OVERWEIGHT? Losing Excess Weight Is More Important Than Trimming Dietary Fat
|Reduce the fat in your diet, particularly
saturated fat. That's the standard prescription for lowering blood cholesterol.
But it doesn't work as well for everyone.
For example, people who are obese20 percent over their ideal
weightneed to trim extra pounds in order to get the full benefit from
trimming dietary fat.
What about people who are overweight but not obese? Would they be better
advised to focus on dropping extra poundsor dropping some dietary fat?
Researchers at the University of Cordoba Medical School in Spain enlisted 41
young men to answer the question, with help from their U.S. colleague, Jose M.
Ordovas. He's at USDA's Human Nutrition Research Center on Aging at Tufts
University in Boston.
Ordovas is a pioneer in assembling a profile of genes involved in heart disease
risk. (See "Attacking
Heart Disease at Its Genetic Base," Agricultural Research, July
1999, pp. 20-21.) "We're trying to customize the prescription for reducing
risk," he says. "It's now a matter of trial and error."
He says genes involved in bodyweight appear to hold sway over genes that
control how blood lipids respond to dietary changes. Losing weight switches off
some weight genes, canceling their effect on the genes that affect blood lipid
levels. In fact, some of the genes involved in this interaction may be the
The researchers tested three diets on the men. Half were overweight, with a
body mass index (BMI) between 25 and 30 kilograms per meter squared (kg/m2).
That's equivalent to a 6-foot man weighing 185-215 pounds, or a 5-foot, 8-inch
man weighing 165-195 lbs.
For 4 weeks, the men ate a high-fat diet: 38 percent fat, 20 percent of which
was saturated fat. Then they switched to the low-fat diet recommended by the
National Cholesterol Education Program (NCEP)28 percent fat, 10 percent
saturated fat. Lastly, they ate another high-fat (38-percent) diet. But instead
of being heavy in saturated fat, it was high in monounsaturated fats (22
percent)the predominant fats in olive and canola oils. These fats are
proving beneficial for the cardiovascular system.
The overweight men began with higher total cholesterol and triglycerides than
the slim group and less "good" HDL cholesterol. Ordovas says blood
lipids are correlated with body weight and BMI.
Both heart-healthy diets were less effective at improving the cholesterol
profile in the overweight men. On the NCEP diet, their total cholesterol drop
was less than half that of the lean men7 percent versus 16 percent.
Likewise, their artery-damaging LDL cholesterol dropped 9 percent, compared to
21 percent for the lean group.
The researchers concluded it's more important for overweight men to lose weight
than to change the fat content of their diets.
The overweight men did have a bigger drop in triglycerides when eating the diet
high in monounsaturated fats. This suggests that portly people should
substitute olive or canola oil for saturated fat.
"High triglycerides are associated with reduced glucose
tolerance"the earliest stage of diabetes, says Ordovas. "And
evidence is mounting that they are an independent risk factor for heart
disease."By Judy McBride,
Agricultural Research Service Information Staff.
This research is part of Human Nutrition, an ARS National Program (#107)
described on the World Wide Web at
Jose M. Ordovas is at the USDA-ARS Jean Mayer Human Nutrition Research Center on Aging at Tufts University, 711 Washington St., Boston, MA 02111; phone (617) 556-3102, fax (617) 556-3103.
"OVERWEIGHT? Losing Excess Weight Is More Important Than Trimming Dietary Fat" was published in the March 2000 issue of Agricultural Research magazine.