Big Meals May Contribute to Body Fat in Older PeopleBy
WASHINGTON, Oct. 6--As people age, they may be able to
reduce their risk of gaining weight by eating smaller, more frequent
meals, according to U.S. Department of
Agriculture findings reported in the October issue of the American
Journal of Clinical Nutrition.
In the study comparing the fat-burning ability of eight women in
their 20s with another eight in their 60s and 70s, the seniors kept
pace with their juniors after eating 250- and 500-calorie meals. But
they couldn't match the fat-burning rate of the younger group after a
1,000-calorie meal. Fat oxidation was about 30 percent lower in the
older women after the big meal.
"Dietary fat that doesn't get burned gets stored as body fat,"
said I. Miley Gonzalez, Under Secretary for
Research, Education, and
Economics. "That's what happens when older people
overindulge. So the scientists recommend that seniors eat fewer
calories at a sitting, but eat more often to ensure getting enough
Study leader Susan Roberts heads energy metabolism research at the
Jean Mayer USDA Human Nutrition
Research Center on Aging at Tufts University in Boston.
Roberts said the study is the first to measure fat oxidation after
eating, noting that further studies are needed to confirm the
findings. She and colleagues are conducting the research--funded by
USDA's Agricultural Research
Service--to get at underlying causes behind the age-related
increase in body fat.
"Body fat typically doubles between the ages of 20 and 50 to 60
years," she explained. That increase is linked to several
diseases, including cardiovascular disease and non-insulin dependent
diabetes. Several studies suggest a drop in fat oxidation may play a
role, said Roberts.
The women in the study ate two peanut butter and jelly sandwiches
plus a large glass of milk to get 1,000 calories, which represents a
moderately large meal, Roberts said. On average, U.S. women in their
60s and 70s consume about 1,400 to 1,500 calories a day, according to
the latest USDA survey data. So 1,000 calories is about two-thirds of
a day's calorie intake for this age group. "It simulates going
out to a restaurant and having a big meal," Roberts noted.
She said the 250-calorie meal, representing a snack, and the
500-calorie meal, representing a small meal, were also peanut and
jelly sandwiches and milk, but in smaller portions. All the test meals
contained 35 percent calories from fat.
Roberts believes the drop in fat-burning ability is due to hormonal
changes. The older women had higher levels of glucagon. This hormone
triggers the release of sugar into the blood--the opposite effect of
insulin. With more sugar available to fuel body processes, the women
burned less fat. "That's not good," said Roberts, "because
you want to get rid of the fat."
She cited several factors that could contribute to the drop in fat
reduction. Older people have less skeletal muscle, the primary site of
fat oxidation. They also are less physically active and thus don't
burn as much fat. In addition, they tend to eat higher-fat diets.
The scientists suggest that older people exercise to increase
skeletal muscle and fitness. This may offset the fat-burning
deficiency by increasing their capacity to burn fat while resting.
In earlier studies comparing energy metabolism in young and older
men, Roberts found that basal, or resting, metabolism doesn't increase
in older men when they overeat as it does in young men. This also
helps explain why body fat creeps up with age.
Scientific contact: Susan R. Roberts, PhD, chief,
Metabolism Laboratory, Jean
Mayer USDA Human Nutrition Research Center on Aging, Boston, MA
02111, phone (617) 556-3237; fax (617) 556-3224,