Decaffeinated Coffee and Glucose Metabolism in Young Men

The epidemiological association between coffee drinking and decreased risk of Type 2 diabetes is strong. However, caffeinated coffee acutely impairs glucose metabolism. Researchers assessed acute effects of decaffeinated coffee on glucose and insulin levels.

This was a randomized, cross-over, placebo-controlled trial of the effects of decaffeinated coffee, caffeinated coffee, and caffeine on glucose, insulin, and glucose-dependent insulinotropic polypeptide (GIP) levels during a 2-h oral glucose tolerance test (OGTT) in 11 young men.

Nineteen of 22 epidemiological studies concluded that long-term consumption of coffee, both caffeinated and decaffeinated, can reduce the risk of Type 2 diabetes, but several investigators have warned that the caffeine in caffeinated coffee can impair glucose metabolism. While decaffeinated coffee contains very little caffeine and may safely protect against diabetes, there have been conflicting reports on decaffeinated coffee's acute effects on glucose metabolism. Our objective was to assess whether ground decaffeinated coffee enhances glucose metabolism and whether glucose-dependent insulinotropic polypeptide (GIP), an incretin hormone that stimulates insulin secretion, plays a causal role.

Decaffeinated coffee acutely impaired glucose metabolism in healthy young men. Within the first 60 min of the OGTT, both glucose and insulin were significantly higher after decaffeinated coffee than after placebo. During the whole OGTT, insulin AUC was significantly higher for decaffeinated coffee than placebo. Decaffeinated coffee did not impair glucose metabolism as severely as caffeine. During the whole OGTT, decaffeinated coffee yielded lower glucose AUC and higher ISI than caffeine. Our findings require confirmation in future studies. However, they do suggest that caution is needed in the quest to harness coffee's potential to reduce the risk of diabetes, demonstrated in epidemiological studies.

The results showed that, within the first hour of the OGTT, glucose and insulin were higher for decaffeinated coffee than for placebo (P < 0.05). During the whole OGTT, decaffeinated coffee yielded higher insulin than placebo and lower glucose and a higher insulin sensitivity index than caffeine. Changes in GIP could not explain any beverage effects on glucose and insulin.

Battram et al. found an acute enhancement of glucose metabolism by ground decaffeinated coffee, and Johnston et al Thom, and van Dijk et al. found no acute effect on glucose metabolism by instant decaffeinated coffee. It is possible that the decaffeinated coffee used had a higher concentration of caffeine than the decaffeinated coffees of these investigators, or that it had lower concentrations of non-caffeine compounds, which acutely enhance glucose metabolism. It seems unlikely that GIP played a role in the observed beverage effects. For example, 60 min after beverage ingestion, decaffeinated coffee yielded significantly lower GIP than placebo and caffeine but no significant changes in insulin or glucose.

In conclusion, the human trial appears to be the first to find that decaffeinated coffee can acutely impair glucose metabolism, but less than caffeine, in healthy young men.

Diabetes Care. 2010;33(2):278-280