Little physical activity and dieting can make the fat cells produce a hormone believed to activate HDL (good) cholesterol production, say researchers.
"What we're learning is that even overweight people who are physically active and eating a healthy diet are getting benefits from the lifestyle change," said principal investigator Christie Ballantyne, M.D., director of Methodist's Center for Cardiovascular Disease Prevention.
"When you exercise and diet, you're improving the function of your adipose tissue, your heart and vascular systems, and even muscle performance. You're getting a lot of benefits that you may not see by just looking at the weight on a scale," he explained.
Ballantyne said that while a causal relationship between adiponectin production and increases in blood HDL cholesterol levels is not yet proven, this latest study supports models putting the fat hormone somewhere in the controlling pathway of liver HDL cholesterol synthesis. Adiponectin's role in fat burning and sugar storage is well established.
Ballantyne and his team examined patient data from Look AHEAD, a randomized, multi-center clinical trial examining the effect of a lifestyle intervention designed to produce weight loss on risk for cardiovascular disease.
To be eligible for Look AHEAD, participants must have been diagnosed with type 2 diabetes, and also deemed overweight or obese.
Participants were assigned to either an "intensive lifestyle intervention" program in which they were encouraged to become more physically active and to limit their calorie intake or a program including diabetes support and education.
Look AHEAD participants have had their blood drawn at regular intervals, with testing for various biomarkers, including HDL cholesterol and the fat hormone adiponectin, in its many forms. Study participants are also weighed and given a fitness (exercise stress) test.
After one year, Look AHEAD participants' adiposity (a measure of total fat), fitness, blood glucose levels, and fat levels were, on average, significantly improved.
Levels of LDL, the so-called "bad cholesterol," did not change. But Adiponectin levels and HDL cholesterol did. Total adiponectin produced by fat cells increased about 12 percent relative to a control group, in which people received diabetes and obesity education but no intensive lifestyle modification. And HDL cholesterol went up nearly 10 percent.
HDL cholesterol correlates positively with overall cardiovascular health. It is not yet known for sure whether low HDL cholesterol causes cardiovascular problems, or whether both (low HDL and CV problems) are controlled in parallel by another, as-yet-unknown effector.
The finding will appear in an upcoming issue of the Journal of Lipid Research (now online).