Drinking four or more cups of coffee a day appears to be associated with a lower risk of type 2-diabetes and better insulin function and these benefits appear to be largely due to caffeine. That’s the scoop from Harvard researchers. Also, it’s not the first time that research has shown that caffeine consumption improves insulin metabolism and protects against diabetes; a disorder that affects at least 17 million Americans.
A few years ago scientists at Vrije University in Amsterdam reported that heavy coffee drinkers are half as likely to develop diabetes as people who consume two cups or less a day. These findings set off a major controversy. It motivated the Harvard researchers to try to replicate similar findings in a comprehensive analysis, this time using 100,000-plus men and women whose health was monitored for about two decades. The results of this study by the scientists at Harvard were very interesting, to say the least.
The notion that caffeine/coffee consumption could improve insulin metabolism has been a revelation. It flies directly against the data on this topic that shows acute administration of caffeine decreases insulin sensitivity and impairs glucose tolerance. On the other hand, caffeine is known to stimulate thermogenesis and increases energy expenditure. These factors suggest caffeine/coffee improve fat metabolism which in turn would have a beneficial effect on insulin function. However, one important consideration is the tolerance factor. As the body develops a rapid tolerance to habitual caffeine consumption, would it still provide health benefits over the long-term? Now we have enough evidence to make an informed opinion.
Although caffeine is coffee’s best-known ingredient, it’s not the only one. The results of the Harvard study are pertinent because this consideration is taken into account. Coffee contains substantial amounts of magnesium, niacin, potassium, and even antioxidants such as tocopherol (vitamin E). Therefore, the Harvard team tried to tease out the effects of caffeine, as opposed to some of these other substances in coffee. The Harvard team looked at not only coffee drinkers but also tea and decaffeinated coffee drinkers. Decaf’ coffee has the same amount of these other substances, but less caffeine. Tea has other substances and is relatively low in caffeine.
The Harvard study analysis was based on data collected from 42,888 male healthcare professionals from 1986 to 1998 and 85,056 female nurses from 1980 to 1998. All of the men and women were free of diabetes, cancer and cardiovascular disease at baseline. Every two to four years, the participants filled out validated dietary questionnaires that included items on coffee consumption. Over the course of the study, 1,333 men and 4,085 women developed type 2-diabetes. Using a Cox proportional hazard model that adjusted for age, body mass index, smoking, and other diabetes risk factors as well as for fiber and fat intake, the researchers revealed the following facts.
- Men who drink six or more cups of coffee a day were less than half as likely to develop diabetes compared with non-drinkers. Drinking four to six cups helps too. It reduced the risk by 29%.
- Women who consume four cups or more a day also reduced their risk of developing the disease by about 30%. But in their case, six cups did not seem to be any more protective than four cups. Tea, on the other hand, had no impact on diabetes risk, the study showed.
- Decaf coffee was associated with a modest reduction in risk for those who drank four cups or more a day. But those results were not controlled for the amount of regular coffee that was consumed.
- The researchers then looked at total caffeine intake from coffee, colas, and other foods and found that it too appeared to protect against the development of diabetes. Men and women in the highest quintile of caffeine intake were 22% and 30% less likely to develop diabetes, respectively, compared with those in the lowest quintile.
The strengths of this study included large cohorts, long follow-ups and repeated and validated measures of diet and lifestyle. However, the limitations included self-reporting, but the scientist’s validation research suggest the data is good. Also by eliminating individuals with any major disease at baseline, the study addresses the potential confounding effect of pre-existing conditions on diabetes risk. Other scientists that have reviewed the Harvard research concede that the study is thorough. It provides accurate data about the participant’s coffee habits over 10 to 15 years. Plus, this study evaluated tea and decaf coffee, which other studies did not.
Therefore, it appears quite clear that coffee but particularly caffeine consumption has a protective effect against type 2-diabetes, a condition that is a result of poor insulin function. However, could caffeine improve insulin metabolism in healthy people like bodybuilders? The results of some other studies have revealed this may be possible.
A low glycemic response to meals means that blood glucose and insulin levels are controlled. This effect simultaneously promotes fat metabolism and prolongs the life of insulin-like growth factors in circulation. Therefore, people who want to build muscle while shedding body fat need to control blood glucose and insulin responses in their daily diet. This aspect is crucial if a lean, muscular physique is the goal.
The findings from a small study recently completed in the U.K. have shown that coffee/caffeine improves insulin function and carbohydrate (glucose) metabolism in a small group of healthy people, in a manner that would promote better fat loss and muscle gains. Researchers from the University of Surrey reported that caffeine and other compounds in coffee such as chlorogenic acid lower the glycemic response of food consumption in the small number of individuals tested.
This study used a three-way, randomized, crossover study with nine healthy volunteers that consumed either 25 grams of glucose in solution (a control), or 25 grams of glucose in caffeinated or decaffeinated coffee. Blood was frequently tested over the following three hours after consumption.
Results showed that both caffeinated and decaffeinated coffee significantly slowed secretion of glucose-dependent insulinotropic polypeptide compared with the control group, thus lowering the glycemic index (GI) response to the carbohydrate. The differences in plasma glucose, insulin, and gastrointestinal hormone profiles obtained in this study confirmed the potent biological action of caffeine on insulin/glucose metabolism.
The GI is a numerical system of measuring how fast a food or ingredient triggers a rise in circulating blood glucose; the higher the GI, the greater the blood sugar response. Coffee/caffeine consumption appears to lower the GI and insulin response of a meal, an effect that would promote better fat metabolism. Conclusive data is yet to be obtained on this topic, but based on these results I see no reason why caffeine consumption after a meal would not provide better fat loss and muscle gains due to its favorable effects on insulin metabolism.
The take home message for bodybuilders and others that desire a lean, mean physique is that caffeine consumption, particularly after a meal may promote better fat metabolism. It’s a simple strategy that may have noticeable benefits, particularly if a calorie-controlled diet is followed. This topic is a very exciting area of research, so I’ll keep a close eye on the studies that emerge and keep you up to speed.
Sources: American Journal of Clinical Nutrition; American Diabetes Association 63rd Scientific Session.
