ARCHIVED - Health Canada Scientific Summary of the U. S. Health Claim Regarding Fruits, Vegetables and Cancer
Bureau of Nutritional Sciences
Food Directorate, Health Products and Food Branch
Since the U. S. Health Claim pertaining to low fat diets rich in fruits and vegetables and cancer risk reduction was accepted in 1993, subsequent new evidence continues to support the claim particularly regarding fruits and vegetables. A report by the World Cancer Research Fund and the American Institute for Cancer Research (WCRF/AICR, 1997) concluded that there was convincing evidence to support a protective effect of fruits and vegetables against many types of cancers. This conclusion was based on numerous case-control studies that showed that cancer patients consumed less fruit and vegetables than comparable control cancer-free groups. Fruits in their review excluded high starch plantains and bananas, and vegetables excluded high starch roots and tubers. Since potatoes are consumed in large quantities in most North American diets, the inclusion of potatoes as a vegetable could potentially confound the effect of vegetable intake. The WCRF/AICR, 1997 did not support the inclusion of the caveat "low fat diets" in the health claim, because, although a possible link exists, the evidence was not sufficient to make a definitive judgement. The evidence for a fat /cancer relationship will be examined elsewhere.
Current Canadian intakes of vegetables including juice but excluding potatoes and corn range between 140 (Nova Scotia) and 194 (Québec) g/d for adult men and women combined, and fruit intake including juices range between 164 (Nova Scotia) and 212 (Québec) g/d. Based on defined serving sizes, in the Québec survey, the average fruit and vegetable intake was 4 servings of fruit and vegetables /d. Potential benefits of increased fruit and vegetable consumption can be estimated indicating that relatively small increases in fruit and vegetable consumption may decrease the relative risk of lung and stomach cancers, for example.
A large number of case control studies conducted since 1997 and recent reviews consistently support that diets rich in fruits and vegetables reduce the risk of some types of cancer. Evidence from prospective cohort studies is supportive of the relationship for certain cancers and for certain fruit or vegetable groups, but not all. Given the association of overweight with all-cancer mortality, both energy intake and body mass index (BMI) should be controlled as potential confounders, but most studies control for only one of these factors. However, when one of these have been controlled, usually BMI, the significant independent effects of fruit and vegetable intakes remain. One very recent large randomized controlled trial did not show a significant reduction in colorectal adenomas over a 4 year period in older adults (mean age 61 years) with a history of adenomas consuming a low fat diet high in fibre, fruits and vegetables compared to controls; however, the effect of diet on cancer initiation versus cancer prevention has not yet been established.
Given the consistency of the epidemiological and other research on the cancer risk reduction of fruit and vegetables, a health claim stating that a diet rich in a variety of fruits and vegetables may reduce the risk of some types of cancer, a disease associated with many factors is warranted.* It is highly unlikely that non-dietary factors explain this reduction in risk. Although high starch roots and tubers may also provide valuable nutrients, there is insufficient evidence for the claim to be extended to these foods. There is not enough evidence to support a relationship between any one food component and reduced cancer risk.
*Important note: This claim was the subject of a regulatory amendment. For the final wording and conditions of use for this claim, please refer to the table following section B.01.603 in the Food and Drug Regulations.
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