Relationship between degree of obesity and in vivo insulin action in man

Abstract

Previous studies have demonstrated reduced in vivo insulin action in obese subjects compared with lean controls. However, little data is available on the relationship between degree of obesity and insulin action, and this relationship has not been shown to be independent of individual differences in maximal aerobic capacity. We studied 55 male Pima Indians and 35 male Caucasians with normal glucose tolerance. In vivo insulin action was measured using the hyperinsulinemic, euglycemic clamp technique at a plasma insulin concentration of approximately 100 microU/ml. Body composition was determined by densitometry, and maximal aerobic capacity was estimated using a graded exercise test. The results showed that degree of obesity was nonlinearly related to in vivo insulin action. In both Indians and Caucasians there was a significant decline in insulin action with increasing obesity up to a percent body fat of approximately 28-30%. Further increases in obesity in the Indians were not associated with significant changes in insulin action. Maximal aerobic capacity was positively linearly correlated with insulin action over the entire range of insulin action in both racial groups. Degree of obesity and maximal aerobic capacity were each independently associated with insulin action although these independent relationships were of marginal significance in the Caucasians. Surprisingly, individual differences in obesity and maximal aerobic capacity accounted for only half the variability observed in insulin action in these glucose tolerant subjects.

Skeletal muscle blood flow. A possible link between insulin resistance and blood pressure.

“…Because obesity is a major determinant of insulin resistance 4 -519 - 21 and hypertension, 22 -24 it is possible that our findings could be explained on the basis of the adiposity status of our study group. In this regard, it is important to point out that we found no correlation between MAP or IMGU with fat mass or percent body fat (Table 4).…”

Report of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus

“…Most patients with this form of diabetes are obese, and obesity itself causes some degree of insulin resistance (22,23). Patients who are not obese by traditional weight criteria may have an increased percentage of body fat distributed predominantly in the abdominal region (24).…”

Adipose tissue as a buffer for daily lipid flux

“…ranges of fatness [3,4,5]. Paradoxically, a deficiency of adipose tissue, as in lipodystrophy or lipoatrophy in humans [6,7] and rodents [8,9,10], is also associated with insulin resistance.…”