Getting the skinny on scientific studies can be a tricky business. On one hand, coffee is suspected of sabotaging weight-loss efforts by lowering your insulin sensitivity, while on the other hand coffee-drinking is associated with lower blood-glucose and insulin levels, which leads to a decreased risk for diabetes and obesity. As of 2011, the clinical implications of coffee-drinking and its effects on insulin and weight-management remain murky.
Understanding Insulin
Insulin is intimately related to body fat. Insulin transports glucose, or sugar, to your cells so they can use it for energy. Insulin also helps store fat. When you have more glucose in your bloodstream than the cells in your body need, insulin takes the extra amount and transports it into fat storage, which returns your blood-sugar levels to normal. When your insulin levels are consistently high, more fat gets stored in your body.
Lower Insulin Sensitivity Evidence
Drinking large amounts of coffee can lower insulin sensitivity and raise blood-glucose concentrations, at least in the short term, according to a December 2004 “Diabetes Care” study. Lower insulin sensitivity, or insulin resistance, means your cells absorb less glucose from your bloodstream and your body releases more insulin to do its job with glucose. This raises risk for type 2 diabetes and obesity. Improving insulin sensitivity has the opposite effect. The “Diabetes Care” study examined the effects of high coffee consumption over a four-week time frame. The results are at odds with the inverse association between habitual coffee consumption and type 2 diabetes risk, so lead study author Rob M. van Dam recommends long-term research on coffee consumption that includes detailed measures of glucose metabolism and insulin sensitivity.
Improved Insulin Evidence
A January 2006 “Hormone and Metabolic Research” study reached a different conclusion. In this study, Finish researchers measured blood-glucose and insulin levels after fasting and two hours after taking an oral glucose tolerance test among 2,434 coffee drinkers. The researchers made adjustments for factors such as smoking, age, body mass index, blood pressure, alcohol consumption, tea consumption and physical activity related to occupation and leisure time, notes lead study author S. Bidel. The study concludes that coffee shows positive effects on numerous glycemia markers. Coffee drinkers had better fasting glucose, two-hour blood-glucose and fasting insulin levels. Coffee drinkers also were less likely to have impaired glucose regulation and too-high insulin levels, according to Bidel.
Coffee Substance Effects
Researchers are still working to understand coffee, the substances it contains and their effects on insulin. Coffee contains thousands of compounds in addition to caffeine. A December 2008 “Applied Physiology, Nutrition and Metabolism” study notes that correlations between lower type 2 diabetes risk and higher coffee consumption are seen with both caffeinated and decaffeinated coffee, and exist regardless of geography, gender or brewing method. This correlation also exists despite clear scientific evidence that caffeine causes acute post-meal hyperglycemia, meaning high blood sugar, and reduced insulin sensitivity, notes lead study author J.M. Tunnicliffe. Coffee contains numerous substances that might be responsible for its effects on blood-sugar and insulin, according to Tunnicliffe. When coffee is roasted, for example, an antioxidant it contains called chlorogenic acid is transformed into quinides, which are compounds that alter your blood-glucose levels. Coffee also may act as a prebiotic and alter the flora in your gut, which affects digestion. Coffee also might change levels of peptides in your gut that are involved in the regulation insulin secretion and of satiety.
References
- “The Diabetes Coach Approach Workbook”; Janet Sanders; 2009
- “Diabetes Care”; Effects of Coffee Consumption on Fasting Blood Glucose and Insulin Concentration; Rob M. van Dam , et. al; December 2004
- “Hormone and Metabolic Research”; Effects of Coffee Consumption on Glucose Tolerance, Serum Glucose and Insulin Levels; S. Bidel, et. al; January 2006
- “Applied Physiology, Nutrition and Metabolism”; Coffee, Glucose Homeostasis, and Insulin Resistance; J.M. Tunnicliffe, et. al; December 2008
- "Seattle Post-Intelligencer"; New Studies Could Be a Jolt to Rethink Your Coffee Habits; Bob Condor; June 2005
- “Complementary Therapies and the Management of Diabetes and Vascular Disease”; Trisha Dunning; 2006
