Studies Show Waist Circumference is Heart Risk
Factor Even in Normal-Weight Individuals
Some of obese appear ‘Metabolically Healthy’ without
increased cardiovascular risk
Aug.
11, 2008 - Some obese individuals do not appear to have an increased
risk for heart disease, while some normal-weight individuals experience
a cluster of heart risks, according to two reports in the August 11/25
issue of Archives of Internal Medicine, one of the JAMA/Archives
journals. The studies find a key factor is where the fat is located.
Interestingly, normal-weight individuals with metabolic abnormalities
tended to be older, less physically active and have larger waists.
“The prevalence of obesity is increasing
worldwide, and this epidemic is accompanied by a high incidence of type
2 diabetes mellitus and cardiovascular disease,” the authors write as
background information in one of the articles.
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 to the hormone insulin) and for having an
unhealthy cardiovascular risk profile.
In one study, Norbert Stefan, M.D., and colleagues
at the University of Tübingen, Germany, studied 314 individuals age 18
to 69 (average age 45). The researchers measured participants’ total
body fat, visceral fat (abdominal fat around the internal organs) and
subcutaneous fat (fat under the skin) using magnetic resonance
tomography.
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 two obese groups had
more total body and visceral fat than those at a normal weight, and
there was no difference between the two 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 (narrowing of the arteries, a heart disease risk
factor).
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
[misplaced] fat accumulation in the liver may be more important than
visceral fat in the determination of such a beneficial phenotype in
obesity.”
Second study find
In a second study, Rachel P. Wildman, Ph.D., of the
Albert Einstein College of Medicine, Bronx, N.Y., and colleagues
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
(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,” 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.
“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.”
Editorial: Studies refine understanding of risk
posed by obesity
Both studies attempt to improve the understanding
of obesity, making it a more useful tool for predicting which patients
will develop cardiovascular disease, writes Lewis Landsberg, M.D., of
the Northwestern University Comprehensive Center on Obesity, Chicago, in
an accompanying editorial.
“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, Dr. Landsberg concludes.
Links to More on Senior
Citizens and Obesity in SeniorJournal.com Archives
Aug.
11, 2008 - Some obese individuals do not appear to have an increased
risk for heart disease, while some normal-weight individuals experience
a cluster of heart risks, according to two reports in the August 11/25
issue of Archives of Internal Medicine, one of the JAMA/Archives
journals. The studies find a key factor is where the fat is located.
Interestingly, normal-weight individuals with metabolic abnormalities
tended to be older, less physically active and have larger waists.