Distinct patterns of fat metabolism in skeletal muscle of normal-weight, overweight, and obese humans

1 Center for Advanced Imaging and Department of Radiology, 2 Center for Interdisciplinary Research in Cardiovascular Sciences, 3 Department of Community Medicine, 4 Department of Physiology and Pharmacology, 6 Departments of Biochemistry, Microbiology, and Immunology, and 8 Department of Exercise Physiology, West Virginia University, Morgantown, West Virginia; 5 Department of Radiology, University of California, Los Angeles, California; and 7 Magnetic Resonance Imaging and Spectroscopy Section, National Institute on Aging, National Institutes of Health, Baltimore, Maryland Submitted 17 April 2008 ; accepted in final form 28 July 2008 The link between body weight, lipid metabolism, and health risks is poorly understood and difficult to study. Magnetic resonance spectroscopy (MRS) permits noninvasive investigation of lipid metabolism. We extended existing two-dimensional MRS techniques to permit quantification of intra- and extramyocellular lipid (IMCL and EMCL, respectively) compartments and their degree of unsaturation in human subjects and correlated these results with body mass index (BMI). Using muscle creatine for normalization, we observed a statistically significant ( P < 0.01) increase in the IMCL-to-creatine ratio with BMI ( n = 8 subjects per group): 5.9 ± 1.7 at BMI < 25, 10.9 ± 1.82 at 25 < BMI < 30, and 13.1 ± 0.87 at BMI > 30. Similarly, the degree of IMCL unsaturation decreased significantly ( P < 0.01) with BMI: 1.51 ± 0.08 at BMI < 25, 1.30 ± 0.11 at 25 < BMI < 30, and 0.90 ± 0.14 at BMI > 30. We conclude that important aspects of lipid metabolism can be evaluated by two-dimensional MRS and propose that degree of unsaturation measured noninvasively may serve as a biomarker for lipid metabolic defects associated with obesity. magnetic resonance spectroscopy; lipid unsaturation; intramyocellular lipid; extramyocellular lipid Address for reprint requests and other correspondence: S. S. Velan, Center for Advanced Imaging and Radiology, West Virginia Univ., Morgantown, WV 26506 (e-mail: svelan{at}hsc.wvu.edu )