WASHINGTON (Reuter) - Older people who have trouble losing weight might try dumping their three squares a day in favor of eating smaller meals more often, researchers advised on Tuesday. A U.S. Agriculture Department (USDA) study found that older people cannot burn fat as efficiently as younger people when they get food in big doses -- which could explain middle-aged spread. "Dietary fat that doesn't get burned gets stored as body fat," Miley Gonzalez of the USDA said. "That's what happens when older people overindulge." The study, published in the American Journal of Clinical Nutrition, found that women in their 60s and 70s burned fat at a rate 30 percent lower than women in their 20s. The 16 volunteers in the study ate two peanut butter and jelly sandwiches with a large glass of milk to get 1,000 calories. "It simulates going out to a restaurant and having a big meal," said Susan Roberts, who led the study. Most older women only eat about 1,500 calories a day so this was a big part of their intake. Volunteers also ate a 250-calorie meal and a 500--calorie meal. All the meals got 35 percent of calories from fat. The older women burned fat at the same rate as younger women when they ate the smaller meals, but their ability to burn off fat dropped with the larger meal. The older women also had higher levels of glucagon, a hormone that triggers the release of sugar into the blood. This gave the body more fuel and less incentive to burn fat. "That's not good because you want to get rid of the fat," Roberts said. Most people do gain weight as they get older but experts recommend gaining no more than 11 pounds (5 kg) between early adulthood and middle age.