Yet researchers agree that true disease protection lies not in any single compound, but within the intricate chemistry of entire foods. For example, Cornell University researchers found that orange juice extracts, minus their vitamin C, reduced precancerous lesi by 40 percent. This suggests that vitamin C is not working alone when it interferes with cancer growth. (I suspect whole oranges may have worked even better.) And last year, the results of the 12-year Physicians Health Study by Harvard University researchers showed no difference in risk of heart disease or cancer between 11,000 physicians who took beta-carotene pills and 11,000 of them who took a placebo. Nor was a protective effect for beta-carotene observed in two other large health trials. This suggests that beta-carotene alone has no disease-fighting effect.

Once the hundreds of beneficial compounds are properly identified and their interactions understood, you could take 100 pills a day and still not enjoy the same benefits. There is a much simpler and better-tasting option; eat lots of fresh fruits and vegetables.

Elizabeth Hiser is a nutritionist and writer about health issues.

Photography by Suzanne DeJohn/National Gardening Association