Background: The association between risk of breast cancer and dietary fat and intakes of other energy sources remains controversial. The Italian population offers special opportunities to assess the influence of high intakes of unsaturated fat and starch and, because the population has low awareness of diet and cancer issues, there is less scope for recall bias. We have assessed the relations of various macronutrient intakes with risk of breast cancer.
Methods: In this case-control study, 2569 women with incident breast cancer (median age 55 years) and 2588 control women (median age 56 years) in hospital with acute, non-neoplastic diseases, were interviewed in six different areas of Italy between 1991 and 1994. A validated food-frequency questionnaire was used. It included questions on 78 foods and recipes grouped into six sections, as well as specific questions on individual fat intake pattern.
Findings: The risk of breast cancer decreased with increasing total fat intake (trend p 0.01) whereas the risk increased with increasing intake of available carbohydrates (trend p = 0.002). The odds ratios for women in the highest compared with the lowest quintile of energy-adjusted intake were 0.81 for total fat and 1.30 for available carbohydrates. Starch was the chief contributor to the positive association with available carbohydrates. High intakes of polyunsaturated and unsaturated fatty acids (i.e., polyunsaturated fatty acids plus oleic acid) were associated with a decreased risk of breast cancer (odds ratios for highest vs lowest quintile 0.70 and 0.74, respectively). Conversely, the intakes of saturated fatty acids, protein, and fibre were not significantly associated with breast-cancer risk.
Interpretation: This case-controls study shows that unsaturated fatty acids protect against breast cancer, possibly because intake of these nutrients is closely correlated with a high intake of raw vegetables. The findings also suggest a possible risk in southern European populations, of reliance on a diet largely based on starch.