But others said that even if the difference eventually becomes statistically significant with longer follow-up, the clinical importance of the reduction was questionable because the low-fat diet was linked with three fewer cases of invasive breast cancer for every 10,000 women followed per year.
“Even if a breast cancer effect is there, it's extremely small,” said Dr. Kuller at the conference. For understanding the biology of breast cancer, proving a link to dietary fat intake is very important, “but it's a very modest clinical effect.”
By contrast, Ross L. Prentice, Ph.D., lead investigator for the breast cancer analysis, said that even this small impact on breast cancer incidence is clinically meaningful. Because of the lag time in the development of breast cancer, it might take many years to see the full benefits of a reduced-fat diet, he said in an interview.
The difference in breast cancer incidence could become substantial if a reduced-fat diet was maintained over a lifetime, said Dr. Prentice, a professor of biostatistics at the University of Washington, Seattle, and a researcher at the Fred Hutchinson Cancer Research Center. “A low-fat diet is a reasonable choice for overall health, but we have not yet addressed what's the best diet to recommend.”