Low-fat Dietary Pattern and Pancreatic Cancer Risk in the Women's Health Initiative Dietary Modification Randomized Controlled Trial

Background: Observational studies suggest that diet may influence pancreatic cancer risk. We investigated the effect of a low-fat dietary intervention on pancreatic cancer incidence. Methods: The Women's Health Initiative Dietary Modification (WHI-DM) trial is a randomized controlled trial conducted in 48 835 postmenopausal women age 50 to 79 years in the United States between 1993 and 1998. Women were randomly assigned to the intervention group (n = 19 541), with the goal of reducing total fat intake and increasing intake of vegetables, fruits, and grains, or to the usual diet comparison group (n = 29 294). The intervention concluded in March 2005. We evaluated the effect of the intervention on pancreatic cancer incidence with the follow-up through 2014 using the log-rank test and multivariable Cox proportional hazards regression model. All statistical tests were two-sided. Results: In intention-to-treat analyses including 46 200 women, 92 vs 165 pancreatic cancer cases were ascertained in the intervention vs the comparison group (P =.23). The multivariable hazard ratio (HR) of pancreatic cancer was 0.86 (95% confidence interval [CI] = 0.67 to 1.11). Risk was statistically significantly reduced among women with baseline body mass indexes (BMIs) of 25 kg/m(2) or higher (HR = 0.71, 95% CI = 0.53 to 0.96), but not among women with BMIs of less than 25 kg/m2 (HR = 1.62, 95% CI = 0.97 to 2.71, Pinteraction =.01). Conclusions: A low-fat dietary intervention was associated with reduced pancreatic cancer incidence in women who were overweight or obese in the WHI-DM trial. Caution needs to be taken in interpreting the findings based on subgroup analyses.