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All abdominal fat is not created equal.
Take two postmenopausal women, both sedentary, both obese. Their body mass index (BMI) measurements are identical. Both have large abdomens. One woman can pinch her own fat because it's nearer to the surface—subcutaneous fat. The other woman's fat is deeper, closer to her internal organs—visceral fat. What difference does their fat depth make to their health?
Plenty, according to a new study in the November 2004 issue of Journal of Clinical Endocrinology & Metabolism.1
"We found that where the body fat is stored was the main determinant of who had the metabolic syndrome," says principal investigator Barbara Nicklas, PhD, associate professor of internal medicine at Wake Forest University in Winston-Salem, N.C. Metabolic syndrome is a constellation of signs and symptoms, including hypertension, high lipids, insulin resistance, and excess weight.
LOCATION, LOCATION
Nicklas and her colleagues examined 58 obese, postmenopausal women; all were sedentary, weight-stable, and nonsmokers. Women with a variety of medical conditions, including diabetes, were excluded. Average BMI was 33. Of these women, half met the criteria for metabolic syndrome.
It's been well documented that having a pear-shaped body (lower location of body fat, lower waist size, larger hips) is healthier than having an apple shape (fat higher on waist). This study goes a step further.
"We were not just looking at whether the fat was carried on the hips or in the abdomen," Nicklas says. "We determined whether abdominal fat was stored between the skin and the abdominal muscle wall, or stored as visceral fat.
"There was a dramatic difference in percentage of visceral fat between those women with metabolic syndrome and the other women in the study. Women with metabolic syndrome had 33% more visceral fat, but were similar in all other respects, including the waist circumference, with almost exactly the same amount of subcutaneous fat and identical fat cell size."
The metabolic syndrome occurs in 24% of adults in the United States and in 44% of those aged 60–69 years, Nicklas says. Although the metabolic syndrome is more prevalent in obese people, many obese people don't have the condition: Some may have only one or two of the components, or none.
In addition to body composition and fat distribution, the researchers also looked to determine whether aerobic fitness and inflammation differed between women with and without the metabolic syndrome.
They noted that previous studies show that the metabolic syndrome is related to low aerobic fitness in healthy individuals but wrote, "We did not see a significant relationship between the metabolic syndrome and aerobic fitness in these women. The range of fitness levels may not have been large enough to see an association with metabolic syndrome."
They found no difference in body weight, body fat, waist size, or hip size.
They found a significant difference in one of four inflammatory markers measured and the number of metabolic syndrome components in study subjects. But the intra-abdominal fat findings were the most striking.
Visceral fat is not currently a component of metabolic syndrome diagnosis. However, Nicklas says, "More studies are needed to determine whether measurement of visceral fat could be used by doctors for more accurate prediction of cardiovascular disease in obese individuals."
FINDING (AND LOSING) VISCERAL FAT
Why do people store fat differently? Nicklas believes heredity is probably the biggest influence. However, those with a higher percentage of visceral fat can reduce their risk.
For these people, exercising may be more important than dieting: "High-intensity exercise seems to preferentially reduce visceral fat," Nicklas says. Weight loss by any means is good, however. "When people lose weight, they lose it from everywhere."
Health care providers should take note, Nicklas emphasizes. "Weight loss should be recommended strongly for people with higher intra-abdominal fat."
But how does a practitioner know that an obese patient is storing fat viscerally? Not by just looking. Imaging studies—by computed tomography (CT) or magnetic resonance imaging (MRI)—are the only means of measuring visceral fat.
Should imaging studies be part of routine orders for obese patients at risk, or is the cost prohibitive? "The cost range [for CT] is a couple-hundred dollars on average," Nicklas says. "It's not out of the question.... We may need to someday use CT as a diagnostic tool."
Nicklas calls for more research on why fat is stored in visceral areas, and
how to treat it. She adds that drugs that may target intra-abdominal fat do
exist, but none has been approved by the Food and Drug Administration.
References
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