The hypothesis that dietary antioxidants lower the risk of
chronic disease has been developed from epidemiologic studies
that consistently show that consumption of whole foods, such as
fruit and vegetables, is strongly associated with reduced risk of
chronic diseases. Therefore, it is reasonable for scientists to identify
the bioactive compounds responsible and hope to find the
“magic bullet” to prevent those chronic diseases. The key question
here is whether a purified phytochemical has the same health
benefit as the phytochemical present in whole food or a mixture of
foods. It is now believed that dietary supplements do not have the
same health benefits as a diet rich in fruit and vegetables because,
taken alone, the individual antioxidants studied in clinical trials
do not appear to have consistent preventive effects. The isolated
pure compound either loses its bioactivity or may not behave the
same way as the compound in whole foods. For example, numerous
investigations have shown that the risk of cancer is inversely
related to the consumption of green and yellow vegetables and
fruit. Because -carotene is present in abundance in these vegetables
and fruit, it has been extensively investigated as a possible
cancer-preventive agent. However, the role of carotenoids as anticancer
supplements has recently been questioned as a result of
several clinical studies (25–28). In one study, the incidence of
nonmelanoma skin cancer was unchanged in patients receiving a
-carotene supplement (25). In other studies, smokers gained no
benefit from supplemental -carotene (26) with respect to lung
cancer incidence and possibly even suffered a deleterious effect,