And there is a small group of people who are going to be obese no matter what they do. But the vast majority fall somewhere in between. Whether they can maintain a healthy body weight depends, in large part, on how much effort they are willing to put into it. Genes and physiology play a role in how easy or difficult that is going to be, Hill says. Genes don't dictate weight but help set the upper and lower weight limits, experts say.
Genes affect how the body is going to relate to the environment.
He'll be bigger than most guys his height. But if he eats a low-fat diet and gets plenty of exercise, he'll probably settle at 190 to 200 pounds, Wadden says. On the other hand, if he spends most weekends on the couch, watching football and chowing down, he'll settle at 220 to 230 pounds. Eating and exercise habits make a difference even if someone has a genetic predisposition to obesity, Wadden says. Studies have shown that some people gain weight more easily than others.