Phytochemical health benefits of fruit and vegetables

"Eat to Live, Not Live to Eat"
John H Weisburger, 2000

Liu, American Journal of Clinical Nutrition (2003) 78, S175-S205

Cardiovascular disease and cancer are ranked as the first and second leading causes of death in the US and in most industrialized countries. Regular consumption of fruit and vegetables is associated with reduced risks of cancer, cardiovascular disease, stroke, Alzheimer disease, cataracts, and some of the functional declines associated with aging. Prevention is a more effective strategy than is treatment of chronic diseases. Functional foods that contain significant amounts of bioactive components may provide desirable health benefits beyond basic nutrition and play important roles in the prevention of chronic diseases. The key question is whether a purified phytochemical (eg vitamin C) has the same health benefit as does the whole food or mixture of foods in which the phytochemical is present. We found, for example, that the vitamin C in non-skinned apples accounts for only 0.4% of the total antioxidant activity, suggesting that most of the antioxidants come from phenolics and flavonoids. We propose that the additive effects of the numerous phytochemicals in fruit and vegetables are responsible for their potent antioxidant and anticancer activities, and that the benefit of a diet rich in them is attributed to the complex mixture of phytochemicals present in whole foods.

This study illustrates why the common emphasis on food content of just the small number of commonly known vitamins usually misses the bigger picture. Consider vitamin C where oranges are often regarded as the reference standard for other fruits, with about 50mg/100g flesh. Apples (non-skinned) have less than a tenth this level, but when all antioxidant components in each are included they're approximately three times higher. The report also suggests why taking supplements is nowhere near as good nutritionally as consuming whole foods. About 5000 non-nutritive (ie not carbohydrates, proteins etc) phytochemicals have so far been characterised in plant products, but many thousands still remain unidentified. Activity differences between the common vitamins and whole foods are further accentuated as some of these less familiar phytochemicals can interact synergistically - ie their combined effects are greater than expected by simple addition.

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