Thin people don’t sit still.

At the Endocrine Research Unit of the Mayo Clinic, in Rochester, Minnesota, a study of 20 self-proclaimed couch potatoes — half of whom were lean, half mildly obese — revealed that the thin volunteers were more likely to stand, walk, and fidget. The researchers noted that the obese participants sat, on average, more than two hours longer every day than the lean ones did.

“If the obese subjects took on the activity levels of the lean volunteers, they could burn through about 350 calories more a day without working out,” says endocrinologist James Levine, the lead author of the study. “Over a year, this alone could result in a weight loss of approximately 30 pounds, if calorie intake remained the same.”

Simply moving around more, taking walks during the workday, and parking your car at the far end of the parking lot can burn many calories. But regular exercise is important, too. “Ninety percent of people who maintain their weight are exercising in a way that’s the equivalent of walking four miles a day,” says registered dietitian Elizabeth Somer, the author of 10 Habits That Mess Up a Woman’s Diet (McGraw-Hill, $17, www.amazon.com).

Johnson, for instance, does “some yoga stretching and light weights in the morning.” Then, she says, “I combine a run with walking my son to the bus. I’ll usually get some aerobic exercise every day.”

Regular workouts have another dividend: “Exercise makes you more aware of your body,” psychologist Stephen Gullo says. “You’re less likely to eat the chocolate cake that you know will take hours to burn off on the treadmill.”