Another term often used interchangeably with functional foods, although it is less favored by consumers, is “nutraceuticals,” a term coined in 1991 by the Foundation for Innovation in Medicine to refer to nearly any bioactive component that delivers a health benefit. In a 1999 policy paper, Zeisel (5) astutely distinguished whole foods from the isolated components derived from them in his following definition of nutraceuticals: “those diet supplements that deliver a concentrated form of a presumed bioactive agent from a food, presented in a nonfood matrix, and used to enhance health in dosages that exceed those that could be obtained from normal food.”
Several factors are responsible for the fact that this is one of the most active areas of research in the nutrition sciences today: 1) an emphasis in nutritional and medical research on associations between diet and dietary constituents and health benefits, 2) a favorable regulatory environment, 3) the consumer self-care phenomenon, and 4) rapid growth in the market for health and wellness products.
Criteria for sound science
According to the Department of Health and Human Services, diet plays a role in 5 of 10 of the leading causes of death, including coronary heart disease (CHD), certain types of cancer, stroke, diabetes (noninsulin dependent or type 2) and atherosclerosis. The dietary pattern that has been linked with these major causes of death in the United States and other developed countries is characterized as relatively high in total and saturated fat, cholesterol, sodium and refined sugars and relatively low in unsaturated fat, grains, legumes, fruits and vegetables. An accumulating body of research now suggests that consumption of certain foods or their associated physiologically active components may be linked to disease risk reduction (6). The great majority of these components derive from plants; however, there are several classes of physiologically active functional food ingredients of animal or microbial origin.
Claims linking the consumption of functional foods or food advanced health ingredients with health outcomes require sound scientific evidence and significant scientific agreement. The Food and Drug Administration (FDA) outlined the criteria for “significant scientific agreement” in a guidance document released on December 22, 1999 (7). As summarized in the schematic shown in Figure 1, there is a clear discrepancy between “emerging evidence” (characterized by in vitro or animal studies, uncontrolled human studies, and inconsistent epidemiological evidence) and “significant scientific agreement.” To reach such agreement requires the support of a body of consistent, relevant evidence from well-designed clinical, epidemiologic and laboratory studies, and expert opinions from a body of independent scientists. Claims about the health benefits of functional foods should be based on sound scientific evidence, but too often only so-called “emerging evidence” is the basis for marketing some functional foods or their components. Table 1 categorizes a variety of functional foods according to the type of evidence supporting their functionality, the strength of that evidence and the recommended intake levels.
Functional foods of animal origin
Probably the most intensively investigated class of physiologically-active components derived from animal products are the (n-3) fatty acids, predominantly found in fatty fish such as salmon, tuna, mackerel, sardines and herring (8). The two primary (n-3) fatty acids are eicosapentaenoic acid (EPA; 20:5) and docosahexaenoic acid (DHA; 22:6). DHA is an essential component of the phospholipids of cellular membranes, especially in the brain and retina of the eye, and is necessary for their proper functioning. DHA is particularly important for the development of these two organs in infants (9), and just recently, the FDA cleared the use of DHA and arachidonic acid for use in formula for full-term infants (10). Hundreds of clinical studies have been conducted investigating the physiologic effects of (n-3) fatty acids in such chronic conditions as cancer, rheumatoid arthritis, psoriasis, Crohn's disease, cognitive dysfunction and cardiovascular disease (11), with the best-documented health benefit being their role in heart health. A recent meta-analysis of 11 randomized control trials suggests that intake of (n-3) fatty acids reduces overall mortality, mortality due to myocardial infarction and sudden death in patients with CHD (12).
