Centre de recherche de l'Institut universitaire de cardiologie et de pneumologie de Québec - Université Laval, Québec, QC, Canada; Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, QC, Canada.
Centre de recherche de l'Institut universitaire de cardiologie et de pneumologie de Québec - Université Laval, Québec, QC, Canada.
Metabolism. 2018 Aug;85:205-212. doi: 10.1016/j.metabol.2018.04.003. Epub 2018 Apr 12.
BACKGROUND/OBJECTIVES: Thigh muscle attenuation measured by computed tomography (CT) has been shown to be a reliable and useful index of skeletal muscle fat infiltration. Thigh muscle fat content assessed by CT has been linked to obesity and type 2 diabetes and is a correlate of insulin resistance in sedentary individuals. However, as measurement of mid-thigh fat content requires the assessment of another region of interest beyond the usual abdominal scan required to measure levels of visceral and subcutaneous abdominal adipose tissue, this study aimed at testing the hypothesis that skeletal muscle fat measured from a single abdominal scan (L-L) would also provide information relevant to the estimation of muscle fat infiltration as it relates to cardiometabolic risk.
Abdominal (L-L) and mid-thigh CT scans were performed in a sample of 221 sedentary men covering a wide range of adiposity values. Trunk muscles on the L-L scan were classified into 2 groups: 1) psoas and 2) core muscles. The two scans were segmented to calculate muscle areas, mean attenuation values as well as low-attenuation muscle (LAM) areas, the latter being considered as an index of skeletal muscle fat infiltration. Body mass index (BMI), body composition and waist circumference were assessed and a 75 g oral glucose tolerance test (OGTT) was performed.
Mid-thigh, psoas and core LAM areas were all significantly associated with body composition indices (0.46 ≤ r ≤ 0.71, p < 0.0001) whereas trunk muscle indices were more strongly associated with visceral adiposity and waist circumference (0.54 ≤ r ≤ 0.79, p < 0.0001) than were mid-thigh muscle variables (0.44 ≤ r ≤ 0.62, p < 0.0001). Mid-thigh LAM area as well as psoas and core LAM areas were significantly associated with fasting glucose, 2-h plasma glucose levels, the glucose area under the curve and with the HOMA-IR index (mid-thigh LAM area: 0.18 ≤ r ≤ 0.25, p < 0.01; psoas LAM area: 0.27 ≤ r ≤ 0.33, p < 0.0001; core LAM area: 0.24 ≤ r ≤ 0.34, p < 0.01). Multivariable stepwise regression analyses revealed that the associations between trunk muscle indices and glucose tolerance/insulin resistance were no longer significant after controlling for visceral adiposity measured at L-L.
Our results suggest that CT-imaging derived indices of trunk muscle quality are related to glucose tolerance and visceral adiposity. However, the relationship between skeletal muscle fat and insulin resistance appears to be largely mediated by the concomitant variation in visceral adiposity. Finally, our results suggest that a single CT scan performed at L-L is adequate to assess skeletal muscle fat content related to cardiometabolic risk.
背景/目的：通过计算机断层扫描（CT）测量的大腿肌肉衰减已被证明是骨骼肌肉脂肪浸润的可靠且有用的指标。通过 CT 评估的大腿肌肉脂肪含量与肥胖和 2 型糖尿病有关，并且与久坐个体的胰岛素抵抗相关。然而，由于测量中大腿脂肪含量需要评估腹部扫描以外的另一个感兴趣区域，该区域除了测量内脏和皮下腹部脂肪组织水平之外，还需要评估腹部扫描（L-L）中的中大腿脂肪含量，因此本研究旨在测试以下假设：从单次腹部扫描（L-L）测量的骨骼肌脂肪也将提供与肌肉脂肪浸润相关的信息，因为它与代谢风险有关。
对 221 名久坐的男性进行了腹部（L-L）和中大腿 CT 扫描，这些男性的体脂率值差异很大。L-L 扫描上的躯干肌肉分为 2 组：1）腰大肌和 2）核心肌肉。对这两个扫描进行分割以计算肌肉面积，平均衰减值以及低衰减肌肉（LAM）面积，后者被认为是骨骼肌肉脂肪浸润的指标。评估了体重指数（BMI）、身体成分和腰围，并进行了 75g 口服葡萄糖耐量试验（OGTT）。
中大腿、腰大肌和核心 LAM 区域均与身体成分指数显著相关（0.46≤r≤0.71，p<0.0001），而躯干肌肉指数与内脏脂肪和腰围的相关性更强（0.54≤r≤0.79，p<0.0001）比中大腿肌肉变量（0.44≤r≤0.62，p<0.0001）。中大腿 LAM 区域以及腰大肌和核心 LAM 区域与空腹血糖、2 小时血浆葡萄糖水平、血糖曲线下面积和 HOMA-IR 指数显著相关（中大腿 LAM 区域：0.18≤r≤0.25，p<0.01；腰大肌 LAM 区域：0.27≤r≤0.33，p<0.0001；核心 LAM 区域：0.24≤r≤0.34，p<0.01）。多元逐步回归分析显示，在控制 L-L 处测量的内脏脂肪后，躯干肌肉指数与葡萄糖耐量/胰岛素抵抗之间的关联不再显著。
我们的结果表明，源自 CT 成像的躯干肌肉质量指数与葡萄糖耐量和内脏脂肪有关。然而，骨骼肌脂肪与胰岛素抵抗之间的关系似乎主要是由内脏脂肪的同时变化介导的。最后，我们的结果表明，在 L-L 处进行单次 CT 扫描足以评估与代谢风险相关的骨骼肌脂肪含量。
