Obesity contributes to more than 60 different unhealthy conditions, including diabetes, heart disease, and stroke. Knowing that more than one-third of adults in the United States are obese, researchers from Washington University School of Medicine decided to study the risk these people faced. They published their findings in The Journal of Clinical Investigation.

"This research demonstrates that some obese people are protected from the adverse metabolic effects of moderate weight gain, whereas others are predisposed to develop these problems," said the study’s senior investigator Dr. Samuel Klein, director of Washington University's Center for Human Nutrition, in a press release. "This observation is important clinically because about 25 percent of obese people do not have metabolic complications. Our data shows that these people remain metabolically normal even after they gain additional weight."

Klein and his research team studied 20 obese participants, who were asked to gain approximately 15 pounds over the course of several months in order to determine how the extra weight would affect their risk of disease. Before they started, the subjects’ blood sugar, liver fat, and other risk factors were measured. And then under the supervision of a dietician, subjects ate extra food from fast-food restaurants.

"Our goal was to have research participants consume 1,000 extra calories every day until each gained six percent of his or her body weight," said the study’s co-author Dr. Elisa Fabbrini, assistant professor of medicine at Washington University School of Medicine, in the press release. "This was not easy to do. It is just as difficult to get people to gain weight as it is to get them to lose weight."

Test subjects who were in relatively healthy ranges to begin with weren’t harmed by the weight gain and none of their risk increased. However, those who were already at risk to begin with had significantly worsened once they gained extra weight. Once the study was completed, the test subjects were enrolled in a weight-loss program designed to make sure they lost all of the weight they gained.

Researchers found answers in the type of fat inside participants' liver, which helped the researchers determine whether an obese person was protected or at risk of disease. Another factor was that some people, despite being obese, had normal metabolisms. They were able to metabolize the extra weight in a healthier way than those who had slow or abnormal metabolisms. The research team’s next step is to analyze types of fat, muscle, and liver more closely in order to see why certain obese people are protected from harm’s way.

"We need more studies to try to understand why obesity causes specific diseases in some people but not in others," Klein said. "Could it be genetics, specific dietary intake, physical lifestyle, emotional health, or even the microbes that live in the gut?"

Source: Klein S, Fabbrini E, Yoshino J, et al. Metabolically normal obese people are protected from adverse effects following weight gain. Journal of Clinical Investigation. 2015.