MONDAY, Aug. 11, 2008 (HealthDay News) -- Some obese people don't seem to be at increased risk for heart disease, while some normal-weight people have a number of heart disease risk factors, according to two studies.
In the first study, German researchers analyzed 314 people, ages 18 to 69, and divided them into four groups: normal weight, overweight, obese but still sensitive to insulin, and obese with insulin resistance.
People in the overweight and obese groups had more total body and visceral fat (abdominal fat around the organs) than those with normal weight. But obese people with insulin resistance had more fat within their skeletal muscles and their livers than obese people without insulin resistance. Obese people with insulin resistance also had thicker walls in the carotid arteries, an early sign of narrowing of the arteries -- a condition called atherosclerosis.
Insulin sensitivity and artery wall thickness were the same in obese people without insulin resistance and in normal-weight people.
"In conclusion, we provide evidence that a metabolically benign obesity can be identified and that it may protect from insulin resistance and atherosclerosis," Dr. Norbert Stefan and colleagues at the University of Tubingen wrote. "Furthermore, our data suggest that ectopic (misplaced) fat accumulation in the liver may be more important that visceral fat in the determination of such a beneficial phenotype in obesity."
The study was published this week in the journal Archives of Internal Medicine.
In another study in the same issue of the journal, U.S. researchers assessed body weight and cardiometabolic abnormalities (including high blood pressure, elevated triglycerides, and low levels of "good" high-density lipoprotein cholesterol) in 5,440 adults who took part in the National Health and Nutritional Examination Surveys between 1999 and 2004.
People with none or one abnormality were considered metabolically healthy, while those with two or more abnormalities were metabolically abnormal.
"Among U.S. adults 20 years and older, 23.5 percent (approximately 16.3 million adults) of normal-weight adults were metabolically abnormal, whereas 51.3 percent (approximately 35.9 million adults) of overweight adults and 31.7 percent (approximately 19.5 million adults) of obese adults were metabolically healthy," wrote Rachel P. Wildman, of the Albert Einstein College of Medicine, and colleagues.
Normal-weight adults with metabolic abnormalities tended to be older, less physically active, and have larger waists than healthy normal-weight adults, the study said. Obese people with no metabolic abnormalities were more likely to be younger, black, more physically active and have smaller waists than those with metabolic risk factors.
"These data show that a considerable proportion of overweight and obese U.S. adults are metabolically healthy, whereas a considerable proportion of normal-weight adults express a clustering of cardiometabolic abnormalities," the researchers concluded. "Further studies into the behavioral, hormonal or biochemical and genetic mechanisms underlying these differential metabolic responses to body size are needed and will likely further the identification of possible obesity intervention targets and improve cardiovascular disease screening tools."
"Both reports emphasize the benign nature of fat accumulation outside the abdomen," Dr. Lewis Landsberg, of the Northwestern University Comprehensive Center on Obesity in Chicago, wrote in an accompanying editorial.
"In both studies, the detrimental effect of visceral fat accumulation and its surrogate, waist circumference, were clearly demonstrated, confirming older studies showing that waist circumference is a risk factor even in normal-weight individuals," he said.
The studies show it's important to calculate body mass index and measure waist circumference when assessing cardiovascular risk in overweight and obese patients, Landsberg noted.
The U.S. Centers for Disease Control and Prevention has more about heart disease risk factors.