Determinants of intramyocellular lipid accumulation after dietary fat loading in non-obese men

Abstract

Aims/Introduction: Accumulation of intramyocellular lipid (IMCL) is associated with insulin resistance. However, the factors affecting the change in IMCL remain to be elucidated. The aim of the present study was to determine the factors that influence the change in IMCL level after high-fat loading.

Materials and methods: The study subjects were 37 non-obese men. Each subject consumed a high-fat diet for 3 days after a normal-fat diet for 3 days. After each diet program, IMCL levels in the tibialis anterior (TA-IMCL) and soleus (SOL-IMCL) were measured by proton magnetic resonance spectroscopy. Glucose infusion rate (GIR) was evaluated by euglycemic hyperinsulinemic clamp as an index of peripheral insulin sensitivity.

Results: The high-fat diet significantly increased TA-IMCL and SOL-IMCL by ∼30 and ∼20%, respectively (P < 0.05), whereas it did not significantly alter GIR. The increase in SOL-IMCL, but not in TA-IMCL, negatively correlated with serum high molecular weight (HMW)-adiponectin (r = -0.36, P < 0.05) and HMW-/total-adiponectin ratio (r = -0.46, P < 0.05). Although high-fat diet-related changes in SOL-IMCL showed high inter-individual variations, in subjects doing exercise, changes in SOL-IMCL (r = 0.55, P < 0.05) and TA-IMCL (r = 0.61, P < 0.05) positively correlated with daily physical activity level. In contrast, in sedentary subjects, changes in SOL-IMCL (r = -0.50, P < 0.01) and TA-IMCL (r = -0.48, P < 0.05) negatively correlated with daily physical activity.

Conclusions: HMW-adiponectin and daily physical activity are determinants of IMCL accumulation by a high-fat diet. Intriguingly, the effect of daily physical activity on the change in IMCL depends on the level of regular exercise. (J Diabetes Invest,doi: 10.1111/j.2040-1124.2010.00091.x, 2011).

Keywords: Adiponectin; Intramyocellular lipid; Physical activity.

Figure 1

Changes in intramyocellular lipid (IMCL) and glucose infusion rate (GIR) during euglycemic hyperinsulinemic glucose clamp study in a high‐fat diet. (a) IMCL level in the tibialis anterior muscle (TA) after a normal‐fat and high‐fat diet. Close‐up figure is also shown. (b) IMCL level in soleus muscle (SOL) after normal fat and high‐fat diet. (c) GIR after normal fat and high‐fat diet.

Figure 2

Determinants of percentage changes in intramyocellular lipid (IMCL) in soleus muscle (SOL) in a high‐fat diet and percentage change in IMCL in tibialis anterior muscle (TA) in a high‐fat diet. (a) Correlation between percentage change in IMCL levels in SOL and basal SOL‐IMCL levels. (b) Correlation between percentage change in IMCL levels and log‐transformed high‐molecular weight (HMW)‐adiponectin. (c) Correlation between percentage change in IMCL levels in SOL and HMW‐adiponectin/total‐adiponectin ratio. (d) Correlation between percentage change in IMCL levels in TA and basal TA‐IMCL levels.

Figure 3

Relationship between daily physical activity and percentage change in intramyocellular lipid (IMCL) levels in regular exercise (RE) and non‐regular exercise group (NRE) groups. (a,b) Correlation between daily physical activity and percentage change in IMCL levels in (a) tibialis anterior muscle (TA) and (b) soleus muscle (SOL) in NRE group. (c,d) Correlation between daily physical activity and percentage change in IMCL levels in (c) TA and (d) SOL in the RE group.

Figure 4

Relationship between daily physical activity and percentage change in intramyocellular lipid (IMCL) levels in higher and lower maximum oxygen uptake groups. The correlation between daily physical activity and percentage change in IMCL levels in (a) tibialis anterior muscle (TA) and (b) soleus muscle (SOL) in the low maximum oxygen uptake (<50 mL/kg/min, n = 16) group. The correlation between daily physical activity and percentage change in IMCL levels in (c) TA and (d) SOL in the high maximum oxygen uptake (≥50 mL/kg/min, n = 11) group.