Foods that may have health benefits beyond the traditional nutrients that they contain are often called "functional foods." The concept of functional foods has become popular in recent years, first in Japan and later in other countries, including the U.S.
While it would be helpful if we could prevent a wide range of specific diseases by consuming certain foods, in most cases the science behind such an approach isn't very strong yet, and in some cases there is no scientific evidence at all.
In the U.S., the term "functional foods" has no official, universally accepted definition. Foods don't have to pass any test or meet any standard in order to be described as "functional." To help shed some light on the issue, a new report from the American Council on Science and Health, Facts About "Functional Foods", ranks a variety of functional foods health claims according to the strength of the scientific evidence.
In the U.S., the best way for consumers to find out whether a food has any scientifically established health benefits beyond basic nutrition is to look for a special type of statement called a "health claim" on the food label. Health claims must be pre-approved by the Food and Drug Administration (FDA) before they can be used. This differs from the procedure used for structure/function claims on the labels of foods or dietary supplements. Structure/function claims are expected to be truthful, but they do not require FDA pre-approval. While the scientific data underlying statements on various food packages are not equally reliable, it's a start.
ACSH classifies the strength of the scientific evidence for the benefits of various functional foods currently on the market as follows:
Very strong: whole oat products (lowered cholesterol levels and reduced heart disease risk), foods containing psyllium (lowered cholesterol levels and reduced heart disease risk), whole soy foods and foods made with soy protein (lowered cholesterol levels and reduced heart disease risk), special fortified margarines made with plant stanol or sterol esters (lowered cholesterol levels and reduced heart disease risk), sugarless chewing gums and candies made with sugar alcohols (do not promote tooth decay). The FDA has approved health claims for all of these products.
Strong: Fatty fish containing omega-3 fatty acids (reduced risk of heart disease).
Moderate: Cranberry juice (reduced risk of urinary tract infection), organosulfur compounds in garlic (lowered cholesterol levels).
Weak to moderate: Green tea (reduced cancer risk), lycopene in tomatoes and tomato products (reduced risk of some types of cancer, especially prostate cancer).
Weak: Dark-green leafy vegetables containing lutein (reduced risk of macular degeneration), meats and dairy products containing conjugated linoleic acid (various health benefits), cruciferous vegetables (reduced cancer risk), probiotics (beneficial effects on gastrointestinal function and immunity).
ACSH will update its information on functional foods as new research is done.
Safety concerns have been raised about some functional foods, especially foods containing added medicinal herbs. Concerns have also been raised about the possibility that the promotion of functional foods may mislead people into thinking that eating them is more important than choosing a balanced diet or taking other steps to prevent or treat health problems. Exaggerated claims for some functional foods and inconsistent regulations may contribute to consumer confusion.
Consumers need to be cautious and skeptical when evaluating claims made for functional food products. ACSH recommends that consumers who are interested in incorporating functional foods into a healthy lifestyle should first consider products that carry FDA-approved health claims. These foods have been convincingly demonstrated to be beneficial for their intended purposes when consumed as part of a generally well-balanced and healthful diet. Consumers who wish to try functional foods that do not carry FDA-approved health claims should realize that there is no substantial proof that these foods have the special benefits claimed for them.
Functional foods are only one aspect of diet, and diet is only one aspect of a comprehensive lifestyle approach to good health, which should include regular exercise, tobacco avoidance, maintenance of a healthy body weight, stress reduction, and other positive health practices. Functional foods can sometimes be part of an effective strategy to promote good health, but they should never be considered a substitute for other good health habits and they should never be used instead of medically prescribed therapy for any health problem.