Diet vs. Exercise: A Healthy Habit Showdown

Want to lose weight? The advice most often given is to diet and exercise, but it turns out that one aspect is far more important than the other. While both are key to living a long, healthy life, ultimately, nutrition experts say you can't outrun a poor diet.

The reality is that the only way to lose weight is to burn more calories than you take in, which is nearly impossible to do unless you change your eating habits. "A pound of fat is 3,500 calories," says Wayne Andersen, medical director of the meal replacement company Medifast and co-founder of the weight-loss coaching program Take Shape for Life. "Running a marathon burns 2,600 calories. That's how ineffective exercise is for losing weight."

[Read: No, There's Not a Magic Pill for Weight Loss.]

That's not to say that exercise isn't important -- but if you absolutely have to choose between the two, the evidence is clear that diet plays a much bigger role in weight loss. "It's so easy to consume large doses of calories when something like a burger and fries can have more than 1,200 calories," says Angela Fitch, director of Medical Weight Loss at the University of Cincinnati Health Weight Loss Center. "The only way you're going to lose weight is to be more mindful of your calories, because we are notoriously poor at estimating how many calories we consume."

So how many calories should we be eating? Probably a lot less than you think, Fitch says. "Women should be eating around 1,500 calories per day to lose weight, men a little more," she says. "The key to sticking to that limit is eating many more fruits and vegetables."

[Read: How to Turn Your Phone Into the Ultimate Weight-Loss Tool.]

And while going to the gym will help you burn more calories, Andersen says, most people tend to put the calories right back on, almost negating their workout. "When you go to the gym and burn off 400 calories and then go eat a 1,000-calorie dinner, you wasted your time," he says.

One calorie bomb that Fitch advises people to cut out of their diet is beer. "A craft beer can have upwards of 500 calories," she says. "It's easy to drink that in 10 minutes, but it's not easy to burn off. You'd have to do two to three hours of walking, or spend more than an hour on the bike."

Another way of looking at calories is by what they equate to in healthy food, Fitch says. "500 calories is a lot of apples," she says. "You'd be very full from eating that much fruit, but you're not when you drink those calories in a beer. It's just more of a reason to increase your intake of healthy food."

[See: U.S. News Best Diets for Healthy Eating.]

And as a bonus, decreasing your calories and increasing your intake of fruits and vegetables offers double the benefit. "You get so much more bang for your buck," Fitch says. "You'll lose weight and get all the health benefits of these foods."

Once you have your diet down, adding exercise can help you see results faster, Fitch says. "People who do 150 minutes of physical activity per week lose more than those who don't," she says. "The most interesting part is that the time is additive." So someone who works out in five 10-minute intervals would see the same benefit as someone who works out for 50 minutes straight.

[Read: Stay Fit Without Setting Foot in The Gym.]

For that reason, it's easier and more sustainable to make lifestyle changes rather than sign up for the gym, which many people stop going to after only a few months. "Start taking the stairs every day, or park a little further from work," Fitch says. "These things add up and eventually become a healthy habit."

In the end, losing weight is about small victories -- everything you do adds up to create meaningful change, Andersen says. "It's very difficult, but you can do it," he says. "It requires time and effort, but the payoff is huge."

Amir Khan is a Health + Wellness reporter at U.S. News. You can follow him on Twitter, connect with him on LinkedIn or email him at akhan@usnews.com.

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