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

P-value: Independent t-test (Table 1a), Paired t-test (Table 1b). ¹n = 19, ²n = 13.

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.