Is caffeine a friend or a foe when it comes to weight loss? Does it increase blood sugar and insulin or decrease it? What about its impact on cortisol? If you love coffee or tea and are challenged with excess weight and are pre-diabetic or diabetic it is difficult to make a good decision. Just when we think we know the answer, someone does a study seeming to prove the opposite is in fact true. And they are often poles apart.
Does caffeine promote insulin resistance and Type 2 diabetes? The answer is yes, says James Lane, PhD in an article in the April, 2011 edition of the "Journal of Caffeine Research" in which he reviews the literature on this issue. Lane states that as many as 17 studies show a connection between ingesting caffeine and increased insulin resistance or impaired glucose tolerance. This means coffee and tea drinking could lead to weight gain and eventual development of type 2 diabetes.
Other research supports these results. A 2011 study in the Journal of Nutrition found that consumption of fat along with caffeine resulted in decreased glucose tolerance.
On the other hand, a 2009 article published by Rachel Huxley, D. Phil. of the George Institute for International Health in Australia concluded just the opposite. She and her colleagues did an analysis of research on the association between the risk of diabetes and coffee consumption conducted between 1966 and 2009. They concluded that diabetes risk fell 7% for each cup of coffee consumed during a day. Risk was also less for decaf coffee and tea drinkers. The decaf connection suggests coffee may contain elements besides caffeine associated with risk of type 2 diabetes.
Why the different results? Lane's literature review was of experimental studies which involved administering caffeine and measuring an outcome such as resulting glucose levels. Huxley's review was of epidemiological studies looking at caffeine consumption on the one hand and diabetes risk in large groups of people. While the results are suggestive it is more difficult to say the relationship is causal. The connection between decaf and reduced risk is interesting and suggestive of directions for future research on other elements of coffee or tea which may support good health.
Caffeine may cause high levels of cortisol, another route through which it may contribute to weight gain and blood sugar problems. To evaluate whether individuals may develop a tolerance to caffeine (thereby reducing cortisol secretions), a study published in 2005 in the journal "Psychosomatic Medicine" compared cortisol secretions after 5 days of caffeine ingestion and after 5 days of abstinence. Results showed strong cortisol response after 5 days of abstinence. Five days of caffeine ingestion removed the cortisol response in the morning, but not at 1:00 pm when additional caffeine did cause a response. This suggests there is increased potential for weight gain or blood sugar problems after multiple cups of coffee or other caffeinated drinks.
If your goal is weight loss and/or maintenance of healthy blood sugar levels should you avoid caffeine? The answer may be that it would be a prudent decision. The 7% reduction in risk in the Huxley study is not enough to justify drinking additional caffeinated beverages…especially given the results of the studies reviewed by Lane.