title: Effects of weight loss and physical activity on muscle lipid content and droplet size.
abstract: OBJECTIVE
  To address the potential effects of weight loss and physical activity (WL + Ex) on intramyocellular lipid (IMCL) and lipid droplet size in overweight and obese previously sedentary individuals.
  
  
  METHODS
  IMCL and lipid droplet size was determined in vastus lateralis, obtained by percutaneous biopsy, from 21 obese volunteers (9 men/12 women), using Oil Red O staining, along with succinate dehydrogenase histochemistry and mitochondrial immunohistochemistry as measures of skeletal muscle oxidative capacity. Insulin sensitivity (IS) was determined by glucose clamp.
  
  
  RESULTS
  A 4-month WL + Ex intervention resulted in approximately 10% WL and approximately 15% increase in maximal oxygen uptake, leading to a 46% increase in IS (all p < 0.01). IMCL did not significantly change (p = 0.36). However, the size of lipid droplets decreased after WL + Ex (p < 0.01), and this decrease in lipid droplet size correlated with increased IS (p < 0.01) and the amount of physical activity (p < 0.05). Succinate dehydrogenase activity and mitochondrial labeling increased significantly (p < 0.01), without a significant shift in fiber type distribution.
  
  
  CONCLUSIONS
  In summary, IMCL does not decrease in response to WL + Ex in obese, previously sedentary individuals, yet the lipid within muscle is dispersed into smaller droplets. This change in the size of lipid droplets, likely coupled with a concomitant increase in oxidative enzyme capacity, is correlated to improved IS.
authors.affiliation: Division of Endocrinology and Metabolism, Department of Medicine, University of Pittsburgh School of Medicine, Pennsyvania, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: He
authors.forename: Bret H
authors.initials: BH
authors.lastname: Goodpaster
authors.forename: David E
authors.initials: DE
authors.lastname: Kelley
mesh_terms: D000328:Adult; D001706:Biopsy; D001823:Body Composition; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism / Q000473:pathology; D015444:Exercise; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D042541:Intracellular Space / Q000737:chemistry; D008055:Lipids / Q000032:analysis* / Q000737:chemistry*; D008297:Male; D018613:Microscopy, Confocal; D008931:Mitochondria, Muscle / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000737:chemistry* / Q000201:enzymology / Q000648:ultrastructure; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D010316:Particle Size; D010809:Physical Fitness; D013385:Succinate Dehydrogenase / Q000378:metabolism; D015431:Weight Loss
chemical_list: D008055:Lipids; D013385:Succinate Dehydrogenase