Strong consumer interest in the relationship between diet and health has created an insatiable demand for nutrition information. Dietary antioxidants, because of their association with chronic disease risk reduction, are the basis of much of this intrigue.

Keeping pace with this demand has been a challenge. As health professionals and journalists strive to inform the public about these beneficial food components, academic, scientific and regulatory organizations have stepped up their efforts to meet the demand for research results and information.

At the October 1998 annual meeting of The American Dietetic Association (ADA), a session titled, Antioxidants: Scientific Status; Consumer Attitudes, addressed the scientific rationale for the development of definitions for these dietary components.

Antioxidants: Complex Compounds

By now, many have heard about epidemiological evidence suggesting that eating fruits and vegetables may reduce the risk of both cancer and cardiovascular disease. It has been hypothesized that these potential health benefits are due in part to the presence of antioxidant compounds in these foods. These beneficial compounds have been lumped together and loosely termed dietary antioxidants. However, further examination by scientists has revealed that compounds typically grouped together as dietary antioxidants can differ considerably from one another. Because of these differences, defining exactly what antioxidants are is no small task.

Scientists have learned that antioxidants are components of food, are found mostly in fruits and vegetables and prevent free radicals from attacking cells and damaging DNA. But, "developing a definition is complicated because the functions of some compounds vary under differing circumstances," stated ADA speaker, Sandra Schlicker, Ph.D., senior staff officer, Food and Nutrition Board, Institute of Medicine (IOM), National Academy of Sciences (NAS). "In addition, antioxidants in foods are not interchangeable and may differ from one another both in their sites of action and their mechanism of action." In other words, the beta carotene found in a carrot may not act in the same manner as the vitamin C found in oranges.

Scientists are working hard to figure out just what it is that makes these food components beneficial to health. In the meantime, because no set definition exists, researchers and others have tried to provide some framework with which to work.

Establishing a Definition

A number of academic, scientific and regulatory organizations are considering what research is needed to support claims and establish definitions related to antioxidants, or functional components of foods. At the ADA conference, John Milner, Ph.D., professor and head of the Department of Nutrition at the Pennsylvania State University, presented an overview of several antioxidants and other functional components believed to reduce the risk of major chronic diseases. While scientifically-sound research already indicates potential health benefits of dietary antioxidants, "much work still remains," noted Dr. Milner. "A large body of credible scientific research is needed to confirm the benefits of any particular food or component." Without enough research to answer various questions, accurate definitions cannot be established.

To date, according to Dr. Milner, more than 500 compounds have been identified as potential key components to a healthful diet. However, the number of compounds where ample information is available to establish their link to health is much smaller.

A recent report from the Panel of Dietary Antioxidants and Related Compounds, IOM, NAS, has proposed a definition for dietary antioxidants for the purpose of characterizing the properties of these compounds (see glossary). The Panel's proposed definition for antioxidants is based on several criteria. First, the substance must be found in human diets. Second, data on the food component must exist in measurable quantities in food consumption databases, such as the U.S. Department of Agriculture's Continuing Survey of Food Intakes by Individuals (CSFII). Last, the substance must have been shown, in humans, to decrease the adverse effects of free radicals (see glossary).

The more established functional food components-those where a greater wealth of science has indicated their promise as having possible antioxidant effects-are being reviewed by the NAS/IOM's Panel on Dietary Antioxidants and Related Compounds to establish Dietary Reference Intake levels (DRI) (see September/October 1998 Food Insight). The following compounds are being considered for DRI levels.

Carotenoids

Carotenoids are an array of compounds that include among others, beta-carotene, alpha-carotene, lycopene, lutein and zeaxanthin, and cryptoxanthin.

Vitamin C

Because vitamin C can donate electrons, it effectively prevents damage caused by free radicals. Its role as an antioxidant is well established through many animal and human studies.

Vitamin E

Vitamin E has long been known for its effectiveness as a scavenger of free radicals. Composed of a group of fat-soluble molecules that occur naturally in eight different forms, dietary vitamin E comes from both plant and animal sources. Evidence is mounting about the antioxidant effects of vitamin E on heart disease, and there is some preliminary research on its effects on some types of cancer. Studies using food and supplements show that vitamin E benefits healthy people, as well as those who already have heart disease.

Selenium

Selenium is an essential component of several enzymes that help remove free radicals from the blood stream. Intervention studies have demonstrated antioxidant effects of selenium supplementation on reducing the risk of disease development.

Other functional components of food, such as flavonoids, phenols and polyphenols, and phytoestrogens, are not currently under review by the NAS/IOM panel for DRIs. This is because there are few published scientific studies on these potentially important dietary substances. However, ongoing research may provide data on which to base future DRIs for these compounds.

Consumer interest is often the driver for further research and information. Quantitative research conducted by the International Food Information Council (IFIC) in 1998 shows that 91 percent of consumers interviewed want more information on the subject of functional food components, including antioxidants (see May/June 1998 Food Insight). "It is clear that consumers' curiosity is piqued," stated Lisa Katic, RD, associate director, food safety at IFIC. "The whole focus has shifted in the consumer's mind from family history as being the number one influence on health, to food and nutrition as being the number one contributing factor."

The ever-expanding body of knowledge on antioxidant and related compounds, while helping to clarify the role of these important food components, also complicates the issue of defining dietary antioxidants. However, one common theme to all of the suggested definitions for these food components is the assumption that they have a potentially beneficial role in risk reduction and treatment of disease.

Where Antioxidants are Found

• Carotenoids are found in fruits and vegetables including carrots, fresh tomatoes, tomato products, green vegetables, peppers and squash.
• Vitamin C is found in oranges and orange juice, peppers, tomatoes and many other fruits and vegetables.
• Vitamin E is found in nuts, fats and oils, wheat germ and green leafy vegetables.
• Selenium is mostly found in seafood and organ meats (liver, kidney).

For some of these vitamins and minerals, for example, vitamin E, it is difficult to get sufficient amounts of the nutrient from foods to receive true antioxidant effects. In such cases, supplements may be warranted.

Glossary

Dietary antioxidants (NAS/IOM proposed definition):

A dietary antioxidant is a substance in foods that significantly decreases the adverse effects of reactive oxygen species, reactive nitrogen species, or both on normal physiological function in humans.

Free radical:

Unstable molecules resulting from normal metabolic processes. During these processes, oxygen molecules lose an electron, which creates an unstable molecule (free radical) thereby causing oxidative stress. These free radicals attack healthy cells in the body in the hopes of finding another electron to stabilize themselves. This process can cause damage to healthy cells.

Functional food components:

Nutritive and non-nutritive compounds found in food that are thought to reduce the risk of disease or promote health.

Functional foods:

Foods that may provide a health benefit beyond basic nutrition.

Phytochemicals:

Naturally occurring constituents of plant foods which are currently under scientific investigation to determine their potential benefits for reducing the risk of potential health problems, including cancer, cardiovascular disease, rheumatoid arthritis, hypertension and others.

Consumer Research Data

• 91% of consumers interviewed want more information on the subject of functional food components, including antioxidants.
• Antioxidants were named by 15% of participants as "potentially reducing the risk of specific diseases or health concerns."
• The extent that the following factors maintain or improve health.
• • Food and Nutrition: 74%
  • Exercise: 64%
  • Family Health History: 41%