Short Communication Effects of Dietary Weight Loss and Exercise on Insulin-Like Growth Factor-I and Insulin-Like Growth Factor-Binding Protein-3 in Postmenopausal Women: A Randomized Controlled Trial

High levels of insulin-like growth factor (IGF)-I may increase the risk of common cancers in humans. We hypothesized thatweight loss induced bydiet and/or exercisewould reduce IGF-I in postmenopausalwomen. Four hundred and thirty nine overweight or obese [bodymass index (BMI) 25 kg/m] women (50–75 years) were randomly assigned to: (i) exercise (N 1⁄4 117), (ii) dietary weight loss (N 1⁄4 118), (iii) diet þ exercise (N 1⁄4 117), or (iv) control (N1⁄4 87). Thediet interventionwas a group-basedprogramwith a 10%weight loss goal. The exercise intervention was 45 minutes/day, 5 days/week of moderate-to-vigorous intensity activity. Fasting serum IGF-I and IGF-binding protein (IGFBP)-3 were measured at baseline and 12 months by radioimmunoassay. Higher baseline BMI was associated with lower IGF-I and IGF-I/IGFBP-3 molar ratio. Although no significant changes in either IGF-I or IGFBP-3weredetected in any intervention armcomparedwith control, the IGF-I/IGFBP-3 ratio increased significantly in the diet (þ5.0%, P < 0.01) and diet þ exercise (þ5.4%, P < 0.01) groups compared with control. Greater weight loss was positively associated with change in both IGF-I (Ptrend 1⁄4 0.017) and IGF-I/IGFBP-3 ratio (Ptrend < 0.001) in the diet group, but inversely with change in IGFBP-3 in the diet þ exercise group (Ptrend 1⁄4 0.01). No consistent interaction effects with baseline BMI were detected. Modified IGF-I bioavailability is unlikely to be a mechanism through which caloric restriction reduces cancer risk in postmenopausal women. Cancer Epidemiol Biomarkers Prev; 22(8); 1457–63. 2013 AACR.