March 31, 2003 (Chicago) -- Though extra fat often gathers just under the skin, it's the deeper, underlying fat that is most likely to increase the risk for heart attack, according to researchers from Johns Hopkins Medical Institutions in Baltimore.
There are two different types of fat, says Kerry J. Stewart, EdD, professor of clinical exercise physiology at Johns Hopkins. "The fat that is just below the skin is called cutaneous fat, but the really worrisome fat is visceral fat. This is the fat that is found in the [abdomen] and surrounding vital organs."
Visceral fat is the type of fat that is metabolized by the liver, which turns it into cholesterol that circulates in the blood. "Bad" cholesterol, called low-density lipoproteins or LDL, collects in the arteries where it forms plaque, a waxy substance that narrows the arteries.
Stewart says that just being overweight increases the risk for accumulation of visceral fat, but it is not only what you weigh but what you eat that contributes to visceral fat.
He and his colleagues recruited 84 healthy adults (46 women and 38 men) aged 55 to 75 to determine if diet also contributes to visceral fat buildup. All patients were asked to keep food diaries for three days so Stewart and his colleagues could determine the daily calorie intake. The volunteers also underwent magnetic resonance imaging to determine if they had visceral fat. "The MRI can both visualize and measure the amount of visceral fat," says Stewart.
While visceral fat went up as waistlines increased, it was also related to the amount of fat consumed by the volunteers, he says. "Saturated fat is the worst. This is hard fat like lard, butter, or fat on meats," says Stewart. People who said that more than 30% of their calories came from fat were most likely to have measurable visceral fat."
Alice Lichtenstein, DSc, professor of nutrition science and policy at Tufts University School of Medicine in Boston, tells WebMD that the study from Johns Hopkins is "interesting, and it certainly is another reason to begin a weight-reduction program, [but] the observation needs more study." Lichtenstein, who is a spokeswoman for the American Heart Association, says that obese people are also usually sedentary. "So we don't know anything about the exercise component and what effect that might have."
Lichtenstein says rather than trying to limit a particular type of calorie, a better approach to dieting is to limit total calorie intake and increase exercise.
While Stewart agrees that the observation needs more study, he says there are two "take-home messages for consumers: if you are overweight, shape up and at the same time limit your intake of saturated fats."
SOURCE: American College of Cardiology 52nd Annual Scientific Session, poster 1057-148.