WEDNESDAY, Oct. 6 (HealthDay News) -- Differences in the way body fat grows may explain why increased belly fat appears to boost the risk for certain diseases while extra pounds on the thighs and other parts of the lower body decrease the risk, a new study suggests.

The study included 28 volunteers who were allowed to eat almost anything they wanted -- including ice cream, candy bars and high-calorie drinks -- for eight weeks. On average, the participants put on 5.5 pounds of upper body fat and 3.3 pounds of lower body fat, Mayo Clinic researchers reported in this week's online issue of the Proceedings of the National Academy of Sciences.

"The cellular mechanisms are different," lead author and endocrinologist Dr. Michael Jensen said in a Mayo news release. "The accumulation of abdominal fat happens largely by individual cells expanding in size, while with fat gain in the femoral or lower body, it's the number of fat cells that increases. So, different mechanism, different impact."

The findings challenge the idea that the number of fat cells remain stable in adults, Jensen and colleagues pointed out in the news release.

The results also added support to the theory that an increase in production of lower-body fat cells may somehow help protect the upper body, which in turn may help prevent what is known as metabolic disease, the study authors noted.

A person can develop metabolic syndrome when a group of conditions -- including high blood pressure, unhealthy cholesterol levels, insulin resistance and extra body fat around the waist -- occur together, and increase the risk for heart disease, diabetes and other conditions, according to information from the American Heart Association.

More information

The U.S. National Institute of Diabetes and Digestive and Kidney Diseases offers weight loss tips.