For six months, they kept food diaries and were encouraged to eat a healthy diet and be physically active. They also met weekly in groups to share their food diaries and brush up on skills like how to judge portion size.
After six months, participants had shed almost 13 pounds, on average. The most powerful predictor of their weight loss was how many days per week they kept their food diary, says Victor Stevens, PhD, senior investigator at the Kaiser Permanente Center for Health Research in Portland, Ore.
Those who kept food records six days a week -- jotting down everything they ate and drank on those days -- lost about twice as much weight as those who kept food records one day a week or less, Stevens tells WebMD.
Why Food Diaries Work
"I think the most powerful part is accountability and the next most powerful part is increasing awareness of where those extra calories are coming from," says Stevens.
Showing your food diary to someone else is even better, in terms of accountability; that's what participants in Stevens' study did. "You're accountable to yourself when you're writing it down and you're accountable to other people who are looking at your food record," says Stevens.
Food diaries can also help target areas for improvement. For instance, Stevens says a food diary might make someone realize that he or she is eating 1,000 calories at lunch and set a goal to trim lunches.
5 Tips for Keeping a Food Diary
Stevens offers this advice for keeping a food diary:
Write as you go. Don't wait until the end of the day to record what you ate and drank. "We recommend they write it down as soon as they can after they eat," says Stevens.
Focus on portion size. Practice at home with measuring cups, measuring spoons, or food scales. And be aware that people tend to underestimate how much food they're served.
Use whatever type of food diary works for you. It doesn't matter whether you use scrap paper, a personal digital assistant (PDA), or a notebook. What matters is that you use it, says Stevens.
Don't skip your indulgent days. "We encourage people to keep records especially on days when they're tempted to eat," says Stevens. "What gets measured tends to get changed."
Cook at home. You'll have more control over what you consume, and you know what that food contains, and how much of it you're eating. That makes for a more detailed entry in your food diary.
Also, remember that even modest weight loss -- even if it doesn't bring you down to your ideal weight -- may have health benefits, says Stevens.