Role of fat, animal protein, and dietary fiber in breast cancer etiology: a case-control study.

A case-control study of 818 breast cancer (BC) patients and 2 matched control groups, surgical controls (SCs) and neighborhood controls (NCs), was undertaken in Israel between 1975 and 1978. The interview schedule included a detailed dietary history based on the frequency of consumption of 250 food items, which were grouped according to their principal nutrient component. The average frequency of consumption of each food item in each nutrient group was computed. Medical, demographic, hormonal, and parity histories were also obtained. Risks associated with fat, animal protein, and fiber consumption were evaluated. Two types of analysis were performed [in 2 age groups (less than 50 yr and greater than or equal to 50 yr)], using the conditional logistic method: evaluating the risk attributable to nutrition only and controlling for nondietary confounding factors as well. When no adjustment for nondietary confounding factors was made, the risk increased with fat intake in both age groups [one-tailed P-value for linear trend = .08 and .07 in age less than 50 and .01 and .10 for the greater than or equal to 50 age category for the BC case (BCC)-SC and BCC-NC comparisons, respectively]. Increased fiber intake decreased the risk in the younger age group (one-tailed P-value for linear trend = .06 and .07 for the BCC-SC and BCC-NC comparisons, respectively), while in the 50-or-over age category the trend was inconsistent. The risk associated with animal protein was much less clear. For women in the highest quartiles of fat and animal protein intake and the lowest quartiles of fiber intake, risk was about twice as high as that for women in the lowest quartiles of fat and animal protein intake and in the highest quartile of fiber intake (one-tailed P-value for linear trend = .04 and .08 for age less than 50 and .08 and .09 for the age category greater than or equal to 50 BCC-SC and BCC-NC comparisons, respectively). When hormonal and demographic confounding factors were controlled for, this pattern persisted but it remained significant for 1 control only. Power increased when cases were analyzed against both controls simultaneously (one-tailed P-value for linear trend = .10 for age less than 50 and .02 for age greater than or equal to 50). Thus a higher fat-animal protein and lower fiber diet is associated with increased cancer risk, but this relationship needs to be studied further.