A man eats junk food

"When you observe somebody who doesn't seem to gain weight, they're not defying the laws of thermodynamics, the laws of physics," one expert says. (Getty Images)

You know people like this, or at least you think you do. They gorge on burgers and candy and cake, never seem to move from the couch and yet maintain a perfectly trim figure.

But according to diet experts, such a person hasn't discovered some magic spell to avoid weight gain. Weight loss and management – apart from potential biological factors – come down to what people eat and how much activity they include in their daily lives.

"When you observe somebody who doesn't seem to gain weight, they're not defying the laws of thermodynamics, the laws of physics," says U.S. News Best Diets expert panelist Dr. Larry Cheskin, the director of the Johns Hopkins Weight Management Center. What they're doing, in some fashion, is balancing their intake and output, he adds.

This phenomenon is very common in young children, Cheskin says. For example, if kids choose to go run around the block, they'll likely come back and eat more than they normally would. But then they won't repeat those same eating habits for the rest of the week.

Someone who seems to not have to watch what they're eating as an adult is achieving such a balance. Some people say they can eat what they want but if you truly scrutinize their lifestyle, you’d find they eat small portions of food and that they limit the high-fat, high-sugary foods in their eating plans, according to registered dietitian Rebecca Reeves an adjunct assistant professor at the University of Texas School of Public Health in Austin, Texas and also a U.S. News Best Diets expert panelist. They probably could eat whatever they want, but they know how to moderate the intake.

Reeves also says these people are probably active in some way, even if it's just walking three or four times a week, an hour at a time, or avoiding a sedentary life by being busy or active during the day. You'd be surprised how many calories you burn even doing things like taking the stairs, she says.

Cheskin notes the standard exercise recommendation is to get a half hour of moderate physical activity – like walking at a brisk pace – on most if not all days, and that people who are more physically active have lower risks of heart disease, diabetes and high blood pressure.

Cheskin points out people who don't seem to gain weight may have favorable biological factors, like a faster metabolism, more lean tissue or more muscle mass. Inherently they may be able to burn more calories. Reeves says she doesn't think people can cop out and blame their excess weight all on genetics, and believes they can cope with their body structure and layer good eating habits and physical activity on top of that.

With all that in mind, what is a more efficient way to lose weight? Both Cheskin and Reeves suggest a number of strategies, including seeking help from weight-management professionals.

Reeves warns you shouldn't think idealistically regarding weight-loss goals; the goal is that you want to be healthy. You should start, she says, by monitoring what you're eating. "It’s a lot easier to cut 500 calories out of your diet" than it is to work off those 500 calories, Cheskin says. You can eat in three minutes what it would take you an hour and a half at the gym to burn off.

If you're struggling beyond that, Cheskin says you should remember you're not alone. In addition to the role genetics and metabolism play, he notes that the U.S. is an environment constantly pushing us in the wrong direction. Most people don't have trouble getting enough calories given the food options in the U.S., not to mention that this is a culture where no one is going to make you be physically active or eat healthy. It's not just that our habits are bad, but that our society makes it easier to stray.

So the next time you see that person pigging out on unhealthy food, know that they're not a superhero. And maybe invite them to join you for a walk.

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Best Weight-Loss Diets

Rank Diet Name
Weight Watchers Diet
Volumetrics Diet
Jenny Craig Diet
Vegan Diet
The Flexitarian Diet
The Engine 2 Diet
Ornish Diet
Raw Food Diet
SlimFast Diet

Diet Ranking information as of April 3rd, 2018

Tags: health, weight loss, diets, diet and nutrition, food and drink

David Oliver is a social media associate editor at U.S. News & World Report. Follow him on Twitter, connect with him on LinkedIn, or send him an email at doliver@usnews.com.

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