What are functional foods: A functional food is any food that
exerts health properties beyond the traditional nutrients it contains. There are two
categories of functional foods.
1. Foods that naturally contain biologically active, non-nutrient compounds that provide
health benefits. These compounds are phytochemicals, which are also sometimes called
nutraceuticals. Based on this definition, all plant foods could be considered
functional foods since they are all rich in phytochemicals or nutraceuticals
2. Food products specifically formulated to have higher amounts of nutrients or
phytochemicals than would naturally occur in that food. These are also called “designer
foods.”
Defining Nutraceuticals or Phytochemicals: Phytochemicals are
plant chemicals that differ from nutrients in some important ways. Essential
nutrients—which include protein, fats, minerals, and vitamins—are essential
for life. Without them, people develop acute deficiency disease symptoms that can eventually
cause death. Nutrients are found in all of the food groups.
Phytochemicals are not necessary for life but they help to promote optimal health by
lowering risk for chronic diseases, such as
cancer and heart disease. They are found
only in plant foods. Fruits and vegetables are among the best sources of these
compounds. Phytochemicals are believed to have many health benefits.
Some groups of phytochemicals that have been linked to decreased
cancer risk include:
Allyl sulfides, which may stimulate activity of enzymes that help to eliminate
toxic compounds and are found in onions, scallions, and leeks.
Dithiolthiones and isothiocyanates, which may increase activity of enzymes that
help to detoxify carcinogens and are found in the cruciferous family of vegetables—broccoli, cauliflower, Brussels sprouts, cabbage,
turnips, and others.
Indoles, which may interfere with estrogen metabolism and therefore could reduce
risk for some estrogen-related cancers such as breast cancer. They are also found in
cruciferous vegetables.
Isoflavones, which are found in soy foods and have a number of effects that may
affect cancer risk.
Lignans, which are found in rye and
flaxseed and may reduce breast cancer risk because they act as anti-estrogens.
Flavonoids are a special class of
phytochemicals that includes hundreds of different compounds. Most are excellent antioxidants and some have hormonal properties. Among
some of the most studied flavonoids are
quercetin, which is found in tomatoes, potatoes, broccoli, and onions and kaempferol,
which is found in kale and endive.
Carotenoids are a group of
phytochemicals that act as pigments, giving plants their bright green, orange, yellow, red,
and blue colors.
Functional foods in the marketplace: In the past, foods were
commonly fortified with nutrients to help prevent specific nutritional deficiencies.
Technically, any fortified food could be considered a functional food. Some examples are iron-fortified cereals, vitamin D-fortified milk, and iodized salt. Today, many functional foods are aimed
at boosting intakes of phytochemicals to reduce risk for chronic disease like cancer and heart disease.
Examples of functional foods you can find at the store include:
Cereals and breads with added isoflavones
Fruit juices with herbs that have alleged immune-enhancing properties, such as echinacea
Margarine with added phytosterols, which help to reduce cholesterol
Advantages of functional foods: Some functional foods make it
easier to meet requirements for nutrients that are often deficient in American diets. The
addition of calcium to orange juice and the
B-vitamin folate to enriched flour are two
examples. Some functional foods make it possible to achieve higher intakes of nutrients or
phytochemicals than would be realistic with natural food sources of these compounds.
Possible disadvantages of functional foods: Functional foods
that contain added nutrients or phytochemicals may send confusing messages about how to plan
healthful diets. Calcium-fortified orange juice is an improvement on a food that is already
healthful. Calcium-fortified candy or fiber-enriched white bread, on the other hand, involve
addition of beneficial substances to foods that are otherwise devoid of healthful
properties.
Manufactured functional foods cannot duplicate all of the benefits of whole plant foods,
some of which are not yet known. For example, plant foods like leafy green vegetables, which
are naturally rich in calcium, also provide
vitamin K and vitamin C, both of which are
needed for healthy bones, as well as numerous nutrients and phytochemicals that protect
against chronic disease. A diet based on whole plant foods is likely to be more healthful than
one based on functional foods.
Best bet for healthful eating: Moderate amounts of
manufactured functional foods can provide some benefits to the diet and may help to reduce
disease risk. However, they don’t offer any benefits over well-planned diets based on
whole grains, fruits, and vegetables. Eating foods that are naturally
rich in a wide array of phytochemicals makes good nutrition sense, though. The best approach
to dietary planning is to use functional foods in moderation in addition to a healthful
diet.
Bibliography
Cody V, Middleton E, et al. Plant Flavonoids in Biology and
Medicine II: Biochemical, Cellular, and Medicinal Properties. Alan R Liss, Inc, NY,
1988.
Lampe JW. Health effects of vegetables and fruits: assessing
mechanisms of action in human experimental studies. Am J Clin Nutr
1999;70(suppl)475S-90S.
Messina M, Messina V. Nutritional Implications of Dietary
Phytochemicals. In: Dietary Phytochemicals in Cancer Prevention and Treatment. Plenum
Press. New York, 1996.
Pariza M. Functional foods: technology, functionality, and health
benefits. Nutrition Today. 1999;34:150–151.
Reddy BS, Rao CV, et al. Chemoprevention of colon carcinogenisis by
organosulfur compounds. Cancer Res. 1993;53:3493–8.
Steinmetz KA, Potter JD. Vegetables, fruit, and cancer.II:
Mechanisms Cancer Causes and Control 1991;2:427–442.
Van Poppel G, Goldbohm RA. Epidemiologic evidence for beta-carotene
and cancer prevention. Am J Clin Nutr 1995;62:1393S-1402S.
World Cancer Research Fund and American Institute for Cancer Research.
Food, Nutrition, and the Prevention of Cancer: a global perspective. AICR.
1999:Washington, DC.
You WC, Blot WJ, et al. Allium vegetables and the reduced risk of
stomach cancer. J Natl Cancer Inst. 1989;81:162–4.
The information presented in the Food Guide is for informational purposes
only and was created by a team of US–registered dietitians and food experts. Consult
your doctor, practitioner, and/or pharmacist for any health problem and before using any
supplements, making dietary changes, or before making any changes in prescribed medications.