Relationships between fat deposition in the liver and skeletal muscle and insulin sensitivity in Japanese individuals: a pilot study

Eiichi Yoshimura^1,2, Hideaki Kumahara³, Takuro Tobina⁴, Sakiko Matono¹, Akira Kiyonaga⁴, Miyuki Kimura⁵, Hiroshi Tsukikawa⁶, Shinya Kono⁶, Takashi Etou⁵, Shin Irie⁵, Keizo Anzai⁷, Hiroaki Tanaka^4
1Graduate School of Sports and Health Science, Fukuoka University, Fukuoka, Japan; ²Faculty of Medicine, Fukuoka University, Fukuoka, Japan; ³Faculty of Nutrition Sciences, Nakamura Gakuen University, Fukuoka, Japan; ⁴Faculty of Sports and Health Science, Fukuoka University, Fukuoka, Japan; ⁵Kyushu Clinical Pharmacology Research Clinic, Fukuoka, Japan; ⁶PS Clinic, Fukuoka, Japan; ⁷Saga University Hospital, Saga, Japan

Purpose: To evaluate the relationships between insulin sensitivity (IS), body fat accumulation, and aerobic capacity in middle- to older-aged Japanese participants with visceral adiposity.
Participants and methods: Aerobic capacity was measured during an incremental ramp exercise test. Computed tomography was used to measure visceral (VFA) and subcutaneous (SFA) fat area, the fat in liver-to-spleen ratio (L/S), and low-density skeletal muscle area (LDMA). IS was assessed using euglycemic-hyperinsulinemic clamps.
Results: A total of 11 males and 9 females, age 58 ± 9 years (mean ± standard deviation), body mass index 29 ± 4.1 kg/m², and VFA 190 ± 53 cm² participated in this study. In unadjusted models, VFA, LDMA, and L/S were significantly correlated with IS, which remained in adjusted models for LDMA and L/S, but not for VFA. In multiple stepwise regression analysis including sex, age, body fat, VFA, SFA, alcohol consumption, and aerobic capacity (oxygen uptake at the lactate threshold), L/S, and LDMA accounted for 70% of the total variance in IS. Percentage body fat and SFA, but not VFA, were significantly correlated with high molecular-weight adiponectin levels (r = 0.58, P < 0.01 and r = 0.54, P < 0.05, respectively). IS and L/S were significantly and negatively correlated with tumor necrosis factor-α (r = -0.67 and -0.63, respectively; both P < 0.01) and plasminogen activator inhibitor-1 (r = -0.58, P < 0.01 and -0.52, P < 0.05, respectively), whereas LDMA was not.
Conclusion: These findings indicate that ectopic fat deposition in the liver and skeletal muscle may be associated with peripheral IS independently of body fat accumulation and aerobic capacity in middle- to older-aged Japanese individuals with visceral adiposity. Because of the small sample size, additional larger studies are needed to provide further insight into these preliminary findings.

Keywords: aerobic capacity, fat in liver, lipid-rich skeletal muscle, visceral fat, subcutaneous fat, peripheral insulin sensitivity