Obese Versus Healthy: Better Measurements of Fat

Slender woman eyes closed eating a strawberry pie
Laurence Monneret/The Image Bank/Getty Images

Obesity is almost universally defined by body mass index or BMI. BMI is used to predict the risk of heart disease and other chronic diseases. The higher the number, the greater the risk. To be considered overweight, BMI must be between 25 and 29, and to be considered obese, BMI must be a score of 30 and above. Although BMI is based on weight and height, it doesn’t distinguish fat from muscle. An athlete may have a relatively high BMI simply because muscle is heavier than fat. This is not someone who needs to lose weight by adopting a low-fat diet. BMI is not necessarily a good indicator of risk in seniors, as weight loss is as likely to be caused by a reduction in muscle and bone mass as by a reduction in fat. Moreover, research published in Lancet medical journal on August 19, 2006, showed that those with a low ​BMI had a higher risk of heart attack than those with high BMI.

Waist to Hip Ratio

So perhaps a better measure of body fat is our waist-to-hip ratio, which takes into account body shape, where being pear-shaped is healthier than being apple-shaped. Abdominal fat, or ​visceral fat, is considered to be the most dangerous type of fat since it lies deeper in the body than subcutaneous fat (fat stored beneath the skin), surrounding vital organs like the heart and liver, putting us at even greater risk of heart disease, ​​insulin resistance, and diabetes. Far from being stored passively, visceral fat produces chemicals and hormones that can interfere with the way our organs function.

The Fat Within

Even if you lack the tell-tale belly fat, you still might not be as healthy as you think. Looking slim is one thing, but being healthy is quite another. Research in the U.K. suggests that being a normal weight doesn’t necessarily mean all is well. U.K. scientists have created fat maps of nearly 800 people using MRI (magnetic resonance imaging) machines. Close to half the women and more than half the men with normal BMI scores had excessive levels of internal fat deposited around the heart and liver and streaked through under-used muscles—much like a well-marbled steak.

Doctors suspect that diet alone is not enough to protect our bodies from disease, and fat-free foods can actually be problematic. While dieting may help to look good in your summer bathing suit, it could also cause the body to change the way it stores fat. Those who turned out to have excess fat on the inside tended to be sedentary and generally ate poorly—though not always in excess.

Body Volume Index

With BMI and even waist-to-hip ratio falling short, expect to hear more about the Body Volume Index, or BVI, created by UK-based Select Research, and used in the Body Benchmark Study. This study plans to scan more than 20,000 volunteers in the U.K. and U.S. over two years, using a white-light body scanner to create three-dimensional images showing fat and muscle distribution, to determine the relative risk of disease. This way, doctors can see who’s fat and who’s not, whether they are overweight, normal weight or even underweight.

What You Can Do to Avoid Being Fat on the Inside

  • Eat a diet low in saturated fat, and avoid artificial trans fats
  • Choose lean cuts of meat and poultry
  • Limit total fat intake, and choose unsaturated fats such as olive oil, walnuts, and flaxseeds
  • Eat fish at least twice a week
  • Choose whole grains, legumes, and plenty of fruits and vegetables, preferably organic
  • Control portion sizes—two slices of pizza, not the whole pie
  • Drink plenty of water
  • Get moving—walk, run, bike, chase the kids, swim—whatever feels right