If you’ve switched to decaf coffee thinking it’s better for your health, you might be surprised to hear a recent study found caffeinated coffee may be healthier. The researchers conducting the study certainly were.

The Coffee and Lipoprotein Metabolism study conducted at the Fuqua Heart Center in Atlanta looked at the impact of both regular and decaffeinated coffee on key markers of heart health. The study found that decaf, but not regular coffee, could raise levels of bad cholesterol.

The study’s acronym, CALM, reflects what researchers expected to find.

”We had thought that decaffeinated coffee was healthier than caffeinated coffee because of the caffeine content,” says Dr. Robert Superko, the lead author of the study. ”We know that in regards to the increase in fatty acids, and bad LDL cholesterol that that’s not the case. And that’s a very surprising finding.”

The study randomly assigned 187 people to one of three groups: one that drank three to six cups of regular coffee a day, one that drank three to six cups of decaf, and a third, the control group, that drank no coffee.

The researchers measured caffeine levels in the blood as well as levels of other key heart-health indicators, including blood pressure, heart rate and cholesterol. After three months, the decaffeinated group experienced a rise in apolipoprotein B, a protein associated with bad cholesterol.

Levels of non-esterified fatty acids, a fat in the blood that can lead to increased cholesterol levels, also increased among decaf drinkers. Superko says it’s not the caffeine that makes the difference.

”Whether coffee has caffeine is not the only thing that differentiates caffeinated from decaffeinated types,” Superko says. ”Caffeinated coffee, by and large, comes from a bean species called coffee Arabica, while many decaffeinated coffees are made from coffee Robusta. The decaffeination process can extract flavanoids and ingredients that give coffee flavor. So decaffeinated brands use a bean that has a more robust flavor.”

Researchers also found that levels of HDL2, a type of good cholesterol associated with a lower risk of heart disease, were affected by decaf. Overall, there were no significant differences in HDL2 levels among the three groups. But in the decaffeinated group, there were major differences depending on the amount of body fat.

For overweight individuals drinking decaf, HDL2 levels increased about 50 percent. But for those with normal weight, HDL2 levels dropped 30 percent.

The study found no significant differences in blood pressure or any of the other markers of heart health among the three groups.

So what does that mean for the average coffee drinker?

”If you only drink one cup each day, the results of our study probably have little relevance because at that level your daily coffee dose is relatively low,” Superko says.

People concerned about their fatty acid and LDL cholesterol levels may want to avoid decaf coffee. But Superko does not recommend overweight individuals drink decaf to boost HDL levels.

”It is far more important to exercise and lose excess body fat because that will increase HDL, the good cholesterol, and HDL2 even more than decaffeinated coffee,” he says.