Dr. Ross Prentice, member of the Cancer Prevention and Biostatistics programs at Fred Hutch and his colleagues in the Women's Health Initiative originally launched the Dietary Modification Trial in 1993. The study involved nearly 49,000 postmenopausal women across the U.S. to test whether a low-fat dietary pattern would reduce the risk of breast and colorectal cancers and coronary heart disease. After nearly nine years of dietary change, they found that the low-fat diet did not significantly impact outcomes for these conditions. However, after longer-term follow-up of nearly 20 years, researchers found significant benefits, derived from modest dietary changes emerged and persisted including:

• A 15-35% reduction in deaths from all-causes following breast cancer
• A 13-25% reduction in insulin-dependent diabetes
• A 15-30% reduction in coronary heart disease among 23,000 women without baseline hypertension or prior cardiovascular disease

"The WHI's Dietary Modification Trial has provided women with nutrition and disease prevention insights for some years," Prentice said. "The latest results support the role of nutrition in overall health, and indicate that low-fat diets rich in fruits, vegetables and grains have health benefits without any observed adverse effects."

Unlike other studies examining the link between diet, cancer and other diseases, WHI investigators designed the study as a long-term, randomized controlled clinical trial to limit bias and establish causal conclusions. Participants made intentional dietary changes resulting from learned integrated concepts about nutrition and behavior, taught by trained nutritionists during the first year and reinforced quarterly for nearly a decade.

"The sheer number of new diets and nutrition trends can be overwhelming to people who simply want to know, 'What should I be eating?'" said Dr. Garnet Anderson, a co-author of the study and senior vice president and director of Fred Hutch's Public Health Sciences Division. She also serves as principal investigator of the Fred Hutch-based WHI Clinical Coordinating Center. "While there are many diets that provide short-term benefits like weight loss, this study scientifically validates the long-term health effects of a low-fat diet."