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Journal of Nutrition and Metabolism
Volume 2012, Article ID 207426, 9 pages
http://dx.doi.org/10.1155/2012/207426
Research Article

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

1Department of Geriatric Medicine, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan
2Department of Preventive Medicine, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan
3Department of Clinical Pharmacology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka 812-8582, Japan
4Department of Medicine and Bioregulatory Science, Graduate School of Medical Sciences, Higashi-ku, Fukuoka 812-8582, Japan

Received 4 April 2012; Revised 9 October 2012; Accepted 9 October 2012

Academic Editor: Cindy Davis

Copyright © 2012 Keizo Ohnaka et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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 ( ) or decaffeinated ( ) instant coffee per day or no coffee ( ). 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 ( ). 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.