Many studies have proven that caffeine makes insulin resistance worse. Although caffeine is often added to popular weight loss drugs, caffeine can make losing weight harder for people with insulin resistance and pre-diabetes.  It makes glucose intolerance worse, causes higher blood sugar, and can contribute to pushing people with pre-diabetes over the edge into full-blown type 2 diabetes.

In a 2002 study published in Diabetes Care, a team of physicians from the Netherlands announced their findings: that caffeine decreased healthy test subjects’ insulin sensitivity by 15%.

In another study reported by MedicineNet.com, people with diabetes were given caffeine pills equivalent to two cups of coffee.  The caffeine alone caused their blood sugar to rise by 8% and was reported higher after every single meal.  This was not true for the control group who did not take caffeine.

According to Suite101.com:

Patients struggling to lose weight and control blood sugar due to a diagnosis of insulin resistance or pre-diabetes should decrease or eliminate dietary caffeine.