Not every obese person is unhealthy.
More than one-third of American adults with BMIs north of 30 also have a higher risk for developing conditions like type 2 diabetes, heart disease and stroke than the general population. But a small sliver of obese adults defy the odds, maintaining metabolic health despite the excess weight.
Scientist don’t yet fully understand the biophysical mechanisms behind “fat but fit” or “healthy obese” -- and there’s even some disagreement about whether or not a healthy obese person can maintain their status over a lifetime. Two recent and unrelated analyses of metabolically healthy, yet obese people illustrate the disagreement among experts.
The first, an experiment published Jan. 2 in the The Journal of Clinical Investigation, examined how added weight affects metabolic health. The researchers asked obese subjects to actually gain 6 percent of their body weights -- an average of 15 pounds -- over the course of several months.
The researchers found that obese participants who had begun the experiment with “metabolically normal” levels of insulin resistance, cholesterol levels, blood pressure and liver fat maintained their metabolic health, while the participants who were “metabolically abnormal” before the fast food binge continued to deteriorate over the course of the experiment.
In other words, if they were healthy before the weight gain, they were healthy after.
The study's lead investigator, Dr. Samuel Klein of the Washington University School of Medicine told HuffPost that the most important takeaway about his study is simply the demonstration that yes, metabolically healthy obese people really do exist and they continue to resist the deleterious metabolic effects of moderate weight gain.
But a separate study concluded that “healthy obesity” is merely a preliminary stage of unhealthy obesity. In this analysis, researchers looked at the health data of 2,521 employees over the course of 20 years.
Lead author and obesity researcher Joshua Bell of University College London classified 66 of the obese employees as “metabolically healthy” because of their cholesterol levels, blood pressure, fasting glucose levels and insulin resistance. By the end of the 20 year period, only 34 remained in that category; most of the rest joined the ranks of the “unhealthy obese” over time. The analysis was published in the January issue of the Journal of the American College of Cardiology.
“Healthy obese adults are far more likely to become unhealthy obese than [are] healthy or unhealthy non-obese adults, indicating that healthy obesity is often just a phase,” wrote lead author Joshua Bell of University College London to The Huffington Post.
“Often” might be the salient word here. Klein pointed out that Bell’s study also had metabolically healthy people in it after 20 years.
“About 40 percent of people considered to be ‘metabolically healthy’ at baseline were still metabolically healthy 20 years later,” Klein said of Bell’s analysis. “This demonstrates a remarkable stability of metabolic health among a subset of [about] 15 percent of the original obese population."
Even if this super population can maintain metabolic health indefinitely, no medical professional would advocate for or consider weight gain innocuous. Klein, despite his assertion that obese people can be healthy, called childhood obesity the “most alarming issue for the future,” and described adult obesity as the “single most important public health problem in the United States,” where about 69 percent of adults are either overweight or obese.
In the best case scenario, “health” in an obesity context relates only to the relationship between obesity and metabolic health, meaning the link between excess fat and the risk of diabetes and cardiovascular disease. Other obesity-related health complications, like cancer, arthritis and respiratory disease remain risks.
“Even though obese people who are metabolically healthy will probably not get much metabolic health benefits by losing weight, weight loss could reduce their risk of cancer, allow them to get pregnant, improve their arthritis, enhance their physical function and improve their quality of life,” said Klein.