(27-08-10) Cardiorespiratory fitness and insulin sensitivity in overweight or obese subjects may be linked through intrahepatic lipid content.

Haufe S, Engeli S, Budziarek P, Utz W, Schulz-Menger J, Hermsdorf M, Wiesner
S, Otto C, Haas V, de Greiff A, Luft FC, Boschmann M, Jordan J.

Franz Volhard Clinical Research Center at Experimental and Clinical Research
Center, Charit? University Medical School and Max Delbr?ck Center for Molecular
Medicine, Berlin, Germany.
Abstract
OBJECTIVE: Low cardiorespiratory fitness (CRF) predisposes one to
cardiovascular disease and type 2 diabetes in part independently of body
weight. Given the close relationship between intrahepatic lipid content (IHL)
and insulin sensitivity, we hypothesized that the direct relationship between
fitness and insulin sensitivity may be explained by IHL. RESEARCH DESIGN AND
METHODS: We included 138 overweight to obese, otherwise healthy subjects (aged
43.6 +/- 8.9 years, BMI 33.8 +/- 4 kg/m(2)). Body composition was estimated by
bioimpedance analyses. Abdominal fat distribution, intramyocellular, and IHL
were assessed by magnetic resonance spectroscopy and tomography. Incremental
exercise testing was performed to estimate an individual's CRF. Insulin
sensitivity was determined during an oral glucose tolerance test. RESULTS: For
all subjects, CRF was related to insulin sensitivity (r = 0.32, P < 0.05), IHL
(r = -0.27, P < 0.05), and visceral (r = -0.25, P < 0.05) and total fat mass (r
= -0.32, P < 0.05), but not to intramyocellular lipids (r = -0.08, NS). Insulin
sensitivity correlated significantly with all fat depots. In multivariate
regression analyses, independent predictors of insulin sensitivity were IHL,
visceral fat, and fitness (r(2) = -0.43, P < 0.01, r(2) = -0.34, and r(2) =
0.29, P < 0.05, respectively). However, the positive correlation between
fitness and insulin sensitivity was abolished after adjustment for IHL (r =
0.16, NS), whereas it remained significant when adjusted for visceral or total
body fat. Further, when subjects were grouped into high versus low IHL, insulin
sensitivity was higher in those subjects with low IHL, irrespective of fitness
levels. CONCLUSIONS: Our study suggests that the positive effect of increased
CRF on insulin sensitivity in overweight to obese subjects may be mediated
indirectly through IHL reduction.

Source: Diabetes. 2010 Jul;59(7):1640-7. Epub 2010 Mar 31.

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