Half of Overweight Adults Are Normal Metabolically

By Michael Smith
NEW YORK, 12 aug 2008-- Obese patients don't necessarily show any signs of the metabolic abnormalities associated with cardiovascular disease, researchers here said.
And almost a quarter of those with a normal weight had two or more of the cardiometabolic abnormalities associated with an increased risk of cardiovascular disease, according to Rachel Wildman, Ph.D., of Albert Einstein College of Medicine and colleagues.
The finding from the National Health and Nutrition Examination Surveys (NHANES) from 1999 through 2004 that nearly a third of obese patients are free of metabolic abnormalities was paralleled by a report from German researchers that shows about 24% of obese people have a "metabolically benign" form of obesity.
In those patients, according to Nobert Stefan, M.D., and colleagues from the University of Tubingen, insulin sensitivity is not different from those of normal weight, nor is the intima-media thickness of the common carotid artery.
Both studies appear in the Aug. 11 issue of Archives of Internal Medicine and "emphasize the benign nature of fat accumulation outside the abdomen," according to Lewis Landsberg, M.D., of Northwestern University in Chicago.
Writing in an accompanying editorial, Dr. Landsberg said the studies also reinforce conventional wisdom that visceral fat accumulation is detrimental to cardiovascular health.
The message for doctors, he said, is that calculating a body mass index and measuring waist circumference remain "valuable tools in the assessment of cardiovascular risk in overweight and obese patients."
Dr. Wildman and colleagues looked at a cross-sectional sample of 5,440 participants in NHANES, and stratified them according to BMI and cardiometabolic abnormalities, including elevated blood pressure; triglycerides, fasting plasma glucose, C-reactive protein, and homeostasis model assessment of insulin resistance value, as well as low levels of high-density lipoprotein cholesterol.
Participants were classified as metabolically normal if they had at most one of those abnormalities, and abnormal if they had two or more, the researchers said.
Extending the results to all U.S. adults 20 or over, the study found:
About 16.3 million normal-weight adults (23.5% ) were metabolically abnormal.
About 35.9 million overweight adults (51.3%) remained metabolically healthy.
And about 19.5 million obese adults -- or about 31.7% -- were also metabolically healthy.
Among normal-weight people, older age, lower physical activity, and larger waist circumference were independent correlates of cardiometabolic abnormalities, the researchers said.
On the other hand, the independent correlates of metabolic health among overweight and obese people were younger age, non-Hispanic black race or ethnicity, higher physical activity levels, and smaller waist circumference, they found.
In the German study, Dr. Stefan and colleagues studied 314 patients taking part in a study of the pathophysiological mechanisms of type 2 diabetes. Of those, 54 had a BMI in the normal range, 133 were overweight, and 127 were obese.
When the researchers measured insulin sensitivity, 31 of the obese participants (or 24%) were in the upper quartile -- and were not significantly different from those with a normal body mass index. They were classified as obese, but insulin sensitive.
As expected, total body and visceral fat were significantly higher (P<0.05) in the overweight and obese groups compared with the normal-weight group, but the insulin-sensitive and insulin-resistant obese groups were not different.
On the other hand, compared with the insulin-resistant group, the insulin-sensitive obese participants had significantly lower ectopic fat in skeletal muscle lower fat in the liver (4.3% versus 9.5%), and lower intima-media thickness of the common carotid artery (0.54 versus 0.59 millimeters), all at P<0.05.
At the same time, their insulin sensitivity was 17.4 versus 7.3 (arbitrary units), a difference that was significant at P<0.05.
The unexpected finding, Dr. Stefan and colleagues said, was that the insulin sensitivity and the intima-media thickness of the insulin-sensitive obese group were similar those of the normal BMI participants -- 18.2 arbitrary units and 0.51 millimeters, respectively.
The findings show that "a metabolically benign obesity that is not accompanied by insulin resistance and early atherosclerosis exists in humans," Dr. Stefan and colleagues concluded.
The German study was supported by the Deutsche Forschungsgemeinschaft and European Network on Functional Genomics of Type 2 Diabetes. The researchers reported no conflicts.
The U.S. researchers did not report external support for their study and made no financial disclosures.
Dr. Landsberg reported no financial conflicts.
Primary source: Archives of Internal MedicineSource reference:Stefan N, et al "Identification and characterization of metabolically benign obesity in humans" Arch Intern Med 2008; 168(15): 1609-1616. Additional source: Archives of Internal MedicineSource reference: Wildman RP, et al "The obese without cardiometabolic risk factor clustering and the normal weight with cardiometabolic risk factor clustering: prevalence and correlates of 2 phenotypes among the U.S. population (NHANES 1999-2004)" Arch Intern Med 2008; 168(15): 1617-1624. Additional source: Archives of Internal MedicineSource reference: Landsberg L "Body fat distribution and cardiovascular risk: a tale of 2 sites" Arch Intern Med 2008; 168(15): 1607-1608.