title: Effects of weight loss and exercise on insulin resistance, and intramyocellular triacylglycerol, diacylglycerol and ceramide.
abstract: OBJECTIVE
  Intramyocellular lipids, including diacylglycerol (DAG) and ceramides, have been linked to insulin resistance. This randomised repeated-measures study examined the effects of diet-induced weight loss (DIWL) and aerobic exercise (EX) on insulin sensitivity and intramyocellular triacylglycerol (IMTG), DAG and ceramide.
  
  
  METHODS
  Sixteen overweight to obese adults (BMI 30.6 ± 0.8; 67.2 ± 4.0 years of age) with either impaired fasting glucose, or impaired glucose tolerance completed one of two lifestyle interventions: DIWL (n = 8) or EX (n = 8). Insulin sensitivity was determined using hyperinsulinaemic-euglycaemic clamps. Intramyocellular lipids were measured in muscle biopsies using histochemistry and tandem mass spectrometry.
  
  
  RESULTS
  Insulin sensitivity was improved with DIWL (20.6 ± 4.7%) and EX (19.2 ± 12.9%). Body weight and body fat were decreased by both interventions, with greater decreases in DIWL compared with EX. Muscle glycogen, IMTG content and oxidative capacity were all significantly (p < 0.05) decreased with DIWL and increased with EX. There were decreases in DAG with DIWL (-12.4 ± 14.6%) and EX (-40.9 ± 12.0%). Ceramide decreased with EX (-33.7 ± 11.2%), but not with DIWL. Dihydroceramide was decreased with both interventions. Sphingosine was decreased only with EX. Changes in total DAG, total ceramides and other sphingolipids did not correlate with changes in glucose disposal. Stearoyl-coenzyme A desaturase 1 (SCD1) content was decreased with DIWL (-19.5 ± 8.5%, p < 0.05), but increased with EX (19.6 ± 7.4%, p < 0.05). Diacylglycerol acyltransferase 1 (DGAT1) was unchanged with the interventions.
  
  
  CONCLUSIONS
  Diet-induced weight loss and exercise training both improved insulin resistance and decreased DAG, while only exercise decreased ceramides, despite the interventions having different effects on IMTG. These alterations may be mediated through differential changes in skeletal muscle capacity for oxidation and triacylglycerol synthesis.
  
  
  BACKGROUND
  ClinicalTrials.gov NCT00766298.
authors.affiliation: Division of Endocrinology and Metabolism, Department of Medicine, University of Pittsburgh School of Medicine, University of Pittsburgh, 3459 Fifth Avenue, MUH N807, Pittsburgh, PA 15213, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Dubé
authors.forename: F
authors.initials: F
authors.lastname: Amati
authors.forename: F G S
authors.initials: FG
authors.lastname: Toledo
authors.forename: M
authors.initials: M
authors.lastname: Stefanovic-Racic
authors.forename: A
authors.initials: A
authors.lastname: Rossi
authors.forename: P
authors.initials: P
authors.lastname: Coen
authors.forename: B H
authors.initials: BH
authors.lastname: Goodpaster
mesh_terms: D000368:Aged; D001823:Body Composition; D002518:Ceramides / Q000378:metabolism*; D004038:Diet, Reducing; D004075:Diglycerides / Q000378:metabolism*; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D007333:Insulin Resistance / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000378:metabolism; D014280:Triglycerides / Q000378:metabolism*; D015431:Weight Loss / Q000502:physiology*
chemical_list: C011439:1,2-diacylglycerol; D002518:Ceramides; D004075:Diglycerides; D014280:Triglycerides