It’s been known for a while that a spare tire around the midsection is more of a risk for cardiac-health problems than a flatter stomach. A recently released study says it may be because extra belly fat can affect the kidneys, increasing blood pressure.

Dr. Aslan Turer, an interventional cardiologist at University of Texas Southwestern Medical Center, followed 900 Dallas individuals for seven years. He and his colleagues used abdominal magnetic resonance imaging to assess abdominal fat at the start of the study, published in the Journal of the American College of Cardiology.

Individuals with high levels of fat in the abdominal cavity and around their abdominal organs were far more likely to develop high blood pressure, during the course of the study than individuals with lower amounts of this abdominal fat, irrespective of their overall amount of body fat.

The researchers hypothesize that “retroperitoneal fat” interferes with kidney function.

“Retroperitoneal fat is fat around the kidneys and adrenal glands, which hypothetically could be involved with the pathogenesis of hypertension, since these organs regulate the blood pressure,” Dr. Turer said.

“Perhaps more important than how much weight a person gains, is where the fat is stored. Fat around the kidneys may be a particularly bad actor,” Dr. Turer said. 

Too much fat in the midsection also puts people at higher risk of high cholesterol and diabetes, which can increase the risk of heart attack and stroke, according to the American Heart Association.