Why Do Certain People Eat A Lot, But Never Gain Weight?

This is one of the greatest injustices in life: some people have to pay careful attention to whatever they eat to control their weight; others, however, can eat donuts at will, and their weight would rarely change. What’s the secret? Why do some people hardly ever gain weight?

Kathleen Melanson, professor of nutrition and food science at University of Rhode Island, said that there’s no simple answer to this question. “It involves genetic, nutritional and even behavioral factors,” Melanson told Live Science, “and the extent of impact may vary with individual differences.”

One of the most important factors is perception. It has nothing to do with body size or metabolism, neither with casting a spell on a full moon night. Melanson said that many people seem to eat whatever they want without gaining weight. In fact, what they really eat is no more than ours. For example, your friend who eats ice cream every day may naturally eat less meals or snacks to offset the heat of ice cream. Or when eating pizza, they eat small pieces very slowly, and they would stop when they’re full.

“If you measure the calorie intake of these people, you will find that they don’t eat as much as you think,” said Dr. Frank Greenway, chief medical officer of the Pennington Biomedical Research Center, “They will eat high-calorie foods, but it is difficult for other people to control themselves when eating this kind of food.”

Exercise also makes a difference, but it is not necessary to sweat in gym. Melanson said: “Some people just move more, even if they are not athletes.” For example, they may be more active, having a manual job, or having to follow their children and run around all day long. Melanson adds that evidence suggests that some people’s genes determine their more willingness to move. Such extra exercise can speed up their bodies’ metabolism. “The more you move”, she said, “the more the number and activity of mitochondria in muscle cells will be. These are the ‘power plants’ that produce energy. And people use this energy for exercise.” The more mitochondria, the more calories will be burnt.