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Am J Clin Nutr. 2019 Dec 31. pii: nqz306. doi: 10.1093/ajcn/nqz306. [Epub ahead of print]

The effect of coffee consumption on insulin sensitivity and other biological risk factors for type 2 diabetes: a randomized placebo-controlled trial.

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NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore (NUS), Singapore.
A*STAR Graduate Academy, Agency for Science, Technology and Research (A*STAR), Singapore.
Saw Swee Hock School of Public Health, National University of Singapore, Singapore.
Department of Nutrition, Harvard T.H. Chan School of Public Health, Harvard University, Boston, MA, USA.
Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
Division of Endocrinology, National University Hospital, National University Health System, Singapore.
Investigational Medicine Unit, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
Clinical Development Unit, Nestlé Research, Lausanne, Switzerland.
Nestlé Institute of Health Sciences, Nestlé Research, Lausanne, Switzerland.



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 limitations of previously conducted coffee trials in a randomized placebo-controlled trial of the effect of coffee consumption on insulin sensitivity.


We conducted a 24-wk randomized placebo-controlled trial in 126 overweight, non-insulin sensitive (HOMA-IR ≥1.30), Chinese, Malay, and Asian-Indian males and females aged 35-69 y. 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 the amount of glucose metabolized per kilogram of body weight per minute (Mbw) assessed during steady-state conditions 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.


Coffee consumption did not significantly change insulin sensitivity compared with placebo (percentage mean difference in Mbw = 4.0%; 95% CI: -8.3, 18.0%; P = 0.53). Furthermore, no significant differences in fasting plasma glucose (2.9%; 95% CI: -0.4, 6.3%; P = 0.09) or biological mediators of insulin resistance, such as plasma adiponectin (2.3%; 95% CI: -1.4, 6.2%; P = 0.22), were observed between coffee and placebo groups over 24 wk of intervention. Participants in the coffee arm experienced a loss of fat mass (FM) (-3.7%; 95% CI: -6.3, -1.1%; P = 0.006) and reduction in urinary creatinine concentrations (-21.2%; 95% CI: -31.4, -9.5%; P = 0.001) compared with participants in the placebo arm over 24 wk of intervention.


Consuming 4 cups/d of caffeinated coffee for 24 wk had no significant effect on insulin sensitivity or biological mediators of insulin resistance but was associated with a modest loss of FM and reduction in urinary creatinine concentrations.This trial was registered at as NCT01738399. Registered on November 28, 2012. Trial sponsor: Nestlé Research, Lausanne, Switzerland. Trial site: National University of Singapore.


adult-onset diabetes mellitus; coffee; humans; hyperinsulinemic euglycemic clamp; insulin resistance; insulin sensitivity; metabolic health; type 2 diabetes


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