Most health and sustainability experts agree that most people would benefit from a plant-forward diet. Fruits, vegetables, legumes, whole grains, nuts and seeds contain a wide variety of beneficial nutrients for us and our gut microbiota. Plants produce molecules called polyphenols, which often serve as defenses for plants and have antioxidant and other favorable properties for the humans who consume them. And yet, proponents of fad diets like the Paleo and ketogenic diets have blamed the components of plants known as antinutrients for many of the inflammatory diseases that people experience. Should we be concerned about antinutrients in our diets?
What are antinutrients?
Antinutrients are compounds found in plant foods that inhibit the body's ability to absorb certain nutrients after digestion. The mechanisms typically fall into two categories: binders of micronutrients or inhibitors of digestive enzymes.
Plants produce antinutrients to protect themselves from predators, which wisely learn to avoid consuming plants high in these compounds after suffering from their effects. When humans eat macromolecules (carbohydrates, fats and proteins) that contain these antinutrients, these foods can often pass through the gastrointestinal tract undigested. Unfortunately, fundamental nutritional deficiencies and/or inflammation can result. Antinutrients are particularly abundant in grains and legumes, often considered staples in healthy diets; these foods are also excellent sources of fiber for our microbiota. See the table below for a list of common antinutrients.
As examples:
Antinutrients called phytates have a high affinity for the minerals listed in the table above, which may cause them to bind, thus preventing the absorption of those minerals in the GI tract. Unfortunately, the human body doesn’t make the enzyme (phytase) that breaks down phytates, meaning we can't easily inhibit their action.
Oxalates chelate (or bind to) calcium and prevent it from being absorbed. In sensitive individuals, high-oxalate diets can cause calcium crystals to form that may stick together and result in a solid mass (a kidney stone).
Lectins have also received increased negative attention. They are proteins found primarily in legumes and nightshade vegetables (i.e., members of the Solanaceae family such as tomatoes and eggplant) used for cell signaling or as protective mechanisms; they can also be found in animal foods, though these lectins are typically not problematic. In our bodies, lectins bind to cells lining the small intestine and cause atrophy and malabsorption. The good news is that many food processing methods deactivate lectins. Therefore, only the consumption of raw legumes and grains (which is uncommon) would be a cause for concern.
Not all antinutrients are problematic, and they may also have positive effects. For example, tannins are polyphenols, which act as antioxidants in humans and contribute to the health properties of teas, wine and more. Similarly, other antinutrients may be metabolized by our gut bacteria to produce beneficial compounds.
How does consuming antinutrients impact my health?
Although their effects on digestion and absorption are acknowledged, we don't yet have clinical evidence to show that eliminating these molecules from the diet can cure diseases like autoimmune diseases. Indeed, the Mayo Clinic doesn't recommend avoiding antinutrients in the diet but instead advises monitoring symptoms and experimenting with elimination diets when necessary. In addition, preparing these foods appropriately (see below) can potentially mitigate the adverse effects of these foods on the immune system and gastrointestinal tract. Therefore, broad recommendations to avoid foods that contain them are typically unfounded.
How do humans reduce antinutrient content in foods?
To prevent the negative effects of antinutrients, cooks around the world have discovered over time that soaking, sprouting, fermenting and wet heating food all help to inactivate the antinutrients in plant foods:
Soaking plant foods for an extended period and then disposing of the soaking water reduces antinutrients because many antinutrients are water-soluble.
Sprouting helps to degrade antinutrients such as phytates and protease inhibitors.
Fermenting involves the use of bacteria to oxidize carbohydrates, creating an acidic environment that can deactivate antinutrients.
Heating foods through various methods can degrade antinutrients.
Further, foods can undergo multiple forms of processing, which can have a cumulative effect on antinutrient composition (as evidenced in the chart below).
Studies suggest these methods work to varying degrees, and they differ by food group. For example, soaking and cooking have been shown to reduce levels of lectin and oxalate but not necessarily of phytic acid. Also, soaking and then cooking better reduces antinutrient levels than either method alone. The figure above shows the cumulative effects of various types of processing on the phytic acid content in soy. These processes can also improve nutritional quality. Sprouting, for example, breaks down some of the starch, helping to lower the glucose response after consumption. Also, fermented foods (that are not pasteurized) contain live probiotics that help feed our gut microbiota.
A recent study suggested that among legumes, soybeans contain the most antinutrients. Traditionally, soy was properly processed to remove these antinutrients before consumption. However, the isolated forms of soy protein found in many industrially processed foods in the standard American diet have not been processed using traditional methods (see figure below for examples). And because shelf-stable convenience foods have become increasingly prevalent in our food supply, the standard American diet doesn't contain many other plant foods that have been prepared in ways that inhibit or remove antinutrients.
Thankfully, more people are buying foods that have been properly processed (i.e., with antinutrients removed) and learning how to do it themselves. They are driven by their concern about the connection between diet and inflammation, irritable bowel syndrome (IBS) and even the links between gut health and distant organ systems. This is helping to grow the market for more nourishing foods processed using traditional methods.
Milling grains can also reduce their phytonutrient content, but this process of refining also removes many of their beneficial nutrients. Biotechnology is also using methods to change plant genetics to reduce the creation of these molecules in agricultural production or to fortify the micronutrients to maximize bioavailability. This is particularly appropriate in developing countries where people suffer more from micronutrient deficiencies.
How should I manage antinutrients in my diet?
Foods should not necessarily be avoided just because of their antinutrient content. They may have many other beneficial properties, such as omega-3 fatty acids, protein or fiber. Also, everybody's body responds differently, so antinutrients may not be a concern for many individuals.
Soaking, sprouting, fermenting and some methods of heating food help to inactivate the antinutrients in plant foods. Choose these forms (especially for soy) at the grocery store, when possible, and try these methods when cooking foods that contain antinutrients at home.
Talk to your doctor or a registered dietitian if you notice symptoms like diarrhea, flatulence, fatigue, etc., that you think may be attributed to your diet. They may work with you on an elimination diet to determine the culprit food group and how to remove it without risking deficiencies.
These molecules may be particularly problematic if you have an inflammatory disease, such as Crohn’s disease, colon cancer or rheumatoid arthritis. You should seek assistance from a dietitian in identifying sources of antinutrients in your diet and the best ways to remove them.
Resources
A full list of resources can be found here.
Christina Badaracco, MPH, RD
Christina is a registered dietitian and author who aims to improve access to healthy and sustainable food and educate Americans about the connections between food and health. She loves to experiment with healthy recipes in the kitchen and share her creations to inspire others to cook.
Christina completed her dietetic internship at Massachusetts General Hospital and earned her Master of Public Health degree from the University of California, Berkeley. Previously, she graduated with a degree in Ecology and Evolutionary Biology from Princeton University, after conducting her thesis on sustainable agriculture and energy in Kenya. She has done clinical nutrition research at the National Institutes of Health, menu planning and nutrition education at the Oakland Unified School District and communications at the Environmental Protection Agency's Office of Water. She has also enjoyed contributing to children’s gardens, farmers markets and a number of organic farms.