The Effects of Equivalent Weight Loss With or Without Exercise Training on Breast Cancer Risk (SHAPE-2)

Postmenopausal women who are sedentary or overweight, have an increased breast cancer risk. It is suggested that these two factors mediate breast cancer risk mainly through sex hormone-related pathways. However, an inactive lifestyle and obesity are highly correlated and it is not clear which is most relevant to risk. Literature shows that weight loss/ fat loss reduces postmenopausal sex hormone levels, but the question is if there is an additional beneficial effect on hormones of reaching this weight loss by physical activity instead of nutritional interventions. In this three-armed, two-center intervention study, 250 sedentary postmenopausal women who are aged 50-69 years will first enter a run-in period of 5 weeks. During this period, all participants get a diet, adapted to the guidelines for healthy nutrition, meeting their energy expenditures to maintain stable weight. After this run-in phase they are randomly allocated to a (1) diet induced weight loss group, (2) a combined exercise and diet induced weight loss group or (3) a control group. Participants allocated to the dietgroup will get a calorie restricted diet of -500 kCal/day, they will remain their habitual exercise pattern. Participants in the combined group will follow an exercise programme (combined endurance and strength) of 4 hours of sports per week with an average energy expenditure of 350 kCal/day and a, less strict. And a calorie restricted diet of -250 kCal/day. The aim of both intervention groups is to loose 5-6 kg of body weight during the 14 week intervention period. Participants in the control group are requested to retain the baseline diet and their habitual exercise pattern. Primary study parameters measured at baseline and after 21 weeks are: serum concentrations of endogenous estrogens, endogenous androgens and sex hormone binding globulin. Other study parameters include: body fat distribution, amount of total and abdominal fat, weight, BMI, physical fitness, blood pressure and lifestyle factors. The aim of this study is to provide insight into the effect of weight loss mainly driven by exercise compared to equivalent weight loss due to nutritional calorie restriction on breast cancer biomarkers. Furthermore, we are specifically interested whether weight loss mainly due to physical exercise induces greater amounts of fat loss (total and abdominal) and subsequently results in more favourable effects on these hormones compared to equivalent diet-induced weight loss.