Intramuscular lipid content is increased in obesity and decreased by weight loss

The triglyceride content of skeletal muscle samples determined by lipid ext raction correlates with the severity of insulin-resistant glucose metabolis m in muscle. To determine whether this reflects increased triglyceride with in muscle fibers and to test the hypothesis that the lipid content in muscl e fibers is increased in obesity, the present study was undertaken using qu antitative histochemistry of Oil Red O staining of vastus lateralis muscle. A percutaneous muscle biopsy was performed in 9 lean subjects, 15 obese su bjects without type 2 diabetes mellitus (DM), and 10 obese subjects with ty pe 2 DM (body mass index [BMI], 23.4 +/- 1.0, 33.6 +/- 0.6, and 36.0 =/- 1. 1 kg . m(-2) for lean, obese, and DM, respectively). Eight obese and 7 DM s ubjects had a weight loss and reassessment of muscle lipid content. Transve rse muscle cryosections were examined by light microscopy with quantitative image analysis (grayscale images obtained by analog to digital conversion) to determine a lipid accumulation index (LAI) based on the percentage of c ross-sectional fiber area occupied by lipid droplets. Muscle fiber lipid co ntent was greater in obese individuals with DM than in lean individuals (3. 62% +/- 0.65% v 1.42% +/- 0.28%, P <.05) but was not different in obese ind ividuals without DM (2.53% +/- 0.41%). Weight loss reduced the LAI from 3.4 3% +/- 0.53% to 2.35% +/- 0.31%. In summary, lipid accumulation within musc le fibers is significantly increased in obesity and is reduced by weight lo ss. This provides important information regarding the accumulation and dist ribution of skeletal muscle triglyceride in type 2 DM and obesity. Copyrigh t (C) 2000 by W.B. Saunders Company.