(ran SP edition)
Most Americans grow fatter and fatter as they age even if they don't gain a pound. The amount of fat on the average American body doubles between the age of 20 and the 50s.
In the first study of its kind, a federal researcher has found something that may shed new light on why fat and age increase together.
It appears that people lose some of their ability to use fat as an energy source as they age if the fat calories come from large meals and that the excess fat is deposited in reserves in the body.
In a small study the researcher found that older women burn far fewer fat calories than younger women after eating a large meal but burn about the same after eating a small one.
To avoid gaining fat with age, women should eat several small meals a day, the study's authors suggest.
One reason people gain fat as they age may be the loss of muscle that comes with aging and decreasing physical activity. It takes both muscle and physical activity to burn fat calories.
Another possible factor: As they age, people tend to get a larger share of their calories from fat even as their total consumption of calories decreases.
According to Dr. Susan Roberts, the federal researcher who did the fat-burning study, the increase in body fat may be enough to increase the average person's risk of heart disease and Type 2 (adult-onset) diabetes.
Roberts and her associates at the Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center in Boston, where she is chief of the energy metabolism laboratory, say they suspect that as people age they slowly lose some of their ability to use fat as an energy source. Unused fat calories are deposited throughout the body.
Roberts said there is evidence that older men lose some of their ability to burn off the fat calories they get from overeating even when they step up their exercise levels, but what about after small meals? How does the aging body cope with fat calories from snacks and small meals?
Just fine, it appears.
In an experiment designed to measure fat metabolism after meals, the Roberts research team recruited eight women in their 20s and eight in their 60s and early 70s.
They ate identical meals, and their breath and urine were analyzed to measure their ability to burn off fat, carbohydrate and protein calories after each meal.
The meals consisted of peanut butter and jelly sandwiches and milk, with 17 percent of the calories from protein, 35 percent from fat and 48 percent from carbohydrates.
Caloric content of each meal was adjusted by changing the size of the sandwiches and the size of the glass of milk.
The metabolic changes were measured after fasting and after meals of 250, 500 and 1,000 calories.
Laboratory tests of the women's breath and urine showed how many calories they burned from fat, carbohydrate and protein.
The main finding: Fat was burned much more slowly among the older women after the 1,000-calorie meal than it was among the younger women.
That indicates that the older women's bodies were overwhelmed by the fat load in the heavier meal.
In fact, the older women burned the same amount of fat after the 1,000-calorie meal as they did after the 500-calorie meal.
After the 250- and 500-calorie meals, the older and younger women burned the same amount of fat calories.
Roberts said that, because the study was small _ only 16 women _ and the first to measure fat-burning after meals rather than during fasting, the findings can't be considered conclusive until other scientists duplicate the results.
She said she suspects that age-related hormonal changes may have something to do with the inability to convert fat from large meals into energy.
However, she said the findings indicate that people hoping to avoid middle-age spread and the health risks associated with age-related obesity should eat smaller, more frequent meals.
The study indicates that 250-calorie snacks and small 500-calorie meals would be effective. Women in their 60s and 70s typically consume about 1,400 to 1,500 calories a day.
A 1,000-calorie meal represents about two-thirds of a day's calorie intake for those women. "It simulates going out to a restaurant and having a big meal," Roberts said.
What if you feel you must eat a large meal?
Make sure most of the calories come from carbohydrates _ fruits, vegetables, cereal grains and beans _ suggests Dr. Arthur Leon, director of the University of Minnesota's Laboratory of Physiological Hygiene.
There are good studies showing that the body turns very few excess carbohydrate calories from large meals into body fat, Leon said. A bonus is that the carbohydrates, along with the fiber from fruits and vegetables, tend to suppress the appetite and create a feeling of fullness, Leon said.