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The Truth About Exercise and Your Weight

Find out how fitness really factors in.

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By Miranda Hitti
WebMD Feature

Reviewed by Louise Chang, MD

If you've been working out and eating fewer calories but your extra pounds won't budge, you may be wondering why that seemingly simple strategy isn't working.

The truth is you may need a reality check about what to expect from exercise.

1. Exercise is only part of the weight loss story.

There's no getting around your tab of calories in and calories out.

The obese patients Robert Kushner, MD, clinical director of the Northwestern Comprehensive Center on Obesity, treats often tell him they're not seeing the results they want from exercise.

"They will say, 'I have been working out three days a week for 30 minutes for the past three months, and I have lost 2 pounds. There's something wrong with my metabolism,'" he says.

Kushner tells patients that exercise is very good for them, but for weight loss, he emphasizes starting with a healthy diet. "First, we've got to get a handle on your diet," Kushner says. "As you're losing weight and feel better and get lighter on your feet, we shift more and more toward being more physically active. Then living a physically active lifestyle for the rest of your life is going to be important for keeping your weight off."

Other experts have had success including physical activity early on. But they stress that the amount of exercise is key.

James O. Hill, PhD, director of the Center for Human Nutrition at the University of Colorado at Denver, says it's easier to cut 1,000 calories from a bloated diet than to burn off 1,000 calories through exercise. "But there are many, many studies that show that exercise is associated with weight loss when done in enough volume and consistently," he says. "It depends how much you do."

For Pamela Peeke, spokeswoman for the American College of Sports Medicine's "Exercise is Medicine" campaign, fitness is a crucial part of a weight loss program, but it's for reasons that go beyond calorie burning. She praises its mind-body benefits, which will help with motivation over the long haul.

Peeke asks her patients to start walking as a way to "celebrate" their bodies with activity. "For years, they've blown off their body," Peeke says. "By them actually using their bodies, they can begin to integrate them back into their lives and not use them as a source of torture or torment or shame."

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."

4. Exercise machines may not tell the whole calorie story.

Treadmills and other exercise gear often have monitors that estimate how many calories you're burning.

Kong Chen, director of the metabolic research core at the National Institutes of Health, says those displays are "close, but for each individual they can vary quite a bit."

Chen suggests using calorie displays on exercise equipment for motivation but not as a guideline to how much you can eat.

"It doesn't matter if the display says 300 or 400 calories. If you do that every day or increase from that level, then you've achieved your purpose. But I wouldn’t recommend feeding yourself against that," Chen says.

Those machines don't account for the calories you would have burned anyway without exercising.

"It isn't 220 calories for those 40 minutes of exercise versus zero," Kushner says. "If you were sitting at work or playing with your kids, you’re probably burning 70 calories during that period of time. You have to subtract what you would burn if you didn't exercise. So the overall calorie burn becomes much less."

5. One daily workout may not be enough.

Your best bet for your weight -- and for your overall health -- is to lead a physically active lifestyle that goes above and beyond a brief bout of exercise.

"It's not just about 30 minutes of exercise," Chen says. "It's about fighting the sedentary environment."

"The message isn't that the 30 minutes on the treadmill isn't good," Hill says. "It's that the 30 minutes on the treadmill isn't going to make up for 23-and-a-half sedentary hours." Hill encourages people to weave activity throughout their day. "Do something to move and make it fun," he says.

Chen also recommends setting realistic expectations and taking "small steps all the time" toward your weight goal.

As much as calories-in vs calories-out matters, don't forget about stress, sleep, and other factors that can affect your weight, Williams says. "We need to look at someone's total lifestyle, not just whether someone hits the gym," she says. "Weight and obesity are really multifactorial, and it really simplifies it just to break it down to nutrition and exercise. Those are really big pieces but definitely not the only pieces."