Letters Section Editor: Robert M. Golub, MD, Senior Editor.
To the Editor: Baseline differences in serum estradiol, relatively few participants who met the dietary target of 20% or less energy from fat, and the exclusion of an exercise intervention from the dietary modification group of the WHI trial all made it less likely that an experimental difference in breast cancer outcomes would be obtained in the study by Dr Prentice and colleagues.1 Observational studies have consistently found serum estradiol levels in postmenopausal women to be associated with breast cancer risk.2 A meta-analysis of 13 short-term low-fat dietary intervention trials showed significant declines in serum estradiol levels, particularly when coupled with physical activity interventions and when the dietary target of energy from fat was 20% or less.3 Other evidence suggests that adherence to diets lower in fat and higher in fruits and vegetables are facilitated by exercise.4,5
McCarthy WJ, Kuo T. Low-Fat Diet and Risk of Breast Cancer. JAMA. 2006;296(3):278-279. doi:10.1001/jama.296.3.278-b