Moderate changes in energy balance combined with exercise do not alter insulin-like growth factor I or insulin-like growth factor binding protein 3

This study was designed to investigate the impact of negative (NEG) and positive (POS) energy balance (BAL) on serum concentrations of insulin-like growth factor (IGF)-I and IGF binding protein (IGFBP)-1 and relative amounts of serum IGFBP-3 during 5 days of physical activity. Eleven men (23.6 ± 0.7 years) were assigned to 1 of 3 trials in a random, crossover design. Trials consisted of varying energy intake (NEG, −2092; BAL, balanced; POS, +2092 kJ/d) but with equal proportions of carbohydrates (50%), protein (30%), and fat (20%). Each subject ran daily on a treadmill at 65% to 70% of Vo2max for approximately 30 minutes. Blood samples were obtained each morning for the measurement of serum concentrations of IGF-I, IGFBP-1, and relative amounts of serum IGFBP-3. Body weight changes were significantly different from zero during the NEG and POS trials but not for BAL (NEG, −0.5 ± 0.1 kg [P = .03]; POS, 0.6 ± 0.2 kg [P = .05]; BAL, 0.2 ± 0.2 kg). Baseline serum concentrations of IGF-I were not different among trials (NEG, 188.7 ± 8.8 ng/mL; BAL, 169.7 ± 8.8 ng/mL; POS, 175.7 ± 8.8 ng/mL) nor were they different after the diet intervention (NEG, 155.7 ± 10.0 ng/mL; BAL, 172.4 ± 8.8 ng/mL; POS, 165.4 ± 8.8 ng/mL). Relative amounts of serum IGFBP-3 at baseline were not different between treatments for the 52-kDa IGFBP-3 isoform (NEG, 0.94 ± 0.05; BAL, 0.88 ± 0.05; POS, 0.81 ± 0.05 ADU) or for the 47-kDa IGFBP-3 isoform (NEG, 0.94 ± 0.02; BAL, 0.83 ± 0.02; POS, 0.79 ± 0.02 ADU) and were not different after 5 days of exercise and diet. Alterations in energy BAL resulted in no difference in IGFBP-1 concentrations between trials IGFBP-1 (PRE—NEG, 20.3 ± 3.3 ng/mL; BAL, 23.3 ± 4.9 ng/mL; POS, 21.2 ± 2.9 ng/mL) (POST—NEG, 27.6 ± 4.8 ng/mL; BAL, 24.9 ± 3.8 ng/mL; POS, 19.72 ± 2.2 ng/mL). However, the change in IGFBP-1 was significantly different from zero during the NEG trial but not for the POS or BAL trials (NEG, 8.9 ± 3.2 ng/mL [P = .03]; BAL, 0.97 ± 3.0 ng/mL; POS, −1.7 ± 3.8 ng/mL). An energy deficit or surplus of 2092 kJ in conjunction with daily aerobic exercise is not sufficient to impact serum concentrations of IGF-I or IGFBP-3, but a 2092-kJ deficit may alter serum concentrations of IGFBP-1 levels in healthy, college-aged men.