2. Exercise is a must for weight maintenance.
"I come back to this over and over and over," Hill says. "You can't find very many people maintaining a healthy weight who aren't regular exercisers. What we find is that people who focus on diet aren't very successful in the long run without also focusing on physical activity."
Hill warns that people can be "wildly successful temporarily" at losing weight through diet alone. But there's plenty of data that show that those people regain the weight if they aren't physically active.
Timothy Church, MD, director of preventive medicine research at the Pennington Biomedical Research Center in Baton Rouge, La. says, "When it comes to weight, you can't talk about diet alone, and you can't talk about exercise alone. You absolutely have to address both issues at the same time."
3. Food splurges may undo your efforts.
Exercise may not buy you as much calorie wiggle room as you think.
"The average person overestimates the amount of activity they're doing by about 30% and underestimates their food intake by about 30%," says Kathianne Sellers Williams, a registered dietitian and personal trainer.
"When' I'm looking at people's food and activity logs, sometimes things just don't add up," she says. "People think, 'Oh, I just did 60 minutes at the gym' or 'I just did 30 minutes at the gym' and think that counteracts a lot of what they're eating. But the reality is our food portions are huge."
Plus, Peeke says, you have to look at all the other calories you ate or drank that day and how sedentary you were apart from your workout.
"The rest of the day, you're sitting down and you're also eating other things," Peeke says. "How are you going to burn that stuff, let alone this extra little treat that you just thought you wanted?"
It's hard to accurately estimate how many calories you burn working out, Church says. "If it is a hard workout," he says, "you kind of intuitively think, 'Wow! That's cool! I just put enough in the bank for two days!' and you really haven't."