Overweight and healthy: the concept of metabolically healthy obesity

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Carrying too many pounds is a solid signal of current or future health problems. But not for everyone. Some people who are overweight or obese mange to escape the usual hazards, at least temporarily. This weight subgroup has even earned its own moniker—metabolically healthy obesity.

Health professionals define overweight as a body-mass index (BMI) between 25.0 and 29.9, and obesity as a BMI of 30 or higher. (BMI is a measure of weight that takes height into consideration. You can calculate your BMI here.)

Most people who are overweight or obese show potentially unhealthy changes in metabolism. These include high blood pressure or high cholesterol, which damage arteries in the heart and elsewhere. Another harmful metabolic change is resistance to the hormone insulin, which leads to high blood sugar. As a result, people who are overweight or obese are usually at high risk for having a heart attack or stroke, developing type 2 diabetes, or suffering from a host of other life-changing conditions.

But some people who are overweight or obese manage to avoid these changes and, at least metabolically, look like individuals with healthy weights. “Obesity isn’t a homogeneous condition,” says Dr. Frank Hu, professor of nutrition and epidemiology at the Harvard School of Public Health. “It appears that it doesn’t affect everyone in the same ways.”

Dr. Hu and three colleagues wrote a “Personal View” article in Lancet Diabetes and Endocrinology reviewing what is known about metabolically healthy obesity. They identified several characteristics of metabolically healthy obesity. These include a high BMI with

• a waist size of no more than 40 inches for a man or 35 inches for a woman
• normal blood pressure, cholesterol, and blood sugar
• normal sensitivity to insulin
• good physical fitness

BMI isn’t perfect

BMI is not a perfect measure of weight or obesity. It often identifies fit, muscular people as being overweight or obese. That’s because muscle is more dense than fat, and so weighs more. But muscle tissue burns blood sugar, a good thing, while fat tissue converts blood sugar into fat and stores it, a not-so-good thing.

“Further exploration of metabolically healthy obesity could help us fine-tune the implications of obesity,” says Dr. Hu. “It supports the idea that we shouldn’t use BMI as the sole yardstick for health, and must consider other factors.”

Genes certainly play a role in how a person’s body and metabolism respond to weight. Some people may be genetically protected from developing insulin resistance. Others are genetically programmed to store fat in the hips or thighs, which is less metabolically hazardous than storing fat around the abdomen.

The concept of metabolically healthy obesity could be used to help guide treatment. Currently, exercise and a healthy diet are the foundation for treating obesity. When those efforts aren’t enough, weight-loss surgery (bariatric surgery) is sometimes an option. Such surgery is appropriate for people with metabolically unhealthy obesity, the authors suggest, but for people with metabolically healthy obesity it might make more sense to intensify the lifestyle approach rather than have surgery. This idea, however, needs to be tested in clinical studies, says Dr Hu.

Don’t rest easy

Metabolically healthy obesity isn’t common. And it may not be permanent, warns Dr. Hu. Just because a person has metabolically healthy obesity at one point doesn’t it will stay that way. With aging, a slowdown in exercise, or other changes, metabolically healthy obesity can morph into its harmful counterpart.

It’s also important to keep in mind that obesity can harm more than just metabolism. Excess weight can damage knee and hip joints, lead to sleep apnea and respiratory problems, and contributes to the development of several cancers.

Bottom line? Obesity isn’t good, even if it’s the metabolically healthy kind.