People who are genetically predisposed to storing belly fat, or having an apple-shaped body type, could face a higher risk of type 2 diabetes and heart disease, researchers said.
According to the International Diabetes Foundation there were 2.28 million cases of diabetes in South Africa in 2015.
The study in the Journal of the American Medical Association (JAMA) suggests a person's genetic makeup may cause health problems down the road.
"People vary in their distribution of body fat – some put fat in their belly, which we call abdominal adiposity, and some in their hips and thighs," said senior author Sekar Kathiresan, associate professor of Medicine at Harvard Medical School.
Link between belly fat and diabetes proven
"We tested whether genetic predisposition to abdominal adiposity was associated with the risk for type 2 diabetes and coronary heart disease and found that the answer was a firm 'yes'."
Previous observational studies have uncovered a link between belly fat and type 2 diabetes and heart disease, but fell short of proving cause and effect.
To investigate further, researchers examined six studies conducted from 2007 to 2015, including some 400,000 participants whose genomes were analysed.
Genetics also play a role
Previous research had identified 48 gene variants associated with waist-to-hip ratio, resulting in a genetic risk score.
They found that people with certain genes that predisposed them to higher waist-to-hip ratio also had higher lipids, insulin, glucose and systolic blood pressure, as well as a higher risk for type 2 diabetes and heart disease.
"These results illustrate the power of using genetics as a method of determining the effects of a characteristic like abdominal adiposity on cardiometabolic outcomes," said lead author Connor Emdin, a researcher at Massachusetts General Hospital.
Since researchers did not find any links between body type, genetic risk score and confounding factors such as diet and smoking, that "provides strong evidence that abdominal adiposity itself contributes to causing type 2 diabetes and heart disease," he added.
Emdin said the findings could one day lead to the development of drugs designed to target belly fat, and perhaps lower the risk of diabetes and heart disease.
Fat not the only cause
A new study by the University of Florida is however challenging the notion that type 2 diabetes is a disease of the overweight and obese. In fact, the study authors report that in people over 45, one-third of those at a healthy weight have prediabetes.
"Being at a healthy weight may not necessarily be healthy," said the study's lead author, Arch Mainous, a professor of health services research management and policy at the University of Florida. This means that the medical fraternity should not just be looking for diabetes in the overweight and obese.