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Intramyocellular lipid content and insulin sensitivity are increased following a short-term low-glycemic index diet and exercise intervention.

Author(s): Haus JM, Solomon TP, Lu L, Jesberger JA, Barkoukis H, Flask CA, Kirwan JP

Affiliation(s): Dept. of Pathobiology, Lerner Research Institute, Cleveland Clinic, OH 44195, USA.

Publication date & source: 2011-09, Am J Physiol Endocrinol Metab., 301(3):E511-6. Epub 2011 Jun 28.

Publication type: Randomized Controlled Trial; Research Support, N.I.H., Extramural

The relationship between intramyocellular (IMCL) and extramyocellular lipid (EMCL) accumulation and skeletal muscle insulin resistance is complex and dynamic. We examined the effect of a short-term (7-day) low-glycemic index (LGI) diet and aerobic exercise training intervention (EX) on IMCL and insulin sensitivity in older, insulin-resistant humans. Participants (66 +/- 1 yr, BMI 33 +/- 1 kg/m(2)) were randomly assigned to a parallel, controlled feeding trial [either an LGI (LGI/EX, n = 7) or high GI (HGI/EX, n = 8) eucaloric diet] combined with supervised exercise (60 min/day, 85% HR(max)). Insulin sensitivity was determined via 40 mU.m(-2).min(-1) hyperinsulinemic euglycemic clamp and soleus IMCL and EMCL content was assessed by (1)H-MR spectroscopy with correction for fiber orientation. BMI decreased (kg/m(2) -0.6 +/- 0.2, LGI/EX; -0.7 +/- 0.2, HGI/EX P < 0.0004) after both interventions with no interaction effect of diet composition. Clamp-derived insulin sensitivity increased by 0.91 +/- 0.21 (LGI/EX) and 0.17 +/- 0.55 mg.kg(-1).min(-1) (HGI/EX), P = 0.04 (effect of time). HOMA-IR was reduced by -1.1 +/- 0.4 (LGI/EX) and -0.1 +/- 0.2 (HGI/EX), P = 0.007 (effect of time), P = 0.02 (time x trial). Although both interventions increased IMCL content, (Delta: 2.3 +/- 1.3, LGI/EX; 1.4 +/- 0.9, HGI/EX, P = 0.03), diet composition did not significantly effect the increase. However, the LGI/EX group showed a robust increase in the [IMCL]/[EMCL] ratio compared with the HGI/EX group (Delta: 0.5 +/- 0.2 LGI/EX vs. 0.07 +/- 0.1, P = 0.03). The LGI/EX group also demonstrated greater reductions in [EMCL] than the HGI/EX group (Delta: -5.8 +/- 3.4, LGI/EX; 2.3 +/- 1.1, HGI/EX, P = 0.03). Changes in muscle lipids and insulin sensitivity were not correlated; however, the change in [IMCL]/[EMCL] was negatively associated with the change in FPI (r = -0.78, P = 0.002) and HOMA-IR (r = -0.61, P = 0.03). These data suggest that increases in the IMCL pool following a low glycemic diet and exercise intervention may represent lipid repartitioning from EMCL. The lower systemic glucose levels that prevail while eating a low glycemic diet may promote redistribution of lipid stores in the muscle.

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