Differential effects of fatness, fitness and physical activity energy expenditure on whole-body, liver and fat insulin sensitivity

Holt, H.B., Wild, S.H., Wareham, N., Ekelund, U., Umpleby, M., Shojaee-Moradie, F., Holt, R.I.G., Phillips, D.I. and Byrne, C.D. (2007) Differential effects of fatness, fitness and physical activity energy expenditure on whole-body, liver and fat insulin sensitivity. Diabetologia, 50 (8), 1698-1706. (doi:10.1007/s00125-007-0705-1).

Abstract

AIMS/HYPOTHESIS: The relative contributions of fitness (maximal oxygen uptake), physical activity energy expenditure (PAEE) and fatness to whole-body, liver and fat insulin sensitivity is uncertain. The aim of this study was to determine whether fitness and PAEE are associated with whole-body, liver and fat insulin sensitivity independently of body fat.

MATERIALS AND METHODS: We recruited 25 men (mean [SD] age 53 [6] years). Whole-body (M value) and liver (percentage suppression of endogenous glucose output) insulin sensitivity were estimated using a hyperinsulinaemic-euglycaemic clamp. Insulin sensitivity in fat (insulin sensitivity index for NEFA) was estimated during an OGTT. Total and truncal fat were measured by dual-energy X-ray absorptiometry, fitness by treadmill, and PAEE (n = 21) by 3 day heart rate monitoring and Baecke questionnaire.

RESULTS: In univariate analyses, fatness was strongly associated with insulin sensitivity (whole-body, liver and fat). Fitness was associated with whole-body (r = 0.53, p < 0.007) and liver (0.42, p = 0.04) insulin sensitivity, while PAEE was associated with liver insulin sensitivity (r = 0.55, p = 0.01). Regression models were established to describe associations between fatness, fitness and physical activity and measures of insulin sensitivity (whole-body, fat and liver) as outcomes. Only fatness was independently associated with whole-body insulin sensitivity (B coefficient -0.01, p = 0.001). Fitness was not associated with any outcome. Only PAEE was independently associated with liver insulin sensitivity (B coefficient 13.5, p = 0.02).

CONCLUSIONS/INTERPRETATION: Fatness explains most of the variance in whole-body insulin sensitivity. In contrast, PAEE explains most of the variance in liver insulin sensitivity.

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Contributors

Author: R.I.G. Holt

Author: C.D. Byrne

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