Ghrelin, glucose and insulin can be influenced by exercise and body composition, and have a role in appetite control. Although, it is well established that a single exercise bout improves glucose metabolism acutely, the effects appear to diminish within 48 to 72 h(Reference Ross1). The aim of this investigation was to assess the effects of (1) habitual exercise, and (2) a short-term exercise intervention on fasting ghrelin, glucose, insulin and HOMA-IR in men, and to explore associations with body fat and energy expenditure.
In the first cross-sectional study, forty-four men (Active: n = 22, Inactive: n = 22; range BMI 21–36 kg/m2; range percent fat mass 9–42 %) were studied. For the second study, a subset of fifteen inactive overweight men subsequently completed a 4-wk supervised exercise intervention, consisting of 5 exercise sessions per week on a cycle ergometer. Body composition was assessed by air displacement plethysmography, activity energy expenditure (AEE) by accelerometery and fasting levels of glucose, insulin and ghrelin were taken. The measurements were repeated (≥48 h) after the final exercise session in the second study.
Active and inactive men differed significantly for a number of characteristics including ghrelin, insulin and HOMA-IR (Table 1a). When the data were pooled (n = 44) the strongest correlates of fasting insulin and HOMA-IR were percent fat mass (r = 0·57 and r = 0·56, p < 0·01) and resting heart rate (r = 0·56 and r = 0·54, p < 0·01) and the strongest correlate of ghrelin was AEE (r = 0·33, p < 0·05).
Table 1a. n = 22 per group; Table 1b. n = 15 Pre/Post Intervention
Following the 4-wk exercise intervention in inactive males, despite a modest reduction in body weight and fat mass and 13 % increase in VO2max, fasting glucose, insulin and ghrelin were unchanged (Table 1b). Individual variability in response was explained mostly by changes in body fat, with changes in insulin and HOMA-IR from pre-to post-intervention being associated with changes in body fat (insulin: r = 0·69, p < 0·01; HOMA-IR: r = 0·70, p < 0·01). Change in glucose was negatively correlated with baseline glucose levels (r = −0·68, p < 0·01). Ghrelin did not correlate with changes in other variables or with baseline values.
In conclusion, fasting ghrelin is higher and insulin and HOMA-IR lower in active compared to inactive men. Despite significant improvements in VO2max, four weeks of exercise training did not alter these measures in inactive overweight men. In the absence of acute exercise effects, these markers may only adapt to a greater volume of exercise or changes in other characteristics associated with regular exercise including reduced fat mass. Findings support the view that exercise should be performed on a regular basis or to induce a greater reduction in fat mass to improve fasting insulin and HOMA-IR. Further work is required to examine implications of these findings for food intake regulation with exercise.
