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That foods might provide therapeutic benefits is clearly not a new

concept. The tenet, “Let food be thy medicine and medicine be thy food”

was embraced 2500 years ago by Hippocrates, the father of medicine.

However, this “food as medicine” philosophy fell into relative obscurity

in the 19th century with the advent of modern drug therapy. In the 1900s,

the important role of diet in disease prevention and health promotion came

to the forefront once again.


During the first 50 years of the 20th century, scientific focus was on the

identification of essential elements, particularly

vitamins

, and their role in the prevention of various dietary deficiency

diseases. This emphasis on nutrient deficiencies or “undernutrition”

shifted dramatically, however, during the 1970s when diseases linked to

excess and “overnutrition” became a major public health concern. Thus

began a flurry of public health guidelines, including the Senate Select

(McGovern) Committee's Dietary Goals for the United States (1977), the

Dietary Guidelines for Americans (1980, 1985, 1990, 1996, 2000— a joint

publication of the USDA and the Department of Health and Human Services),

the Surgeon General's Report on Nutrition and Health (1988), the

National Research Council's Diet and Health (1989) and Healthy People

2000 and 2010 from the U.S. Public Health Service. All of these reports are

aimed at public policy and education emphasizing the importance of

consuming a diet that is low in saturated fat, and high in vegetables,

fruits, whole grains and legumes to reduce the risk of chronic diseases

such as heart disease, cancer, osteoporosis, diabetes and stroke.


Scientists also began to identify physiologically active components in

foods from both plants and animals (known as phytochemicals and

zoochemicals, respectively) that potentially could reduce risk for a

variety of chronic diseases. These events, coupled with an aging, health-

conscious population, changes in food regulations, numerous technological

advances and a marketplace ripe for the introduction of health-promoting

products, coalesced in the 1990s to create the trend we now know as

“functional foods.” This report includes a discussion of how functional

foods are currently defined, the strength of the evidence both required and

thus far provided for many of these products, safety considerations in

using some of these products, factors driving the functional foods

phenomenon, and finally, what the future may hold for this new food

category.


What are functional foods?
All foods are functional to some extent because all foods provide taste,

aroma and nutritive value. However, foods are now being examined

intensively for added physiologic benefits, which may reduce chronic

disease risk or otherwise optimize health. It is these research efforts

that have led to the global interest in the growing food category now

recognized as “functional foods.”

Functional foods have no universally accepted definition. The concept was

first developed in Japan in the 1980s when, faced with escalating health

care costs, the Ministry of Health and Welfare initiated a regulatory

system to approve certain foods with documented health benefits in hopes of

improving the health of the nation's aging population (1). These foods,

which are eligible to bear a special seal, are now recognized as Foods for

Specified Health Use (FOSHU).3 As of July 2002, nearly 300 food products

had been granted FOSHU status in Japan.


In the United States, functional foods have no such regulatory identity.

However, several organizations have proposed definitions for this new food

category. In 1994, the National Academy of Sciences' Food and Nutrition

Board defined functional foods as “any modified food or food

healthcare

ingredients that may provide a health benefit beyond the traditional

nutrients it contains” (2). The International Life Sciences Institute

defines them as “foods that, by virtue of the presence of

physiologically-active components, provide a health benefit beyond basic

nutrition” (3). In a 1999 position paper, the American Dietetic

Association defined functional foods as foods that are “whole, fortified,

enriched, or enhanced,” but more importantly, states that such foods must

be consumed as “… part of a varied diet on a regular basis, at effective

levels ” for consumers to reap their potential health benefits (4).

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).