Reference
Brennan S, Cantwell M, Cardwell C, Velentzis L, Woodside J. Dietary patterns and breast cancer risk: a systemic review and meta-analysis. Am J Clin Nutr. 2010;91(5):1294-1302. [Epub ahead of print.]
Design
MEDLINE and EMBASE were searched for relevant articles that identified common dietary patterns published up to November 2009. Multivariable-adjusted odds ratios comparing highest to lowest categories of dietary pattern and multivariable adjusted ORs for a 20th percentile increase in dietary pattern scores were combined using random-effects meta-analyses.
Number of Studies
Case-control and cohort studies that identified prudent/healthy diet (N=18), Western/unhealthy diet (N=17), and drinker (N=4) dietary patterns. In total, 18 studies met the inclusion criteria and were included in the analyses.
Key Findings
This meta-analysis resulted in evidence of a decrease in the risk of breast cancer in the highest compared to the lowest categories of prudent/healthy dietary patterns (OR=0.89; 95% CI: 0.82, 0.99; P=0.02) in all studies and in pooled cohort studies alone. An increase in the risk of breast cancer was shown for the highest compared to the lowest categories of a drinker dietary pattern (OR=1.21; 95% CI: 1.04, 1.41; P=0.01). There was no evidence of a difference in the risk of breast cancer between the highest and the lowest categories of Western/unhealthy dietary patterns (OR=1.09; 95% CI:0.98, 1.22; P=0.12). A Western/unhealthy dietary pattern tended to have high quantities of red and/or processed meats, refined grains, potatoes, sweets, and high-fat dairy. Prudent/healthy diets tended to have high quantities of fruit, vegetables, poultry, fish, low-fat dairy, and whole grains.
Practice Implications
This study supports the long-held contention that diet provides breast cancer prevention. The data on this topic are mixed with some trials, such as the widely publicized randomized controlled Women’s Healthy Eating and Living (WHEL) trial on women with recently diagnosed early-stage breast cancer, which failed to show a benefit from diet in reducing breast cancer recurrence risk.1 Other trials have shown benefit, and follow-up analyses of the WHEL trial indicate that subgroups may experience benefit.2 The current meta-analysis provides a comprehensive opportunity to review the cumulative findings of trials on this association.
One important aspect of this meta-analysis is that the inclusion criteria studies are based on dietary patterns rather than on diets focused on single nutrients. This supports the hypothesis that nutrients in food have complex synergistic interactions and that their effects are best studied in a whole-foods context. Of interest is the lack of a difference in risk from Western/unhealthy diets in the highest compared to the lowest category.
One interpretation of this, in light of the observed benefit from the prudent/healthy diets, is that the absence of fruit, vegetables, poultry, fish, low-fat dairy, and whole grains is more impactful than the presence of deleterious foods.
One interpretation of this, in light of the observed benefit from the prudent/healthy diets, is that the absence of fruit, vegetables, poultry, fish, low-fat dairy, and whole grains is more impactful than the presence of deleterious foods. This makes sense when one considers the plentitude of DNA reparative, anti-inflammatory, antiproliferative and proapoptotic compounds found in healthy diets. When one is ingesting these compounds in sufficient quantity, one gains their protective effect, regardless of other components in the diet. While the risk reduction from healthy diets is small, namely a 7% risk reduction in cohort studies (OR=0.93; 95% CI: 0.88, 0.98; P=0.01), this is significant as both a cumulative factor and in association with other lifestyle parameters such as exercise. Another important conclusion from this meta-analysis is the once again clearly defined link between alcoholic beverage consumption (greater than 2 drinks daily) and increased breast cancer risk—above and beyond the underlying diet. Alcohol is thought to raise estrogen levels because of decreased hepatic clearance, to increase cellular susceptibility to carcinogens and to impair DNA repair enzymes.
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