In a 14-year study of more than 15,000 people, normal-weight men with big bellies – also known as central obesity – were twice as likely to die compared to men who were obese. Women with normal weights and big bellies were 32 percent more likely to die than obese women, according to the research, which was led by Mayo Clinic cardiologist Francisco Lopez-Jimenez.
Previous research has suggested that central obesity is linked to increased total and cardiovascular death. Those with extra stomach fat have less muscle mass, which is associated with higher mortality risk and metabolic dysregulation.
Not all fat is equal, moreover.
Just as there are “good” and “bad” types of cholesterol, there are different types of fat, Lopez-Jimenez said. “The fat around the belly might look the same under the microscope as fat from the arms or legs, but it’s much more active.”
Belly fat appears to be especially unhealthy, because it’s often deposited in the liver, where it makes inflammatory substances that contribute to heart disease and diabetes, Lopez-Jimenez added.
So just how big a belly is considered risky?
People can calculate their waist-hip ratio (WHR) by dividing their waist measurement by their hip measurement, Lopez-Jimenez said.
Men are considered to have “central obesity” if their waist-hip ratio is 0.9 or more, according to the World Health Organization (WHO). In women, central obesity is defined as a ratio of 0.85 or more.
“Often times, we think if we’re a normal weight, then we’re OK,” said Leslie Cho, head of preventive cardiology at the Cleveland Clinic, who wasn’t involved in the new study, published in Annals of Internal Medicine.
“But weight is not as important as your level of fitness and where you hold your fat.”
The study is a reminder of the limitations of assessing a person’s risk of heart disease or death with only the body mass index, or BMI, Cho added.
The BMI is a ratio of weight and height. A BMI of 18.5 to 24.9 is considered healthy; a BMI of 25 to 29.9 suggests overweight; while a BMI over 30 indicates obesity.
“If you just look at BMI, you’re not getting the whole picture,” said Martin Binks, a spokesman for the Obesity Society and an associate professor of nutritional sciences at Texas Tech University in Lubbock.
“If someone has 50 pounds of body fat spread all over their body, they have a very different risk profile than if the fat is all in their stomach,” Binks said.
Lopez-Jimenez nevertheless noted that fat deposited below the belt – on the legs and buttocks – appears to offer some protection for the heart, although doctors aren’t sure why.
He said that his team’s findings suggest that persons with normal-weight central obesity may represent an important target population for lifestyle modification and other preventive strategies.
People should be conscious of their waist-hip measurements and strive to build muscle, rather than just shed pounds, he added.
“When people lose weight, some of their weight they lose will be muscle mass, if they don’t exercise,” Lopez-Jimenez said. “If you just lose weight but don’t build muscle, you may not be improving your health that much.”