"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 senior investigator Samuel Klein from Washington University School of Medicine in St. Louis.
The researchers identified some key measurements that distinguished metabolically normal obese study participants from those with problems. One was the presence of fat inside the liver. Those with abnormal metabolism accumulated fat there.
Another difference involved gene function in fat tissue. People with normal metabolism in spite of their obesity expressed more genes that regulate fat production and accumulation.
"These results suggest that the ability of body fat to expand and increase in a healthy way may protect some people from the metabolic problems associated with obesity and weight gain," Klein said.
The study involved 20 obese participants who were asked to gain about 15 pounds (7 kg) over several months. After gaining weight, the metabolic profiles of the participants remained normal if they were in the normal range when the study began.
But the metabolic profiles significantly worsened in participants whose metabolic profiles already were abnormal when the study got underway. The study was published in The Journal of Clinical Investigation.