Effects of a 9-month strength training intervention on insulin, insulin-like growth factor (IGF)-I, IGF-binding protein (IGFBP)-1, and IGFBP-3 in 30-50-year-old women

We assessed the effects of twice weekly strength training on several proposed risk factors for breast and colon cancer: body fat, waist circumference, fasting insulin, fasting glucose, insulin‐like growth factor I (IGF‐I), and several IGF‐binding proteins. Fifty‐four healthy women, 30‐50 years old, were randomized to no‐contact control or treatment: 15 weeks of supervised strength training followed by 6 months of unsupervised training. Fifteen‐week changes included reductions in percentage of body fat, fasting insulin, fasting glucose, and IGF‐I that were larger in the treatment than control participants (treatment versus control mean +/‐ SE: % body fat ‐1.97 +/‐ 0.42 versus ‐0.43 +/‐ 0.40, P = 0.01; insulin (uU/ml) ‐0.29 +/‐ 0.35 versus 0.81 +/‐ 0.38, P = 0.055; glucose (mg/dl) ‐1.92 +/‐ 1.27 versus 1.21 +/‐ 1.36, P = 0.13; and IGF‐I (ng/ml) ‐30.47 +/‐ 9.75 versus 5.86 +/‐ 10.44, P = 0.02). There was no treatment effect on IGF‐binding proteins 1 and 3 or either of two surrogate measures of free IGF‐I. By 39 weeks changes in percentages of body fat were largely maintained; IGF‐I returned to baseline levels in the treatment group but remained 15% lower in treatment compared with control participants. Strength training produced favorable changes in several proposed cancer risk factors. The importance of these changes to long‐term cancer prognosis, diagnosis, and/or recurrence remains to be determined.