substances. In short, they block the absorption of nutrients. Antinutrients occur naturally in a variety of both plant-based and animal-based foods.
The purpose of those found in plants, like lectins, is to prevent bacterial infections and protect against consumption by predators, as an article published in Plant Physiology outlines. To illustrate that idea, consider the case of the nightshade family of vegetables, which includes potatoes, tomatoes, peppers, and eggplants. All nightshade vegetables contain solanine and chaconine, antinutrients intended to deter animals and humans alike from consuming them as they can make you sick when ingested in large doses.
A common health concern raised by those worried about antinutrient consumption is that ingesting high amounts can result in nutrient deficiencies, particularly for individuals adhering to diets that classify certain foods as off-limits, particularly vegan or vegetarian diets organized around legumes and grains. Another worry is that they may increase intestinal permeability, resulting in a health condition referred to as leaky gut.
Fact-Checking Concerns About 7 Antinutrients
As described above, antinutrients impede the body's ability to absorb essential nutrients such as vitamins, minerals, amino acids, and so on. While this clearly has the potential to be problematic, the evidence so far indicates that it's unlikely to cause issues in the absence of overall malnutrition or dietary imbalances. Furthermore, studies show that in certain circumstances, antinutrients can actually enhance a person's health—for instance, tannins found in tea can decrease cancer risk and phytic acid can lower cholesterol and triglyceride levels.
In the sections below, we'll delve into the details of common concerns raised about seven of the most significant antinutrient groups:
- Tannins and other flavonoids
- Enzyme inhibitors
Lectins can be found in all plants but in particularly high concentrations in seeds, legumes (most notably kidney beans), and whole grains as they tend to cluster in the parts of seeds that go on to become leaves after sprouting occurs.
In the popular consciousness, lectins have entered into the same category as gluten: a poorly understood substance widely believed to be, somehow, bad.
Going "lectin-free," in the way you might go gluten-free, is posited as a way to prevent leaky gut syndrome. The theory is that when you eat foods that contain high amounts of lectin, the lectin proteins bind to cells in the walls of the digestive tract where they then create minute punctures that allow the contents of the gut to leak into the bloodstream. In high amounts, lectins may also prevent the proper absorption of certain nutrients, including calcium, iron, phosphorus, and zinc.
According to a literature review published in the American Journal of Clinical Nutrition, some lectins do have "deleterious nutritional effects." The review also notes that dietary exposure to lectins appears to be widespread. However, the authors could not decisively determine whether lectins caused noticeable health issues.
A separate article states that due to the "ubiquitous" presence of lectins in plants, we all ingest them daily in "appreciable amounts"—unless, of course, you're taking steps to avoid them. The article goes on to explain that it is the ability of lectins to remain intact in the digestive tract that allows them to cause damage to its lining, though the effects it notes do not include the development of leaky gut, but rather:
- Loss of gut epithelial cells
- Damage to the membranes of the epithelium
- Impaired digestion and absorption of nutrients
- Disruption to balance of bacterial flora and immune state of the gut
Before you begin to panic about the logistical challenges of avoiding lectins, remember that researchers have yet to find conclusive evidence that consuming lectin-containing foods produces damage significant enough to impact the well-being of individuals who are otherwise in good health.
Also called phytic acid, these antinutrients can be found in many of the same foods as lectins—think legumes such as lentils, nuts, seeds, whole grains, and pseudocereals like quinoa. Their purpose for the foods that contain them is to provide the phosphorous necessary for the growing plant.
Studies show that phytates interfere with the absorption of certain minerals and trace elements, including calcium, iron, magnesium, and zinc, by binding to those micronutrients during digestion.
However, an article published in Molecular Nutrition & Food Research notes that dietary phytates also have beneficial effects such as decreasing the likelihood of kidney stone formation and keeping blood sugar and blood lipid levels in the healthy range. The authors note, too, that phytates appear to have antioxidant and possibly anticancerogenic properties.
So, it seems that the phytate content of a food should certainly not be a cause for concern and may even be a boon to your health.
Oxalates, or oxalic acid, can be commonly found in nuts and seeds as well as in leafy greens, fruits, vegetables (particularly rhubarb), and cocoa. Oxalates bind to minerals to form calcium oxalate or iron oxalate. This makes it much more challenging for the body to absorb those minerals.
A review published in the American Journal of Clinical Nutrition compared the absorbability of calcium from spinach, which contains oxalates, to that of calcium from milk, which does not, and found that the absorption from milk was always higher. The mean absorption for milk was 27.6% while spinach achieved a mere 5.1%.
In some instances, oxalates have also been linked to an elevated risk of kidney stone formation, though thanks to the high nutritional value of oxalate-containing foods, physicians no longer universally recommend low-oxalate diets to those with kidney stones. In other words, there's no need to try to avoid oxalate-rich foods due to this possible side effect. Most people will harm their health more by avoiding these healthful foods than by ingesting the oxalates they contain.
4. Tannins and Other Flavonoids
You may be confused to see flavonoids on this list, as this group of naturally occurring polyphenols (which include tannins) have often been discussed as nutraceuticals because of their antioxidant properties. However, these compounds, like the other antinutrients, chelate or bind with minerals such as iron and zinc and reduce the absorption of these nutrients.
For instance, the tannins found in tea, coffee, fruit skins, and legumes have been linked to decreases in iron absorption. Yet they have also been shown to have anticarcinogenic activity and to inhibit the growth of fungi, bacteria, and viruses.
One way to think about tannins, as an article published in Trends in Food Science and Technology aptly put it, is as "a double-edged sword." It appears, however, that consuming small quantities of tannins will allow you to access their benefits, while larger amounts are needed before the threshold for adverse effects is crossed.
These antinutrients are found in high amounts in cruciferous vegetables like broccoli, Brussels sprouts, and cabbage. Like tannins and the rest of the flavonoid family, you may be more familiar with glucosinolates as a desirable phytonutrient.
Yet the same compounds renowned for their ability to help prevent cancer also impede iodine absorption, which can lead to an iodine deficiency and impaired thyroid function. Individuals whose diets contain insufficient amounts of iodine or who have hypothyroidism (underactive thyroid) are most at risk for this issue.
There's also some indication of an association between a greater intake of glucosinolates and a higher risk of type 2 diabetes. Studies so far, such as this one from 2018, have all been population-based, making it too early to say whether there's a causal relationship at work.
6. Enzyme Inhibitors
This category of antinutrients includes protease, amylase, and lipase inhibitors, all of which impact the body's ability to digest and absorb macronutrients. They can be found in a wide swathe of the plant kingdom, including legumes, seeds, and whole grains.
A protease is an enzyme (the -ase ending in chemistry denotes an enzyme) that helps break down proteins, amylase is an enzyme that breaks down certain carbohydrates, and lipase is an enzyme that breaks down lipids (fats). If the enzyme is “inhibited,” it is prevented from breaking down the macronutrient and making it available for absorption. Therefore, protease inhibitors make the body less able to digest protein, amylase inhibitors do the same for carbohydrates, and lipase inhibitors do so for fat.
Food sources of protease inhibitors include beans and other legumes, cucumbers, radishes, broccoli, spinach, potatoes, and egg whites, which contain a trypsin inhibitor along with avidin, which interferes with biotin absorption.
Interestingly, both amylase and amylase inhibitors are touted as having health benefits. Natural dietary sources of amylase include raw fruits and vegetables, along with sprouted seeds, nuts, legumes and whole grains. Amylase inhibitors are found in Garcinia cambogia, guar, inulin, Rosmarinic acid, and other plant foods.
Lipase inhibitors, as already noted, interfere with the enzymes we use to process fats. Lipase inhibitors do not discriminate between fats, meaning absorption of good fats like omega-3 can be compromised. However, they can also be beneficial in that they protect the body from absorbing harmful fats. For that reason, the FDA approved a prescription lipase inhibitor called Orlistat that can increase weight-loss results by allowing fats to pass through your system unprocessed. Orlistat can also beneficially lower total cholesterol and low-density lipoprotein, return blood pressure levels to the healthy range, and regulate fasting glucose and insulin concentrations.
Saponins are perhaps best known for their ability to produce soapy foam when shaken with water. They can be found in a range of legumes and whole grains and can interfere with normal nutrient absorption. Per an article published in the International Journal of Nutrition and Food Sciences, they may also inhibit the actions of various digestive enzymes in the same manner as the substances discussed in the preceding section, thereby decreasing protein digestibility.
However, that same article notes that there's evidence saponins lower cholesterol. An article published in the Journal of Medicinal Food went even further, describing saponins as "health-promoting components" and praising them for their ability to decrease your risk of cancer.
Other Antinutrients You May Encounter
In addition to the seven antinutrients discussed above, you may see references to other antinutrients. Keep in mind that what findings exist about their impact on human health likely show the same complicated and contradictory results. With that said, here are several other antinutrients as well as some food sources for each:
- Allicin and mustard oil: Alliums like chives, leeks, onions, scallions, shallots, and garlic
- Alpha-amylase inhibitors: Whole grains, legumes, the skins of various nuts, and the leaves of the stevia plant
- Calcitriol, solanine, nicotine: Nightshade vegetables like eggplant, peppers, tomatoes as well as goji berries
- Goitrogens: Cruciferous vegetables, soybeans, and peanuts
- Oligosaccharides: Wheat, legumes, asparagus, and alliums
- Salicylates: Berries and other fruits like apricots as well as some herbs and spices including cayenne, ginger, and turmeric
- Uric acid: Primarily animal-based foods like meat (particularly organ meat), eggs, and dairy as well as legumes and some vegetables
How Antinutrients Affect Your Health
It's challenging to speak generally about the health effects of antinutrients since they depend on an individual's metabolism, how the food is cooked and prepared, and the presence of any food sensitivities, nutrient deficiencies, or health conditions.
Keep in mind, too, that many dietary substances can act as antinutrients under certain circumstances. For example, alcohol, when consumed in excess, interferes with the bioavailability of zinc and the B vitamins.
Also, the antinutrient only impairs the absorption of nutrients that are co-ingested in the meal. For example, a phytate-rich snack of raw almonds won’t affect the absorption of iron from a steak consumed later in the day.
There are many other strategies to “neutralize” the antinutrients found in foods. Many culinary techniques such as soaking, fermenting, and sprouting (and, of course, cooking) of beans and seeds are common approaches that increase the palatability and nutrient availability.
In a balanced, omnivorous diet, antinutrients present no problem, and the benefits they confer, such as antioxidant properties and removal of toxic metals, far outweigh any impact on mineral balance.
Vegetarian or vegan diets, on the other hand, may involve the combination of low intake of iron, zinc, and calcium and a high consumption of grains that contain phytates and other antinutrients. The result of this combination can be dietary deficiencies in minerals that, over time, lead to a deficiency. These mineral imbalances result in impaired immune function, anemia, and poor bone health, among other symptoms.
That said, there's some indication, like this study done in 2012, that the bodies of individuals adhering to such diets may adapt over time to the continued presence of antinutrients by becoming more efficient at metabolizing minerals such as iron and zinc.
Individuals with an elevated risk of developing conditions linked to mineral deficiencies, such as osteoporosis or anemia with iron deficiency may wish to consult a dietitian or nutritionist to develop an eating approach designed to improve mineral absorption. Such a strategy might be to reduce antinutrients, but that's certainly not the only method. You might instead strategically time intake of foods with high antinutrient content, such as tea, to avoid impeding mineral absorption, or plan to take a high-quality calcium supplement after consuming a legume dish high in phytates.
It's also worth noting that antinutrients can largely be minimized by food processing and by genetic engineering. In countries with less industrialized agricultural systems, antinutrients have presented nutritional problems, but in the United States, most diets contain micronutrients in amounts well above the minimal requirement.
Interestingly, the tendency to put more and more focus on the benefits of unprocessed fruit, vegetables and grains, increases the likelihood that antinutrients could undermine a well-intended dietary plan.
As established in the last section, antinutrients often have health benefits of their own. While it's true that phytates interfere with calcium absorption, they also manage the body's rate of digestion, forestalling blood sugar spikes. Because antinutrients can be quite good for you, most experts do not recommend that you avoid consuming them entirely. As long as you eat foods with a high antinutrient content in the context of a nutritious, varied diet, there's very little risk involved.
So, should you worry about antinutrients? The simple answer is that they don’t need to be a problem if care is taken in preparing foods and timing the ingestion of raw foods and snacks apart from mineral-dense meals or dietary supplements like essential amino acids. Certain foods will likely contain some antinutrients no matter how you process and prepare them, however, the nutrients found in those foods will typically have a more pronounced effect than the antinutrients. By eating a wide assortment of foods each day, and taking care not to eat meals centered on a large portion of a food source of antinutrients, you should be able to offset any potential adverse effects of antinutrients.