The 3 Most Dangerous Words in Weight Management

Why diet matters more to your waistline than exercise

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"Because I exercised."

For folks trying to lose or maintain their weight, those three words are dangerous. Our perception of the virtues of exercise often makes us feel as if we deserve or have earned more—an extra helping, an indulgent sweet, or, in my case, a beer or two.

But at what cost?

The calories burned through exercise are anything but fair. To be blunt, you simply can't outrun your fork. What you can consume in minutes might easily take you hours to burn off, yet many people consider exercise to be the bigger player in weight management.

Perhaps the belief comes from television shows like The Biggest Loser. Each episode ends with a "last chance" workout—as if a few hours of overly aggressive gym work will immediately translate into weight loss.

Perhaps it stems from the food industry, which goes out of its way to explain obesity as a consequence of a lack of exercise.

Wherever it comes from, the belief that weight is something you can simply burn off if you hit the gym hard enough is firmly entrenched in the gospel of public perception.

Truth be told, unless you make a living through exercise, for the average Joe or Jane, exercise is likely responsible for—at most—20 to 25 percent of their weight, leaving diet responsible for the lion's share.

While there is no behavior more conducive to good health than regular exercise, if weight's your concern, food is where it's at, and there are two incredibly straightforward things you can do to help.

1. Keep a food diary. I do. In fact, I'm on my longest streak ever, at 550 days without missing an entry. It takes a few months to get good at, but once you're there, it'll take you fewer than five minutes of work a day; five minutes of work that clinical studies have proven will double your weight loss. You can keep food diaries old school with a pad and paper, or download one of the dozens of apps that'll do the math for you.

2. Cook from fresh, whole ingredients. Don't worry about low this or low that, just focus on transforming raw ingredients into homemade meals and you'll be playing it far safer than you would be by dining out or eating a highly processed, but healthy sounding meal.

At the end of the day, if weight's your concern, you're far better off spending time in your kitchen with a pen, than time in your gym with a barbell. And if "because I exercised" really translated well, the gyms that fill up in January wouldn't be empty by March.

Hungry for more? Write to eatandrun@usnews.com with your questions, concerns, and feedback.

Yoni Freedhoff, MD, is an assistant professor of family medicine at the University of Ottawa, where he's the founder and medical director of the Bariatric Medical Institute—dedicated to non-surgical weight management since 2004. Dr. Freedhoff sounds off daily on his award-winning blog, Weighty Matters, and is also easily reachable on Twitter. Dr. Freedhoff's latest book Why Diets Fail and How to Make Yours Work will be published by Simon & Schuster's Free Press in April 2013.