Caffeine and Oral Glucose Tolerance Test

Caffeine is a common biologically active food component that has been recently implicated in acute insulin resistance.

Researchers at the University of Guelph, Ontario, Canada, investigated the effect of caffeine on glucose tolerance and insulin sensitivity responses during an oral glucose tolerance test (OGTT) in obese men with type 2 diabetes. Two trials were conducted in a randomized double-blind study. Both trials were conducted after withdrawal from caffeine, alcohol, exercise, and hypoglycemic agents for 48 hours and an overnight fast. The subjects either ingested a caffeine capsule or a placebo and 1 hour later the men began an OGTT.

Caffeine increased serum insulin, proinsulin, and C-peptide concentrations during OGTT relative to the placebo. Insulin levels were 25% greater after the caffeine trial than after placebo ingestion. Despite this, blood glucose concentration was also increased in the caffeine trial. After caffeine, blood glucose remained elevated 3 hours after the glucose ingestion.

Researchers concluded that “despite elevated and prolonged proinsulin, C-peptide and insulin responses after caffeine ingestion, blood glucose was also increased, suggesting an acute caffeine-induced impairment in blood glucose management in obese men with type 2 diabetes.”