The effects of coffee consumption on insulin sensitivity and other risk factors for type 2 diabetes

Abstract

Background: In observational studies, coffee consumption has been consistently associated with a lower risk of type 2 diabetes mellitus. Trials examining the effect of coffee consumption on glucose metabolism have been limited by the use of surrogate insulin sensitivity indices, small sample sizes, lack of blinding, and short follow-up duration. We aimed to overcome these limitations in a randomized placebo-controlled trial examining the effects of coffee consumption on insulin sensitivity. Methodology: We conducted a 24-week randomized placebo-controlled trial in 126 overweight, insulin-resistant (HOMA-IR ≥ 1.30), Chinese, Malay and Asian-Indian males and females aged 35-69 years. Participants were randomly assigned to receive 4 cups of instant regular coffee (n=62) or 4 cups of a coffee-like placebo beverage (n=64) per day. The primary outcome was bodyweight-standardized M-value (Mbw) assessed with a hyperinsulinemic euglycemic clamp. Secondary outcomes included other clamp-based insulin sensitivity measures, biological mediators of insulin sensitivity, and measures of fasting glucose metabolism, body weight and composition. Results: Coffee consumption did not significantly change insulin sensitivity as compared with placebo [% mean difference in Mbw: 0.3% (95% CI:-12.0% to 14.2%), P=0.97]. Furthermore, no significant differences in fasting plasma glucose [3.0% (-1.1% to 7.3%), P=0.16] or biological mediators of insulin resistance, such as plasma adiponectin [1.5% (-3.4% to 6.6%), P=0.55], were observed between coffee and placebo groups after 24 weeks of intervention. Coffee consumption led to a loss of body weight as compared with placebo [-1.2% (-2.3% to-0.1%), P=0.03] resulting from a decrease in fat mass [-3.7% (-7.1% to-0.2%), P=0.04]. Conclusions: Consuming 4 cups per day of caffeinated coffee for 24 weeks had no significant effect on insulin sensitivity or biological mediators of insulin resistance. Coffee consumption led to a modest decrease in body fat as compared with coffee abstinence.