So 1,000 calories is about two-thirds of a day's calorie intake for this age group. All the test meals contained 35 percent calories from fat. The older women had higher levels of glucagon. With more sugar available to fuel body processes, the women burned less 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.