A pair of reports in the latest issue of Archives of Internal Medicine finds that obese individuals do not appear to have an increased risk for heart disease, while some normal-weight individuals experience a cluster of heart risks.

Research indicates that in addition to overall obesity, the way body fat is distributed may influence risk for heart disease and diabetes.

For instance, individuals with fat within the abdominal cavity -- estimated by measuring waist size -- appear to be at higher risk for insulin resistance (a pre-diabetic condition that occurs when the body fails to respond insulin) and for having an unhealthy cardiovascular risk profile.

In one study, researchers from the University of Tubingen, Germany, studied 314 individuals age 18 to 69. They measured participants' total body fat, visceral fat -- abdominal fat around the internal organs -- and subcutaneous fat, which is the fat under the skin. Insulin resistance was measured using an oral glucose tolerance test.

The individuals were then divided into four groups: normal weight, overweight, obese but still sensitive to insulin and obese with insulin resistance.

Those in the overweight and obese groups had more total body and visceral fat than those at a normal weight, and there was no difference between obese groups. However, obese individuals with insulin resistance had more fat within their skeletal muscles and their livers than obese individuals without insulin resistance.

In addition, those who were insulin-resistant had thicker walls in their carotid arteries, an early sign of atherosclerosis. Individuals in the obese--insulin sensitive group did not differ from the normal-weight group in insulin sensitivity or artery wall thickness, the authors note.

"In conclusion, we provide evidence that a metabolically benign obesity can be identified and that it may protect from insulin resistance and atherosclerosis," they write. "Furthermore, our data suggest that ectopic fat accumulation in the liver may be more important than visceral fat in the determination of such a beneficial phenotype in obesity."

In a second study, scientists at the Albert Einstein College of Medicine, Bronx, N.Y., assessed body weight and cardiometabolic abnormalities, including high blood pressure, elevated triglycerides and low high-density lipoprotein or "good" cholesterol, in 5,440 individuals participating in the National Health and Nutritional Examination Surveys between 1999 and 2004. Participants were considered metabolically healthy if they had none or one abnormality and metabolically abnormal if they had two or more abnormalities.

"Among U.S. adults 20 years and older, 23.5 percent of normal-weight adults were metabolically abnormal, whereas 51.3 percent of overweight adults and 31.7 percent of obese adults were metabolically healthy," the authors write.

Normal-weight individuals with metabolic abnormalities tended to be older, less physically active and have larger waists than healthy normal-weight individuals. Obese individuals 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 authors write.

In an accompanying editorial, Lewis Landsberg, M.D., of the Northwestern University Comprehensive Center on Obesity, Chicago, notes that both studies attempt to improve the understanding of obesity, making it a more useful tool for predicting which patients will develop cardiovascular disease.

"Both reports emphasize the benign nature of fat accumulation outside the abdomen," he writes. "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."

The message for practicing clinicians is that calculating body mass index and measuring waist circumference are valuable tools in assessing cardiovascular risk in overweight and obese patients, Landsberg said.