title: Caffeine ingestion increases the insulin response to an oral-glucose-tolerance test in obese men before and after weight loss.
abstract: BACKGROUND
  Caffeine ingestion decreases the insulin sensitivity index (ISI) for an oral-glucose-tolerance test (OGTT) and decreases insulin-induced glucose disposal in lean male subjects during a hyperinsulinemic clamp.
  
  
  OBJECTIVE
  We examined the effects of caffeine ingestion on insulin and glucose homeostasis in obese men before and after a nutrition and exercise intervention.
  
  
  METHODS
  Nine sedentary, obese [body mass index (in kg/m(2)): 34.0 +/- 1.0] men who had refrained from exercise and caffeine ingestion for 48 h underwent 2 oral-glucose-tolerance tests (OGTTs). The subjects randomly received caffeine (5 mg/kg) or placebo 1 h before each OGTT. After a 12-wk nutrition and exercise intervention, during which time the subjects avoided dietary caffeine, the OGTTs were repeated.
  
  
  RESULTS
  The intervention resulted in decreases (P < or = 0.05) in body weight (8.5 +/- 1.5 kg), percentage body fat (2.8 +/- 0.7%), and fasting glucose, insulin, and proinsulin concentrations and increases in the ISI for the placebo OGTT (P < or = 0.05). Caffeine caused a greater (P < or = 0.05) OGTT insulin response and a lower (P < or = 0.05) ISI both before and after weight loss. The proinsulin-insulin ratio indicated that neither weight loss nor caffeine affected the nature of the beta cell secretion of insulin.
  
  
  CONCLUSIONS
  A nutrition and exercise intervention improved, whereas caffeine ingestion impaired, insulin-glucose homeostasis in obese men. The results are consistent with previous findings that caffeine ingestion contributes to insulin resistance.
authors.affiliation: Department of Human Biology and Nutritional Sciences, University of Guelph, Ontario, Canada.
authors.forename: Heather J
authors.initials: HJ
authors.lastname: Petrie
authors.forename: Sara E
authors.initials: SE
authors.lastname: Chown
authors.forename: Laura M
authors.initials: LM
authors.lastname: Belfie
authors.forename: Alison M
authors.initials: AM
authors.lastname: Duncan
authors.forename: Drew H
authors.initials: DH
authors.lastname: McLaren
authors.forename: Julie A
authors.initials: JA
authors.lastname: Conquer
authors.forename: Terry E
authors.initials: TE
authors.lastname: Graham
mesh_terms: D000284:Administration, Oral; D000328:Adult; D019540:Area Under Curve; D001786:Blood Glucose / Q000378:metabolism*; D002096:C-Peptide / Q000378:metabolism; D002110:Caffeine / Q000008:administration & dosage / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000008:administration & dosage / Q000494:pharmacology*; D004038:Diet, Reducing; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology; D015309:Glucose Clamp Technique; D005951:Glucose Tolerance Test; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D007333:Insulin Resistance; D019344:Lactic Acid / Q000097:blood; D008297:Male; D009765:Obesity / Q000378:metabolism* / Q000628:therapy; D011384:Proinsulin / Q000097:blood; D015431:Weight Loss / Q000502:physiology*; D014970:Xanthines / Q000652:urine
chemical_list: D001786:Blood Glucose; D002096:C-Peptide; D000697:Central Nervous System Stimulants; D007328:Insulin; D014970:Xanthines; C008514:methylxanthine; D019344:Lactic Acid; D002110:Caffeine; D011384:Proinsulin