Obesity Doesn't Always Equal Diabetes
FRIDAY, Aug. 24 -- Obesity doesn't mean a person is destined to develop diabetes, experiments in mice suggest. Instead, it may all depend on where the fat is stored.
Mice that overate and were very obese still didn't become diabetic, because the activity of two hormones let them store extra calories in fat tissue rather than in their livers or heart muscle.
"What this mouse model shows is what we have appreciated clinically for a while," said lead researcher Philipp Scherer, a professor of internal medicine and director of the Touchstone Center for Diabetes Research at the University of Texas Southwestern Medical Center at Dallas.
"Basically, it shows that for individuals who have the ability to expand their adipose [fat] tissue mass appropriately for the number of calories they take up, those individuals fare much better than someone who has a more reduced capacity to expand their adipose tissue," Scherer said.
If fat isn't stored in the adipose tissue, it ends up in the liver and muscles. That, in turn, causes significant insulin resistance that can lead to diabetes, Scherer explained.
In their experiments, Scherer's team showed that in genetically altered mice, an excess of adiponectin, a hormone linked to sensitivity to insulin, and a deficiency in leptin, a hormone that suppresses appetite, causes the mice to store excess calories in fat tissue instead of in liver, heart or muscle tissues, according to the report in the Aug. 23 online edition of the Journal of Clinical Investigation.
Scherer noted that in people as in mice, where fat is stored is largely determined by genetics. "You have a lot of obese individuals who are not type 2 diabetics, and you have lean individuals that can be type 2 diabetics," he said. Type 2 diabetes is the most common form of the disease, and it is most often tied to overweight or obesity.
All of this means that measuring fat as an indicator of general health might not hold up anymore, Scherer said. "It's really a matter of where we deposit these excess calories," he said. "Fat is a little like real estate, it's all about location, location, location."
Scherer hopes the outcome of his work will be finding ways to manipulate how and where fat is stored in people.
However, none of this should be seen as a free pass to become obese, Scherer said. "Exercise and reduction of food intake are the best ways to stay healthy," he said. "Most people can't prevent some fat from being stored in the liver and muscle," he added.
One expert agreed the finding does mimic what is seen in some people.
"It's too bad, we ain't mice," said Dr. Larry Deeb, president for medicine and science at the American Diabetes Association. "Clinically, there are people who are like those mice. They are significantly overweight, and yet, they don't have the insulin resistance," he said.
There might be therapeutic implications to this finding, if it could lead to a better understanding of why some people can become obese and not develop diabetes, and others don't, Deeb said.
However, there are other health consequences to being overweight besides diabetes, he noted. "Obese people wear out the knees and strain the heart and lungs and other body systems," Deeb said. "In addition, their quality of life suffers."
For more on diabetes, visit the American Diabetes Association.
Posted: August 2007