Differences in dietary intake are thought to account for approximately 30% of cancers in Western countries, although less in developing countries.10 Although many studies have examined the association of different dietary components on cancer risk, very few have examined the likely effect of changing the diet on subsequent risk or survival from cancer.
Early data showed that an increase in the polyunsaturated fatty acid concentration in membranes stimulated the oxidation of precarcinogens to reactive intermediates.11 The largest study to date, however, a pooled analysis on roughly 350,000 women, found no association between replacing monounsat-urated, polyunsaturated fats with carbohydrates on the incidence of breast cancer.12 In this same study, a weak positive association was identified between replacing saturated fats with carbohydrates on breast cancer incidence. There is little evidence linking dietary fat to the incidence of colorectal cancer. A single large randomized trial, however, showed no effect of a diet low in fat and high in fiber, fruit, and vegetables on the recurrence of colorectal adenomas.13
Fruit and vegetable intake is negatively associated with incidence of many cancers, including those of the oral cavity, esophagus, pharynx,14 stomach,15 colorectal region,16-18 lung,19 cervix,14 and kidney.14 Intervention trials, however, in which fiber and fruit and vegetable intake have been augmented, have failed to slow the recurrence of colorectal adeno-mas.13,20,21 Similarly, a study of beta-carotene supplementation failed to decrease the incidence of lung cancer.22 Similar to other food groups, very little evidence exists to understand the effect of changes of fruit and vegetable intake on cancer incidence. The three studies that have examined increases in fruit and vegetable intake, including the Polyp Prevention Trial as mentioned previously, have not found decrease in the recurrence of colorectal adenomas.13,20,21 An ongoing randomized trial, the Women's Healthy Eating and Living Study, will add to our understanding of the effect of a diet high in vegetables, fruits, and fiber and low in fat on breast cancer survival.23
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