There is the obvious answer of the genetic freak with a metabolism of a nuclear reactor. However, a genetic freak would be a rare occurrence. Otherwise, they wouldn’t be a freak.
A lot of the people who “eat whatever they want and never put on weight” are young, active daily, and most importantly, whatever they want doesn’t entail consuming more calories than they burn.
If they eat junk, but in small portions, they aren’t as likely to gain weight. If they eat a bunch of junk when they are out with friends, but consume a healthy diet at home, then they are less likely to gain weight.
It depends on the situation. It’s rare that a person can over eat constantly without gaining weight.
- The person might be eating a lot when you see them but restricting calories during other meals.
- The person could be very athletic and burning a lot of calories so they can consume a lot during those times.
- A person could be practicing intermittent fasting. This is what I do. I usually eat 2 meals a day. Each meal consists of 1lb (500g) of meat, quite a few carbs, and a lot of veggies. If I’m dining out later in the day I will restrict calories during my first meal and focus on veggies.
It sure seems like some people can eat whatever they want and not gain much weight, while others can’t waver from a strict calorie count without putting on pounds. Research shows that people, who are prone to maintaining their weight, when given more to eat than they need, tend not to gain much weight. Whereas, people who tend to gain weight, when given more to eat than they need, gain more weight. If you have a good set point, your resting metabolic rate goes up when you eat more calories than your body needs, and the extra calories burn off. You do not gain weight.
Metabolism and energy expenditure. Some people are blessed with a high metabolism, which means they burn calories at a higher rate. Metabolism decreases gradually with age (starts declining once we reach maturity), so younger people can usually eat quite a bit more. But those born with a very high metabolism can remain higher than average even as mature adults. Some people also have very high calorie needs due to the amount of energy they burn either through exercise or heavy physical labor.