Effects of 16-Week Consumption of Caffeinated and Decaffeinated Instant Coffee on Glucose Metabolism in a Randomized Controlled Trial

Abstract

Objective. Observational studies have shown a protective association between coffee consumption and type 2 diabetes mellitus whereas caffeine or caffeinated coffee acutely deteriorates glucose tolerance. We investigated the effects of chronic drinking of instant coffee on glucose and insulin concentrations during a 75 g oral glucose tolerance test. Methods. Overweight men with a mild-to-moderate elevation of fasting plasma glucose were randomly allocated to a 16-week intervention of consuming 5 cups of caffeinated (n = 17) or decaffeinated (n = 15) instant coffee per day or no coffee (n = 13). Results. The caffeinated coffee group showed statistically significant decreases in the 2-hour concentrations and the area under the curve of glucose while neither decaffeinated coffee nor coffee group showed such a change. Waist circumstance decreased in the caffeinated coffee group, increased in the decaffeinated coffee group, and did not change in the noncoffee group (P = 0.002). With adjustment for the change in waist circumference, caffeinated and decaffeinated coffee consumption were associated with a modest decrease in the postload glucose levels. Conclusion. Both caffeinated and decaffeinated coffee may be protective against deterioration of glucose tolerance.

Changes in coffee intake and subsequent risk of type 2 diabetes: three large cohorts of US men and women

“…Our data are largely consistent with findings from a 16-week randomized trial in which both caffeinated and decaffeinated coffee consumption were associated with modest decreases in post load glucose levels [22]. In an 8-week intervention study, coffee consumption increased adiponectin levels, an insulin sensitizing adipokine, but did not change measures of glycemia or insulin sensitivity [23].…”

Habitual coffee consumption and risk of type 2 diabetes, ischemic heart disease, depression and Alzheimer’s disease: a Mendelian randomization study

“…The associations of coffee with LDL-cholesterol and adiponectin are directionally consistent with those found in RCTs1112, but do not exclude no association. We also found no association of coffee with HbA1c, fasting glucose, fasting insulin, beta-cell function or insulin resistance, consistent with most121415 but not all16 RCTs. In addition, trends in coffee consumption do not coincide with the changing patterns of IHD or T2DM, for example IHD declined38 but DM rose39 in the United States where coffee consumption was stable in the past decade40.…”

“…Our study adds by replicating these findings in larger samples using more SNPs for coffee and showing coffee was also most likely unassociated with IHD and with glycemic traits, consistent with most121415 but not all16 RCTs. This study also adds by showing coffee most likely unrelated to depression and Alzheimer’s disease, although we cannot exclude the possibility that coffee increases the risk of Alzheimer’s disease.…”

“…A small RCT found that short-term coffee consumption increased adiponectin12, which may relate to lower CVD risk13. Several RCTs showed short-term coffee consumption had no effect on fasting glucose, fasting insulin or insulin resistance121415, although one RCT found it slightly increased glycosylated hemoglobin (HbA1c)16. The lack of evidence from long-term RCTs means that the effects of coffee on health are unclear, but are particularly important to establish in this window of opportunity before habitual coffee drinking extends to become the global norm.…”

Cardiometabolic effects of two coffee blends differing in content for major constituents in overweight adults: a randomized controlled trial

“…Published intervention trials include comparisons of coffee consumption versus abstention [9], caffeinated versus decaffeinated coffee [10,11] or pure caffeine [12], coffees differing in brewing type [13], or coffees enriched or reduced in special coffee constituents [14]. The roasting process has an important impact on the content of coffee constituents [15,16].…”