When transplanted deep into the abdomen, fat taken from just under the skin comes with metabolic benefits, or at least it does in mice, reveals a new study in the May issue of Cell Metabolism, a Cell Press publication.
"We started out thinking we would find that any fat inside the abdomen is bad," said C. Ronald Kahn of Harvard Medical School. "What we found was really not what we expected. It appears that visceral fat is not as bad as subcutaneous fat is good."
Earlier studies had established a link between the presence of intra-abdominal, or visceral, fat and "metabolic syndrome" in humans. Increased amounts of subcutaneous fat, on the other hand, had been associated with improved insulin sensitivity and a lower risk of developing type 2 diabetes, among other benefits.
Visceral and subcutaneous fat show major differences in the genes they express, studies also showed. Given the differences in their locations in the body, the two types of fat cells are also exposed to different environments. For instance, they differ in their exposure to various hormones and growth factors and in their nutrient and oxygen supply.
"This raises the question: Are the metabolic effects associated with visceral fat versus subcutaneous fat due to anatomic location or to cell-autonomous differences between these adipose depots"" the researchers said.
To find out, the researchers used a fat transplantation strategy in which they transplanted either visceral or subcutaneous fat from donor mice into either visceral or peripheral subcutaneous regions of recipient mice and examined the effects on both whole-body and cellular metabolism.
Mice that underwent transplantation of subcutaneous fat into the visceral cavity exhibited decreases in body weight, total fat mass accumulation, and fat cell size after several weeks even though they continued to eat just as much and weren't any more active. These mice also showed improved blood sugar and insulin levels in comparison to mice that had undergone a "sham" operation.