Caffeine ingestion increases the insulin response to an oral-glucose-tolerance test in obese men before and after weight loss

Am J Clin Nutr. 2004 Jul;80(1):22-8. doi: 10.1093/ajcn/80.1.22.


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.

Design: 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.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Oral
  • Adult
  • Area Under Curve
  • Blood Glucose / metabolism*
  • C-Peptide / metabolism
  • Caffeine / administration & dosage
  • Caffeine / pharmacology*
  • Central Nervous System Stimulants / administration & dosage
  • Central Nervous System Stimulants / pharmacology*
  • Diet, Reducing
  • Double-Blind Method
  • Exercise / physiology
  • Glucose Clamp Technique
  • Glucose Tolerance Test
  • Humans
  • Insulin / metabolism*
  • Insulin Resistance
  • Lactic Acid / blood
  • Male
  • Obesity / metabolism*
  • Obesity / therapy
  • Proinsulin / blood
  • Weight Loss / physiology*
  • Xanthines / urine


  • Blood Glucose
  • C-Peptide
  • Central Nervous System Stimulants
  • Insulin
  • Xanthines
  • methylxanthine
  • Lactic Acid
  • Caffeine
  • Proinsulin