Scientists know that the type of fat you can measure with a tape isn't the most dangerous. But what is the most effective way to fight internal, visceral fat that you cannot see or feel? The answer: exercise.

Researchers at UT Southwestern Medical Center analyzed two types of interventions —lifestyle modification (exercise) and pharmacological therpay (medicine) —to learn how best to defeat fat lying deep in the belly. The study is published in Mayo Clinic Proceedings.

"Visceral fat can affect local organs or the entire body system. Systemically it can affect your heart and liver, as well as abdominal organs," said senior author and cardiologist Dr. Ian J. Neeland, assistant professor of internal medicine. "When studies use weight or body mass index (BMI) as a metric, we don't know if the interventions are reducing fat everywhere in the body, or just near the surface."

To find out, the researchers evaluated changes in visceral fat in 3,602 participants over a 6-month period measured by computed tomography (CT) or magnetic resonance imaging (MRI). Both exercise and medicines resulted in less visceral fat, but the reductions were more significant per pound of body weight lost with exercise.

"The location and type of fat is important. If you just measure weight or BMI, you can underestimate the benefit to your health of losing weight," said Dr. Neeland, a Dedman Family Scholar in Clinical Care. "Exercise can actually melt visceral fat."

Participants in exercise trials were 65% female, with a mean age of 54 and mean BMI at enrollment of 31. Exercise regimens were monitored, not self-reported. The majority of exercise trials were performed in the US and Canada, while pharmacologic trials included the US, Canada, Sweden, Japan, and four multinational cohorts. The medications used by study participants were US Food and Drug Administration (FDA) approved or in the FDA approval pipeline.

According to the Centers for Disease Control and Prevention, obesity affects nearly 40% of adult Americans. Dr. Neeland said researchers previously thought of fat as inert storage, but over the years this view evolved and fat is now seen as an active organ. "Some people who are obese get heart disease, diabetes, or metabolic syndrome—and others don't," Dr. Neeland said. "Our study suggests that a combination of approaches can help lower visceral fat and potentially prevent these diseases."