Caffeine and Insulin Sensitivity

Caffeine and Insulin Sensitivity  (full text PDF free till end of the month)

A number of reports have observed that acute caffeine ingestion decreases glucose tolerance and insulin sensitivity, and have raised the question whether its increased consumption throughout the world in the form of coffee and cola beverages might be of public health concern in the development of type 2 diabetes. Although some epidemiologic studies have found strong associations between coffee intake and detrimental lifestyle factors that favor obesity and diabetes, it is interesting that in spite of this, they have demonstrated that increased coffee consumption is associated with a decreased risk of developing type 2 diabetes.  When lifestyle confounders are taken into account, individuals consuming 6 cups coffee per day have at least 50% less risk of developing type 2 diabetes than those consuming 2 cups per day. Although it is perhaps premature to recommend increased coffee or caffeine intake to prevent the development of type 2 diabetes, there is little or no evidence to warrant the recommendation that it should not be a part of a normal healthy diet.

This is an interesting summary article.  In the section entitled Caffeine and Carbohydrate Metabolism, a case for acute caffeine consumption impairing glucose tolerance by inducing insulin resistance (decreases glucose uptake) is laid out which goes counter to the results of the coffee study highlighted above.   Perhaps it's something else in the coffee?  

More modest inverse associations were also observed for decaffeinated coffee consumption, caffeine intake from noncoffee sources, and total caffeine intake, as well as the incidence of type 2 diabetes, suggesting that caffeine and other components of coffee contribute to this inverse relationship.

Seems in part the case.  The authors discuss the conflicting short term "laboratory measured" effects and those seen in epidemiologic studies.

... it is very obvious that the results and conclusions of the acute and epidemiologic studies do not agree, and this illustrates the problem of extrapolating shortterm observations to a chronic disease (with an etiology that is influenced by a variety of interacting genetic and lifestyle factors.)

This seems even more surprising given the rather strong correlation between coffee intake and other lifestyle factors that are deleterious such as drinking, poor diet, etc.  Below I've summarized in bullet point fashion how the authors believe increased coffee intake decreases the risk of developing T2:

• Caffeine stimulates resting metabolic rate.  It could be as simple as fewer coffee drinkers getting overweight?
• Caffeine increases epinepherine
• Caffeine + epinepherine act together to promote lypolysis leading to an increase in plasma free fatty acid levels. (<- at first glance this might seem to not be a good thing)
• C+E have a thermogenic effect.  (thus the FFA's are likely readily oxidized with the boosted metabolism)
• The combined effects increase lipid turnover (less ROS hanging around??) "which may in the long-term have beneficial effects on body weight, body composition, and substrate use that could help to prevent the development of glucose intolerance, insulin resistance, and diabetes."

They go on:

However, such arguments are very speculative, and it may well be that the observed acute effects of coffee or caffeine on glucose tolerance and insulin sensitivity are suppressed by habituation to its repeated consumption.  Indeed, repeated caffeine consumption over 5 days induces complete tolerance to its effects on blood pressure, heart rate, and, in particular, blood glucose concentrations.52 

They also consider the other components of coffee:

• Coffee contains many bioactive compounds, most of which have as yet unknown metabolic effects.
• Coffee contains a quinide that improves insulin-mediated glucose uptake in rats
• Phenolic compounds in coffee influence GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide I) levels.  (These two peptides are called incretins and are associated with beta cell proliferation and decreased apoptosis (death) 

"Consequently, the combined physiologic effects of coffee’s many components may well be very different from that of one of the components studied alone."

Posted by CarbSane after her third very large mug of coffee 8*)