A study of insulin sensitivity in men : the association with fatty liver, cortisol metabolism and fitness

Abstract

In a group of middle-aged men we measured blood pressure, fasting lipids and glucose, BMI, waist circumference, skin fold thickness, total fat on DEXA, bioimpedance, and plethysmography and visceral fat on MRI.  We measured insulin sensitivity in muscle and liver using a euglycaemic, hyperinsulinaemic clamp technique with deuterated glucose, and suppression of non-esterified fatty acids during an oral glucose tolerance test.  We demonstrated that BMI and waist correlate strongly with measures of visceral and truncal fat and also to insulin sensitivity and other metabolic syndrome features.  We measured hepatic steatosis using ultrasonography and demonstrated that fatty liver is associated with impaired suppression of non-esterified fatty acids, independently of body fat, indicating that men with fatty liver have abnormal adipocytes function.

We found that a strong correlation between metabolism of cortisol measured by clearance of a tracer bolus of deuterated cortisol and insulin sensitivity in muscle and adipose tissue which was independent of body fat, suggesting that exposure to cortisol is higher in insulin-resistant individuals.

We measured fitness by oxygen uptake during maximal exercise, and physical activity energy expenditure using heart-rate monitoring.  We did not find that either fitness of energy expenditure were related to insulin sensitivity independently of body fat suggesting that the beneficial effects of exercise are mediated through changes in body composition.

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