Functional foods are foods that are believed to provide health benefits beyond the basic nutritional value of their macronutrients (protein, carbohydrates, and fats) by promoting optimal health, reducing the risk of certain diseases or conditions, or helping to treat health conditions. Functional foods are sometimes called nutraceuticals or medical foods.
The term “functional foods” is somewhat misleading because virtually all foods are functional in providing protein for muscle, carbohydrates for energy, and/or fatty acids, vitamins, and minerals for a variety of cellular and physiologic functions. Even foods with little nutritional value usually fulfill a function with their taste or aroma or by satisfying cravings. Furthermore, no generally agreed upon definition of functional foods has been developed, although most definitions include foods that have some physiological benefit over and above meeting basic nutritional needs. The United Nations Food and Agricultural Organization defines functional foods as “foodstuff that provides a health benefit beyond basic nutrition, demonstrating specific health or medical benefits, including the prevention and treatment of disease.” The Institute of Food Technologists' Expert Report defines functional foods as “foods and food components that provide a health benefit beyond basic nutrition (for the intended population)” and that provide “essential nutrients beyond quantities necessary for normal maintenance, growth, and development, and/or provide other biologically active components that impart health benefits or desirable physiological effects.” The Academy of Nutrition and Dietetics defines functional foods as “whole foods along with fortified, enriched or enhanced foods that have a potentially beneficial effect on health when consumed as part of a varied diet on a regular basis at effective levels based on significant standards of evidence.” Narrower definitions include only foods with nutrients such vitamins, minerals, fiber, probiotics, or prebiotics that have been added for a particular purpose. The U.S. Food and Drug Administration (FDA) regulates health claims for foods labeled as “functional” without defining the term, although the Orphan Drug Act of 1983 includes FDA regulation of specifically formulated medical foods and processed substances for dietary management of a disease or condition.
Functional foods have a long history. “Let food be thy medicine and medicine be thy food” is attributed to Hippocrates almost 2,500 years ago. The term “functional foods” was first introduced by the Japanese government in the 1980s to describe a class of conventional and modified or processed foods containing ingredients with added health benefits. As of 2018, Japan remained the only country with a specific regulatory approval process for foods for specified health use, covering about 100 products. Nevertheless, functional foods were one of the top food and nutrition trends in the United States in 2017. According to Google, “food with a function” was also one of the top five food trends of 2016, especially searches for jackfruit, kefir, and turmeric.
Depending on the definition, functional foods can include various conventional foods containing bioactive components, including:
Other functional foods may include:
Mushrooms are increasingly marketed as functional foods, and mushroom extracts are sold as dietary supplements or added to coffees and teas. Health claims for mushrooms and their extracts include stress reduction, stimulation of brain function, and cancer prevention, although evidence for such effects is very limited. Nevertheless, most edible mushrooms are high in nutrients, including fiber and antioxidants, and low in cholesterol. They have been used in Eastern medicine for centuries to treat conditions ranging from asthma to gout. In the laboratory, some medicinal mushrooms or their metabolites have been shown to have antioxidant and anti-inflammatory activities and even to improve recovery and function of damaged nerve cells.
Vitamins and minerals are micronutrients that are essential for health, have many well-defined physiologic functions, and are present in a wide range of foods. Additional health-promoting activities and optimal levels of these traditional micronutrients continue to be identified and defined or redefined. Thus, foods containing high levels of various vitamins and minerals are often classified as functional foods.
Specific types of macronutrients can also be functional constituents. For example, soy protein and monounsaturated fatty acids in tree nuts, olive oil, and canola oil may reduce the risk of coronary heart disease (CHD). Soy protein not only contains all nine essential amino acids and can function as a sole protein source, it also contains lunasin, a very small protein (peptide) that appears to increase the expression of genes that monitor for DNA damage and suppress the proliferation of tumor cells. Lunasin has been associated with reduced risk for several cancers, including prostate cancer, as well as reduced risk of heart disease. Essential omega-3 and omega-6 fatty acids must be obtained from the diet in foods such as olive oil and are necessary for growth, healthy skin, and cholesterol regulation, as well as absorption and transport of fat-soluble vitamins and carotenoids. The omega-3 fatty acids alpha-linolenic acid (ALA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA) may help maintain heart and eye health and mental function. DHA and EPA in cold-water fatty fish—such as salmon, tuna, mackerel, striped bass, halibut, sardines, trout, and flounder—and in fish oils may help lower cholesterol and triglycerides and help protect against CHD. DHA and EPA are also in certain fortified foods and beverages and dietary supplements. ALA is found in walnuts, flaxseed, and flaxseed oil. DHA is found in eggs from hens fed flaxseed, fish oil, or marine algae. Linoleic acids—omega-6 fatty acids from beef, lamb, and some cheeses—may help maintain body composition and immune system health.
Dietary fiber is another important functional constituent of many foods, especially whole grains. Soluble fiber in peas, beans, apples, citrus fruits, and psyllium seed husks promotes healthy blood glucose levels and may reduce risks for CHD and some types of cancer. Insoluble fiber in wheat bran, corn bran, and fruit skins helps maintain the digestive system and may reduce the risk of some types of cancer. Betaglucans are a complex group of soluble, viscous fiber consisting of readily fermentable glucose polymers (polysaccharides). Beta-glucans have a long history of medicinal uses for a variety of conditions and are known to lower blood cholesterol levels by several mechanisms. Beta-glucans slow digestion and improve nutrient absorption. By slowing the release of glucose into the bloodstream, beta-glucans can help control blood sugar levels and reduce the risk of type 2 diabetes. Beta-glucans are also prebiotics that promote the growth of beneficial colon bacteria that metabolize (ferment) them into short-chain fatty acids that the body can utilize as an energy source. Beta-glucans also can help fight inflammation and may lower blood pressure and reduce the risk of CHD. Beta-1,3-glucan may stimulate the immune system. Oats, barley, rye, mushrooms, yeast, and algae are good sources of beta-glucans.
Probiotics are live bacteria such as Lactobacilli (also called acidophilus) and Bifidobacteria in yogurts and other cultured dairy and nondairy foods, including fermented vegetables and soy products. They are similar or identical to bacteria normally residing in the human gut and are important for gastrointestinal health. Probiotics help maintain or restore a healthy balance of gut microflora and can help prevent or treat diarrhea and certain intestinal diseases. They are also thought to secrete protective substances that may stimulate the immune system to help prevent infection.
Phytochemicals or phytonutrients are functional constituents in plant foods.
There are no magical foods or superfoods that can compete with a healthy balanced diet and exercise for maintaining and improving health. Fortified foods with added nutrients should not be substituted for foods that naturally contain those nutrients. Furthermore, because the United States has no official definition of a functional food, consumers must evaluate health claims using Nutrition Facts labels and lists of ingredients on packaged foods.
Because functional foods can interfere with medications, complications can arise. Any patients taking medications or preparing for surgery need to request guidance from their doctors about foods to avoid or eat in limited quantities.
Often children prefer fortified, prepackaged foods to more healthful fruits and vegetables. To improve a child's diet or help combat overweight or obesity, parents need to be sure that their children are getting the right amounts of vitamins and minerals from healthy fresh foods, and that they are eating a balanced diet rather than relying on junk food.
See also Diet and disease prevention ; Macronutrients .
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Margaret Alic, PhD