July 2011 Issue
Nutritional Anomaly — Might Antinutrients Offer Some Benefits?
By Sharon Palmer, RD
Vol. 13 No. 7 P. 54
You probably first heard the term “antinutrients” in a college nutrition course. You might have learned that these chemically active substances, often found in the leaves, roots, and seeds of a variety of edible plants, act in ways to combat plants’ nutrients, either by reducing their availability or otherwise adversely affecting them. Scientists identified antinutrients decades ago, discovering that some bind to nutrients, thereby preventing their digestion and utilization by the body, while other antinutrients appear to be toxic at high levels.
What’s nature’s purpose for antinutrients? Scientists suspect that they help ensure the survival and propagation of a plant species. A. Venket Rao, PhD, professor emeritus from the department of nutritional sciences at the University of Toronto, who has studied compounds found in plant foods, believes plants synthesize antinutrients as a defense mechanism against insects, parasites, and other bacterial and fungal infestations.
“For example, fruits contain seeds for the purpose of propagation of their species. However, if birds and animals were to eat the fruits containing the seeds and digest them to obtain additional nutrients and calories, then there will be no seeds left for the continuation of the plant species,” explains Rao. “So they make compounds that are so bitter that birds and animals discard them while consuming the fruits. Some of these compounds may also prevent the activity of the digestive enzymes, so that even if the seeds are consumed, they are excreted without altering their physiology.” Thus, antinutrients are part of a plant’s chemical defense system against invaders to ensure its survival.
But when it comes to antinutrients’ role in human health, recent research suggests these substances may be getting a bad rap.
Where the Antinutrients Are
Antinutrients exist in a wide range of plant foods, but they are found in particularly significant amounts in cereals and legumes, such as wheat and beans. Among the dozens of different antinutrients are enzyme inhibitors, flatus factors, saponins, and phytates. Consider phytates, which are found in grains—these antinutrients act to reduce the bioavailability of minerals and the digestibility of proteins and carbohydrates found in the grain. Rao reports that phytates can make the minerals calcium and zinc unavailable, resulting in the classical dwarf syndrome known in Egypt. In this country, people sometimes consume high levels of phytates in unleavened bread, which can lead to severe zinc deficiencies and growth impairment in children.
“The negative effect of antinutrients is mainly due to their effect on the absorption and utilization of nutrients,” says Rao. “For example, legumes contain compounds called enzyme inhibitors—in particular, an enzyme inhibitor called trypsin inhibitor, present in soybean. These enzyme inhibitors prevent digestion of dietary proteins and make then unavailable as nutrients, leading to protein deficiencies and related health disorders.”
But processing, such as the cooking, soaking, germination, and fermentation of particular plant foods, decreases the content of antinutrients such as phytates. Perhaps that’s why so many early cultures figured out they were better off soaking and cooking certain foods, such as grains and legumes, rather than eating them raw.
A New Perspective
Food scientists have known about the existence of many antinutrients, but they are just scratching the surface when it comes to understanding these substances’ overall function in human health. A new theory is beginning to emerge that suggests low levels of antinutrients may contain beneficial properties for the body. This shouldn’t come as a surprise since a body of evidence links the consumption of whole plant foods with a range of health benefits.
“There are some misconceptions with regards to what antinutrients are and their impact on human health. By definition, antinutrients are compounds, either natural or synthetic, that prevent the utilization of nutrients,” says Rao. “As a result of this concept, antinutrients were considered by nutritionists as being undesirable and compounds that needed to be removed from our foods by processing or genetics. However, recent research has shown that what we consider as antinutrients may in fact be beneficial to our health.”
Rao points to dietary fiber as a good example of how antinutrients may actually be beneficial. Long ago, there was no known nutritional role for dietary fiber. In fact, according to Rao, researchers believed that dietary fiber could bind to minerals and some other nutrients and make them unavailable. As a result, cereal-processing technology was developed in the late 1800s to remove or reduce dietary fiber from cereals and flours.
Today, we know dietary fiber serves a very important role in human health. Fiber is now considered to play a role in preventing cancer, cardiovascular diseases, diabetes, and many other chronic human diseases. “So dietary fiber, once thought to be an antinutrient, is now considered beneficial,” says Rao.
The viewpoint on antinutrients has changed to such an extent in the scientific community that Rao reports these substances are increasingly referred to as “biologically active compounds” in food.
“Our early research with dietary fiber contributed considerably to this change in thinking. Following on the dietary fiber work, we have conducted extensive research on several other so-called antinutrients, such as saponins, trypsin inhibitors, and lectins, and showed that they may play a role in the prevention of human chronic diseases, such as cancer, cardiovascular diseases, diabetes, and several other human health disorders,” says Rao. “The question seems to be one of concentrations in terms of their effects, going from nutritional to pharmacological to toxic.”
Scientists now have a fairly good understanding of antinutrients’ mechanisms of action, but more research is needed to better understand their role in human health. Ironically, some compounds on the list of antinutrients are now referred to as “nutraceuticals” or “functional foods” because of their demonstrated beneficial effects on human health.
Perhaps in the near future, the chapter on antinutrients in nutrition textbooks will bear another name.
— Sharon Palmer, RD, is a contributing editor at Today’s Dietitian and a freelance food and nutrition writer in southern California.