Functional Foods

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Essay title:  Functional Foods

Category: Issues and overviews

Related terms: neutraceuticals, phytochemicals

Definition: A functional food is a natural or modified food or food component that provides a health benefit beyond basic nutritional effects.


The concept of functional foods is not new, as medical and physiological benefits of some foods have been known for ages. The recent 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 new discipline of functional food science places emphasis in gaining knowledge of the means by which functional food components can affect certain body functions relating to health and/or disease. Functional foods must remain as foods consumed in usual amounts, and not as supplements or pills taken separately from foods. Neutraceuticals, on the other hand, are active ingredients isolated from foods and prepared as a medicinal form. Phytochemicals are chemical substances obtained from plants that are biologically active but not nutritive. Functional foods focus on entire foods that have active components such as phytochemicals. Functional foods can act in concert with supplements and drugs in the prevention and treatment of disease.

 An unmodified natural food with an active ingredient can serve as a functional food. Several types of modifications can be made to the natural food to improve its effectiveness as a functional food. The concentration of a component naturally present in the food could be increased to a point at which it will produce beneficial effects. A component known to cause a detrimental effect could be removed. A component not normally found in food but is known to produce a beneficial effect could be added. A component whose intake is usually excessive and could cause  deleterious effects is replaced by a component for which beneficial effects have been shown. Finally, the bioavailability or stability of a component known to reduce the disease-risk potential of the food could be improved.

 The value of functional foods has been recognized by the American Dietetic Association and many other organizations. However, the consumer must carefully weigh the health claims and overall value of functional food products. Basically, the Food and Drug Administration considers functional foods as foods not drugs, so companies cannot make any claim that functional foods can cure, mitigate, treat, or prevent any disease. The Nutrition Labeling and Education Act does permit 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 “structure/function” statements do not need FDA approval, the label must show a disclaimer statement to this effect.” An example of a structure/function” claim is to “help build strong bones.”

 Types of functional foods

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, since they have active ingredients and a fine overall nutritional balance.

 Probiotics are beneficial bacteria added to dairy products such as yogurt to improve gastrointestinal health. Prebiotics are oligosaccharide carbohydrates that are abundantly found in artichokes, shallots, and onions. Prebiotics serve as a growth medium for beneficial bacteria. Probiotics and prebiotics are discussed in the gastrointestinal health section.

 Polyphenols are found in a wide variety of foods. They have an antioxidant effect, reducing the incidence of cancer and coronary heart disease. Anthocyanidins are found in fruits, catechins in tea, and flavonones in citrus. Flavones are widely distributed in fruits and vegetables, and lignans are found in flax, rye, as well as some vegetables. Tannins are found in cranberries and cocoa. Epidemiological and clinical studies on polyphenols are described in a separate section.

 Dietary fiber refers to food components obtained from plants that cannot be digested by the body. Fiber is classified as either insoluble or soluble. Insoluble fiber consists of plant cell wall components, particularly cellulose, which form bulk in the diet and promote regularity of bowel movements. Soluble fiber dissolves in water and thickens to form gels. Soluble fiber has consistently been shown to reduce total cholesterol and LDL cholesterol in the blood. This reduction occurs by reduced dietary fat and cholesterol uptake by the intestine, and by increased fecal excretion of bile acids (which are derived from cholesterol). Oats and barley have 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 is also marketed as a cereal or as an ingredient for other foods. Guar gum, pectin, and psyllium also contain abundant soluble fiber.

 Omega-3 fatty acids have been found to be beneficial for the prevention of heart disease.Omega-3 refers to chemical structure. The omega-3 fatty acids, eicosapentaenoic acid and docosapentaenoic acid, are found in abundance in fatty fish, such as herring, anchovies, mackerel, salmon, and sardines. Another omega-3 fatty acid, linolenic acid, is found in walnut, soybean, and canola oils. The fish oils have a more protective effect than plant oils. Omega-3 fatty acids are converted to biologically active compounds such as prostaglandins and leukotrienes that have anti-inflammatory, antithrombic, antiarrythmic, and vasodilatory effects.

 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 margarines as a cholesterol reducing agent. Nuts act as antioxidants and have a cholesterol lowering effect. The modes of action of plant sterols and nuts are described in  the coronary heart disease section.

Carotenoids represent a vary large group of natural pigments found in plants. Carotenoids are found in yellow and orange colored 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. Due to the nature of the molecules, carotenoids have a strong antioxidant activity. There is evidence that carotenoids have a protective effect against heart disease and some cancers.

 Researching functional foods:

 Most studies on functional foods are observational in nature, due to the great time and expense involved in conducting a clinical trial. Although there are many types of  observational studies, they all attempt to relate 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 of  time at low cost; however, they are criticized for not being able control variables and are subject to bias. Observational studies, however, can still provide a strong indication of trends.  Intervention studies  involve assigning participants to control or treatment groups (various types and amounts of functional food components). The groups are followed over  time and the incidence of disease among groups is noted.  In a clinical trial, the groups are randomly assigned. Randomization reduces biases in evaluation of treatment and control groups by making the groups equal in all respects except for the treatments applied.

 Prior to beginning a study, researchers start with a basic scientific knowledge regarding functions that are sensitive to modification by food components. These functions could be genetic, cellular, biochemical or physiologic. 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 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 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.

 Functional foods and gastrointestinal health:

Probiotics are bacteria established in the intestinal tract that exert a beneficial effect. The term was coined to contrast with antibiotics which destroy harmful bacteria. Probiotics are normally added to dairy products as lactobacilli and bifidobacteria. These bacteria promote improved intestinal microbial balance with a reduction in harmful microbes.  Probiotics are beneficial in preventing infection and enhancing the immune system. Probiotics aid in preventing pathogens from entering the blood stream through the mucosal epithelial cells by increasing mucin production and reducing permeability. Probiotics also enhance antibacterial and anti-inflammatory activities of the intestinal epithelium by stimulating 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 are indigestible oligosaccharide carbohydrates that can be fermented by lactobacilli and bifidobacteria. Probiotics and prebiotics can therefore act in concert to produce the same beneficial results. Prebiotics can serve as a fermenting medium for probiotic bacteria already in the intestinal tract, or in combination with introduced probiotics. Studies are ongoing to determine appropriate conditions for the use of intact cereals as a medium for the growth of probiotic strains, or to develop processing methods to isolate sources of water-soluble fiber that can serve as prebiotics.

 Functional foods and coronary heart disease

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 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 questions about weight gain. A meta-analysis of 59 randomized clinical trials found that plant sterols added to milk, orange juice, or yogurt lowered total cholesterol and LDL cholesterol, but not when added to bread or meats.

 Numerous clinical studies have shown that 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 is due to their high polyunsaturated fatty acid content. Nuts may improve endothelial (blood vessel wall) function resulting in better vasodilation. Nuts may also act as an antioxidant, reducing LDL oxidation, one of the steps leading to plaque formation.


Polyphenols, also known as flavonoids, are very widespread in commonly consumed foods and several hundred have been identified in fruits, vegetables, legumes, whole grains, and nuts, and in beverages such as tea, coffee, or wine.  A large number of studies have been conducted on polyphenols; however, many have been in vitro (laboratory) studies at high doses. Epidemiological studies with humans have shown a protective effect of polyphenols on reducing fatal or nonfatal coronary artery disease. Epidemiological studies have also shown a protective effect against lung and colorectal cancer. Intervention (controlled) studies have shown that procyanidins found in red wine, grapes, cocoa, cranberries, and apples have pronounced beneficial effects on the vascular system including antioxidant activity, decreased platelet aggregation, decreased LDL concentration, increased HDL concentration, among other biomarkers. Isoflavones may have effects on bone mineral density and bone mineral content in post-menopausal women.

 David A. Olle, M.S.

 Further Reading

Institute of Food Technologists. “Functional Foods Expert Report: Opportunities and Challenges.” April 26, 2010. Describes in detail FDA regulations governing health related claims on food labels.

 Milner, John. “Functional Foods: the U.S. Perspective.” American Journal of Clinical Nutrition. 2000; 71 (supplement): 1654S-9S. An overview of functional foods including public interest and means of evaluation.

 Roberfroid, Marcel. “Concepts and Strategy of Functional Food Science: the European Perspective.” American Journal of Clinical Nutrition. 2000; 71 (supplement): 1660S-4S.

Provides an introduction into the development of functional foods and their applications.

 Saulnier, Delphine, et al. “Mechanisms of Probiosis and Prebiosis: Considerations for Enhanced Functional Foods.” Current Opinion in Biotechnology. 2009 April; 20 (2): 135-141. Discusses mechanisms and applications of probiotics and prebiotics.

Vita, Joseph. “Polyphenols and Cardiovascular Disease: Effects on Endothelial and Platelet Function.” American Journal of Clinical Nutrition. 2005; 81 (supplement): 292S-7S. A review of epidemiologic studies that support a relationship of higher intakes of polyphenolic flavonoids and reduced risk of cardiovascular disease.




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