Author: Winston Craig, MPH, PhD, RD.
During the past decade, consumers have begun to view food in a new way. Different foods have been identified as containing health-promoting properties beyond the basic nutritional value of the food. These foods became known to nutrition scientists as functional foods.
Functional foods include tomatoes which contain lycopene, broccoli and cauliflower that contain isothiocyanates, oats which contains beta-glucans, carrots and sweet potatoes which contain carotenoids, spinach and other green vegetables contain lutein, while soy contains isoflavones.
But are these nutraceuticals safe and effective? Should we secure the health-promoting phytochemicals from the consumption of whole foods or from the nutraceuticals? There is so much to learn yet about the phytochemicals in our food.
What is the effective dose we need to achieve the health-promoting effects? Are supplements as effective as food, more effective, or less effective than food? Are there synergistic effects between similar phytochemicals in our food? Is the food matrix necessary for effective absorption? Are the phytochemicals altered by food processing? What dose causes toxicity?
There are scores of carotenoids and hundreds of flavonoids present in our food. Which members of these two families of pigments are best absorbed and which ones are the most biologically active? The answers may determine which ones would be packaged as nutraceuticals.
The dietary intake of beta-carotene-rich foods correlates with a reduced risk of various cancers. And so, why not just give people beta-carotene supplements rather than trying to get them to eat foods rich in beta-carotene? Well, several large cancer prevention trials involving beta-carotene have yielded disappointing results. When 20 to 50 mg of beta-carotene was given to subjects for periods of time ranging from 4 to 12 years, the risk of developing lung, prostate, colorectal, and other cancers significantly increased. Sounds like eating the beta-carotene rich foods would be the safest!
The consumption of a therapeutic margarine (such as Benecol, Take Control, or Smart Balance) that contains added plant sterol esters is an effective way to reduce elevated LDL cholesterol levels. However, this practice also depresses blood levels of carotenoids, which somewhat negates the value of the health-promoting effect of the plant sterols.
Tocotrienols are found in rice bran oil, olives, barley and oats. These phytochemicals reduce blood clots, lower LDL cholesterol levels and suppress the onset and proliferation of tumors. However, for full activity the tocotrienols must be fed at low concentrations. At high doses (as in supplements) they convert to alpha-tocopherol (the most common form of vitamin E) which diminishes the beneficial activity of the tocotrienols.
Numerous studies have confirmed that a regular intake of soy protein rich in isoflavones produces a significant decrease in blood cholesterol and triglyceride levels. However, no changes are observed in blood lipids when the isolated soy isoflavones are consumed. Analyses have also revealed that isoflavone supplements on the market are complex mixtures that are poorly standardized.
In summary, the health effects of whole foods tend to be more pronounced than those of the individual components they contain. The effectiveness and safety of nutraceuticals is uncertain at this time. Clinical trials examining the physiological effects of various nutraceuticals have met with mixed and sometimes disappointing results.