You’re craving your favorite cookies as you browse the aisle at the local grocery store. To your delight, you find a low-fat version. Should you pile a few boxes in your cart and head home with what you believe is a healthier version of your favorite treat?

Maybe not, says a team of researchers from the University of Georgia who found some so-called diet foods contain higher amounts of sugar despite a reduction in fat content. The study was published online in the journal Physiology and Behavior.

The study involved three groups of rats. The first were fed a high-fat, high-sugar diet, the second a low-fat, high-sugar diet and the third a balanced rodent diet. Over a four-week period, the team tracked body weight and composition, calorie intake and fecal samples. The results among the high-fat, high-sugar and low-fat, high-sugar rats were very similar: Both groups gained weight and body fat. They also had an increase in fat in the liver, something that can lead to nonalcoholic fatty liver disease in humans. The third group of rats experienced no adverse health effects.

The team also noted the rats fed a low-fat, high-sugar diet consumed about as many calories as the balanced-diet group — yet they built up body fat more than twice as fast.

The study adds to the team’s previous research that focused on the role high-fat diets may play on the body’s collection of microbes in the digestive tract, or gut microbiome. The new study indicates a low-fat, high-sugar diet may lead to a buildup of gut bacteria linked to liver damage.

So, when you check nutritional labels, pay attention to the fat content, but focus more on the sugar amount. That tasty treat could come at a cost.