A randomised, placebo-controlled trial, published in the American Journal of Clinical Nutrition, showed no significant effect of coffee consumption on insulin sensitivity in those with type 2 diabetes.
Previous trials have had mixed results, with some suggesting coffee consumption improved insulin levels or insulin sensitivity, and reduced diabetes risk. However, past research has been hampered by small sample sizes, short follow-up periods and inadequate placebo controls.
In this study, 126 participants drank 4 cups of coffee or placebo per day for 24 weeks. While insulin resistance and associated mediators were not significantly affected, participants did lose a modest amount of fat mass.
The authors suggest that this loss of fat is the result of metabolic effects, as opposed to lifestyle changes. However, more research would be needed to confirm that this is the case. Furthermore, consumption of 4 cups of cofee per day may not be a practical means of weight loss, and may come with adverse effects. Finally, it should also be noted that the participants of the study were overweight and insulin resistant, and so may respond differently compared to healthy individuals.
The effect of coffee consumption on insulin sensitivity and other biological risk factors for type 2 diabetes: a randomized placebo-controlled trial: https://doi.org/10.1093/ajcn/nqz306