Significant weight loss through calorie restriction, but not moderate weight loss through a low-fat diet, was linked to reduced breast cancer growth in a preclinical study presented at the 2016 American Association for Cancer Research Annual Meeting.1

This study examined weight loss through 4 different diets in mouse models of breast cancer. Although tumor size did not differ between obese mice and obese mice that returned to a normal weight on a low-fat diet, they did find that obese mice that lost significant amounts of weight on 3 calorie-restricted diets had smaller tumors.

“Based on our results, it appears that the degree of calorie restriction, and hence the amount of weight lost, matters more than the specific dietary changes used to generate the weight loss,” said Laura Bowers, PhD, a postdoctoral fellow in the University of North Carolina (UNC) Lineberger Cancer Control Education Program in Chapel Hill, and first author of the study.

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“Our findings are too preliminary to make any kind of recommendation for people. The overall message is that the breast cancer-promoting effects of chronic obesity may not be easily reversible with moderate weight loss, but more severe weight loss diets may be effective regardless of whether carbohydrate or fat is restricted.”

The study randomized mice to either maintain a normal weight or become obese by consuming a high calorie diet for 15 weeks. The obese mice were then randomly selected to lose weight across 10 weeks on 1 of 4 diets: unrestricted consumption of a low-fat diet; a high-carbohydrate diet or low-carbohydrate diet, both with a 30% reduction in calories per day; or the increasingly popular 5:2 diet involving intermittent reduction of calorie intake by 70% on 2 days per week.

Mice on the low-fat diet returned to a normal weight and body fat percentage, while mice in the other 3 weight-loss groups weighed significantly less than mice that had maintained a normal weight throughout the study.

When tumor growth was compared between the groups, mice in the obese group had greater tumor volume and weight compared to mice that maintained a normal weight throughout study. However, despite returning to a normal weight, tumor size in the mice on the low-fat diet was equivalent to the mice that remained obese. Mice on the 3 calorie restricted diets had smaller tumors than both obese and low-fat diet mice.

“This is an issue of increasing importance as the obesity epidemic in the United States and throughout the world is increasing the prevalence of obesity-related cancers, and obesity also makes cancers more deadly,” said Stephen Hursting, PhD, MPH, a UNC Lineberger member and professor in the UNC Gillings School of Global Public Health and the UNC Nutrition Research Institute, and senior author of the study. “We are working to identify mechanism-based interventions in our experimental models that can reverse the adverse effects of chronic obesity on cancer burden.”

Bowers emphasized the need for additional studies to further clarify whether diet type is linked to tumor size.


1. Bowers LW, Rossi EL, Shamsunder MG, Hursting SD. The pro-tumorigenic effects of obesity are reversed by severe weight loss via chronic or intermittent calorie restriction but not weight normalization via a low-fat diet. Poster presentatation at: American Association for Cancer Research Annual Meeting; April 16-20, 2016; New Orleans, LA. Abstract 4321.