Overview of functional foods
Functional foods are defined as natural or modified foods that provide health benefits beyond basic nutrition. These foods can contain inherent health-promoting substances or have beneficial components added to them. The growing interest in functional foods stems from increased awareness of their medical advantages, the food industry's ability to innovate new products, and consumer willingness to incorporate these foods into their diets. Importantly, functional foods differ from nutraceuticals, which are active ingredients isolated from foods in medicinal forms, and phytochemicals, which are biologically active plant-derived substances.
Common examples of functional foods include fruits, vegetables, whole grains, nuts, and seeds, which possess active ingredients contributing to health. Specific categories of functional food components include probiotics, prebiotics, dietary fibers, omega-3 fatty acids, plant sterols, and carotenoids, all of which are associated with benefits such as improved gut health, reduced cholesterol levels, and enhanced antioxidant effects. While organizations like the American Dietetic Association and the Food and Agriculture Organization recognize the value of functional foods, consumers should critically assess health claims, as regulatory bodies like the FDA categorize these foods as such, not as drugs, limiting the claims manufacturers can make regarding disease prevention or treatment.
Overview of functional foods
DEFINITION: A natural or modified food or food component that provides a health benefit beyond basic nutrition.
Overview
Functional foods are whole foods that naturally contain health-promoting substances or contain added health-promoting substances. Also, functional foods can act in concert with herbal supplements and drugs in the prevention and treatment of disease. In contrast, nutraceuticals are active ingredients isolated from foods and prepared in a medicinal form, and phytochemicals are chemical substances obtained from plants that are biologically active but not nutritive.
The concept of functional foods is not new, as the medical and physiological benefits of some foods have been known for ages. The enhanced interest in functional foods is driven by a confluence of three factors: a greater understanding of the way functional food components exert medical benefits, the desire and capability of the food industry to produce new products based on these concepts, and interest and acceptance by the consumer. The modern discipline of functional food science places emphasis on gaining knowledge of how functional food components can affect certain body functions related to health and disease.
Several methods exist to modify a natural (unmodified) food to be a functional food. Any natural food with an active ingredient can be modified to improve its effectiveness as a functional food. For example, the concentration of a particular component that is naturally present in the particular food could be increased to produce beneficial effects. Similarly, a component known to cause a detrimental health effect could be removed. A component not normally found in a particular food but known to produce a beneficial effect could be added. A component whose intake is usually excessive and could cause deleterious health effects can be replaced by a component with beneficial health effects. Finally, the bioavailability or stability of a component known to reduce the disease-risk potential of a particular food could be improved.
The value of functional foods has been recognized by the American Dietetic Association, the Food and Agriculture Organization (FAO) of the United Nations, the International Food Information Council (IFIC), and many other organizations. However, consumers should carefully weigh the health claims and overall value of functional food products. The US Food and Drug Administration (FDA) considers functional foods as foods, not drugs, so manufacturers cannot claim that functional food can cure, mitigate, treat, or prevent any disease. The Nutrition Labeling and Education Act (1990) permits some exceptions, known as health claims, which state that a substance included in the diet on a regular basis “may help reduce the risk” of a certain disease. Most companies, however, prepare label claims based on maintaining a normal, healthy structure or function of the human body. Although so-called structure or function statements do not need approval from the FDA, the label must show a disclaimer statement to this effect. An example of a structure or function claim is the statement “helps build strong bones.”
Functional Food Types
In general, foods in their natural state, such as fruits and vegetables, oily fish, whole grains, nuts, and seeds, are among the best functional foods. They have active ingredients and a fine overall nutritional balance.
Probiotics and prebiotics. Probiotics are beneficial bacteria added to dairy products, such as yogurt, to improve gastrointestinal health. Prebiotics (oligosaccharide carbohydrates that are abundantly found in artichokes, shallots, and onions) are growth media for beneficial bacteria.
Polyphenols, anthocyanidins, flavones, and tannins. Polyphenols are found in a variety of foods. They have an antioxidant effect, thought to reduce the incidence of cancer and coronary heart disease. Anthocyanidins are found in fruits, catechins in tea, and flavones in citrus. Flavones are widely distributed in fruits and vegetables, and lignans are found in flax, rye, and some vegetables. Tannins are found in cranberries and cocoa, among other foods, and help lower oxidative stress and inflammation.
Dietary fibers. Dietary fibers, those food components obtained from plants that cannot be digested by the body, are classified as either insoluble or soluble. Insoluble fiber consists of plant cell-wall components, particularly cellulose, which form bulk in the diet and promote the regularity of bowel movements. Soluble fiber dissolves in water and thickens to form gels. Soluble fiber consistently has been shown to reduce total cholesterol and LDL (low-density lipoprotein), or bad cholesterol, in the blood. This reduction occurs through the reduced dietary fat and cholesterol uptake of the intestine and through increased fecal excretion of bile acids (which are derived from cholesterol).
Oats and barley contain an important fiber known as beta-glucan—a complex carbohydrate made of glucose units. Oatmeal has become a popular cereal for this reason, and oat bran, too, is marketed as a cereal or as an ingredient in other foods. Guar gum, pectin, and psyllium also contain abundant soluble fiber.
Omega-3 fatty acids. Omega-3 fatty acids are polyunsaturated fats that are beneficial for preventing heart disease and supporting healthy brain function. (Omega-3 refers to chemical structure.) The body cannot produce omega-3 fatty acids, so they must be ingested in foods or supplements. The omega-3 fatty acids eicosapentaenoic acid (EPA) and docosapentaenoic acid (DHA) are abundant in fatty fish, such as herring, anchovies, mackerel, salmon, and sardines. Another omega-3 fatty acid, alpha-linolenic acid (ALA), is found in chia seeds, edamame, beans, walnut oil, soybean oil, and canola oil. Fish oils have a more protective effect than plant-based sources of omega-3s. The body converts omega-3 fatty acids into biologically active compounds, such as prostaglandins and leukotrienes, which have anti-inflammatory, antithrombic, antiarrhythmic, and vasodilatory effects.
Plant sterols. Plant sterols are similar in structure to cholesterol and are found in the diet as sitosterol, stigmasterol, and campesterol. A compound made from sitosterol, known as stanol ester, is incorporated into a commercial margarine as a cholesterol-reducing agent. Nuts act as antioxidants and have a cholesterol-lowering effect.
Carotenoids. Carotenoids represent a large group of natural pigments found in plants (including yellow and orange fruits and vegetables, such as carrots, apricots, squash, and sweet potatoes) and in dark green vegetables, such as spinach, kale, and collard greens. The most common dietary carotenoids are alpha-carotene, beta-carotene, and lutein. Because of the nature of their molecules, carotenoids have strong antioxidant activity. Evidence shows that carotenoids have a protective effect against heart disease and some cancers.
Research
Most studies on functional foods have been observational because the great time and expense involved in clinical trials make observational studies the best option. Although there are many observational studies of functional foods, all attempt to relate the incidence of disease in a population with the dietary intake of a particular food. Observational studies can provide data from a large number of people in a relatively short period at a low cost, but these studies have been criticized for not controlling variables and for being subject to bias. Observational studies, however, can provide a strong indication of trends.
Intervention studies involve assigning participants to control or treatment groups, marked by various types and amounts of functional food components. The groups are followed over time, and researchers note the incidence of disease among groups. In a clinical trial, the groups are randomly assigned. Randomization reduces biases in the evaluation of treatment and control groups by making the groups equal in all respects except for the treatments applied.
Before beginning a study, researchers begin with basic scientific knowledge regarding functions that are sensitive to modification by food components. These functions could be genetic, cellular, biochemical, or physiological. Quite often, instead of examining the effect of the component on an outcome, researchers may use a marker that is related to the outcome. For example, researchers could study the effect of an ingredient on cholesterol levels instead of waiting for heart disease to develop. Markers must be able to predict the beneficial or detrimental effects of a food component. The body could respond to the intake of a food component through changes in body fluid levels of certain metabolites or enzymes. Measurement of changes in body tissues, such as the extent of narrowing of carotid arteries, can be related to the development of atherosclerosis. Markers need to be sensitive and specific to the disease condition.
Actions of Functional Foods and Their Components
Probiotics. Probiotics are bacteria established in the intestinal tract that exert a beneficial effect. The term “probiotics” was coined to contrast with antibiotics, which destroy harmful bacteria. Probiotics such as Lactobacilli and Bifidobacteria are normally added to dairy products. These bacteria promote improved intestinal microbial balance with a reduction in harmful microbes. Probiotics are beneficial in preventing infection and enhancing the immune system. They aid in preventing pathogens from entering the bloodstream through the mucosal epithelial cells by increasing mucin production and reducing permeability.
Probiotics also enhance the antibacterial and anti-inflammatory activities of the intestinal epithelium by stimulating the synthesis of specialized protective proteins. Clinical studies have shown that probiotics can reduce the symptoms of irritable bowel syndrome and can be beneficial in maintaining remission in cases of ulcerative colitis and pouchitis (inflammation of the intestinal wall). Other studies have shown that probiotics can help prevent necrotizing enterocolitis in infants.
Prebiotics. Prebiotics are indigestible oligosaccharide carbohydrates that can be fermented by lactobacilli and bifidobacteria. Prebiotics, along with probiotics, act in concert to produce the same beneficial results. Prebiotics can serve as fermenting media for probiotic bacteria already in the intestinal tract or in combination with introduced probiotics. Studies aim to determine appropriate conditions for the use of intact cereals as media for the growth of probiotic strains and to develop processing methods to isolate sources of water-soluble fiber that can serve as prebiotics.
Plant sterols. A review article indicated that plant sterols and tree nuts were beneficial for the prevention of coronary heart disease in most clinical trials, while flavonoids in dark chocolate may protect LDL cholesterol from undergoing oxidative modification. Plant sterols are believed to interfere with the absorption of cholesterol from the small intestine by preventing it from dissolving in the micellular structure. Plant sterols are added to margarine products as a cholesterol-lowering agent, but some consumers have concerns about weight gain. A meta-analysis of fifty-nine randomized clinical trials found that plant sterols that were added to milk, orange juice, or yogurt lowered total cholesterol and LDL cholesterol but did not do so when added to breads or meats.
Nuts. Many clinical studies have shown that the consumption of walnuts, almonds, pecans, pistachio nuts, and macadamia nuts result in lowered total cholesterol and LDL cholesterol. Epidemiological studies found an inverse relationship between nut consumption and the risk of coronary heart disease. Scientists believe that the beneficial effect of nuts comes from their high content of polyunsaturated fatty acids. Nuts may improve endothelial (blood-vessel wall) function too, resulting in better vasodilation. Nuts also may act as antioxidants, reducing LDL oxidation, one of the steps leading to plaque formation.
Polyphenols. Polyphenols, also known as flavonoids, are widespread in commonly consumed foods. Several hundred have been identified in fruits, vegetables, legumes, whole grains, and nuts as well as in beverages, such as tea, coffee, and wine. Many studies have examined polyphenols; however, many of these studies have been in vitro (in a laboratory) and at high doses. Epidemiological studies with humans have shown a protective effect of polyphenols on reducing fatal or nonfatal coronary artery disease. Epidemiological studies also have shown a protective effect against lung and colorectal cancers.
Procyanidins and isoflavones. Intervention (controlled) studies have shown that procyanidins found in red wine, grapes, cocoa, cranberries, and apples have pronounced beneficial effects on the vascular system, effects including antioxidant activity, decreased platelet aggregation, decreased LDL concentration, and increased HDL concentration. Isoflavones are plant compounds classified as phytoestrogens that are primarily found in soy. They are also found in legumes, many vegetables, and alfalfa, and they exist in large quantities in fermented soy products. Isoflavones may have effects on bone mineral density and bone mineral content in women who are postmenopausal. Other uses for isoflavones include reducing prostate cancer risk, reducing heart disease risk, and promoting hair and skin health.
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