We know that carrying around extra weight puts your heart health at risk. New research presented on Friday to the European Society for Cardiology shows that the location of your fat is just as important as the amount of it.
Adults with normal body mass index (BMI) and extra belly fat (termed “central obesity”) had a 79 percent higher risk of major cardiovascular events, compared to people who were mildly overweight but with normal fat distribution. This includes heart attack, stroke and death.
The study of nearly 1,700 citizens of Rochester, Minnesota, with 16 years of follow-up quantifies a risk that doctors already know about: There’s something about belly fat that makes it more dangerous than fat anywhere else.
Individuals with more belly fat, even with normal or near-normal weight, have above average rates of heart disease and diabetes. They have earlier overall mortality. Small studies have shown that individuals with central obesity are more likely to have worse cholesterol values, higher markers of inflammation and even lower resting metabolic rate than those without it.
What makes central obesity so bad?
This is an area of active research. There is probably more than one factor at play.
For the most part, central obesity is associated with low relative muscle mass, a sign of poor health. People with central obesity have extra fat inside the abdomen, surrounding the internal organs. This is known as visceral fat and it’s different than subcutaneous fat, or the fat just below the skin. Visceral fat tends to accumulate more in response to a high-stress state and in people with a sedentary lifestyle, both of which are linked to worse health outcomes.
What’s more, scientists are now exploring the concept of “lipotoxicity.” Visceral fat cells may release more fatty acids than other fat cells. These fatty acids also drain directly into the liver, where they collect and are distributed throughout the circulation. Free fatty acid build-up in the cells of the heart, pancreas and liver lead to problems with these organs -- decreased heart function, impaired processing of cholesterol and poor regulation of blood sugar. These issues, in addition to putting someone at risk for heart disease and diabetes, are associated with diminished tolerance for exercise and tendency to gain more weight. It’s a vicious cycle.
Central obesity is sometimes, but not always, a sign of a hormone or metabolism disorder. That’s another reason to see a doctor about belly fat.
There’s probably a genetic component too. People with a set of features termed “metabolic syndrome” are predisposed to hold onto their extra fat primarily in the midsection, giving these individuals the so-called “apple-shaped” body. People with the metabolic syndrome also have higher rates of diabetes, high blood pressure and heart disease. Whether they are at higher risk as a result of central obesity or whether there is another inherited process driving both weight gain and these disease conditions is the subject of ongoing research.
Diagnosing central obesity
Doctors diagnose central obesity using the most basic of tools: a measuring tape. The waist circumference is measured at the navel with the belly relaxed. For women, risk of heart attack and other conditions increases when the waist circumference is more than 35 centimeters. For men, the number is 40 centimeters. Some also measure the ratio of the waist circumference to the circumference of the hips at the widest point, called the waist-to-hip ratio.
Is belly size more important than body mass index (BMI)?
Most doctors think that knowing both of these numbers -- waist size and BMI -- will offer the best assessment of health status. BMI is a ratio of weight to height, measured in kilograms per meter squared. A healthy BMI is classified as between 18.5 and 24.9. Unfortunately, BMI does not tell you where those pounds are coming from. BMI can inappropriately classify well-trained athletes as overweight -- since muscle weighs more than fat. BMI can also underestimate the amount of excess fat, and therefore possibly underestimate heart disease risk, in people with dramatically low muscle mass.
That’s why physicians recommend aiming for both a healthy weight and a healthy waist.
The good news is that both can be improved with the same strategies. If you smoke, quit. Exercise regularly -- the AHA and USPSTF recommend 150 minutes of intentional aerobic activity per week. Choose a healthy diet -- full of lean meats, protein sources like nuts and beans, a variety of colorful vegetables and a limited amount of whole grain foods.
What do you do about your current waist size? Here’s a good rule of thumb: if your waist is bigger than your hips -- see your doctor to discuss your heart health risk.
Dr. Kelly Arps is a resident physician in internal medicine at Johns Hopkins Hospital. Kelly is working with the ABC News Medical Unit.