title: Intramyocellular lipid content and insulin sensitivity are increased following a short-term low-glycemic index diet and exercise intervention.
abstract: 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 × trial). Although both interventions increased IMCL content, (Δ: 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 (Δ: 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 (Δ: -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.
authors.affiliation: Dept. of Pathobiology, Lerner Research Institute, Cleveland Clinic, OH 44195, USA.
authors.forename: Jacob M
authors.initials: JM
authors.lastname: Haus
authors.forename: Thomas P J
authors.initials: TP
authors.lastname: Solomon
authors.forename: Lan
authors.initials: L
authors.lastname: Lu
authors.forename: John A
authors.initials: JA
authors.lastname: Jesberger
authors.forename: Hope
authors.initials: H
authors.lastname: Barkoukis
authors.forename: Chris A
authors.initials: CA
authors.lastname: Flask
authors.forename: John P
authors.initials: JP
authors.lastname: Kirwan
mesh_terms: D000368:Aged; D000375:Aging / Q000502:physiology; D001786:Blood Glucose / Q000378:metabolism; D001823:Body Composition; D004032:Diet; D015444:Exercise / Q000502:physiology*; D005081:Exercise Therapy; D005260:Female; D038321:Glycemic Index / Q000502:physiology*; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D007333:Insulin Resistance / Q000502:physiology*; D008019:Life Style; D015227:Lipid Peroxidation / Q000502:physiology; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000378:metabolism; D009765:Obesity / Q000378:metabolism / Q000503:physiopathology / Q000628:therapy*; D016896:Treatment Outcome
chemical_list: D001786:Blood Glucose; D007328:Insulin