Everyone claims to have a simple way to lose weight. But this one may actually work: Keep a food diary.

It turns out dieters do a lot better by simply jotting down what they eat. No pills, no surgery, no cost -- just paper and pencil, and a little honesty.

Researchers at Kaiser Permanente studied 1,700 people and found those who wrote down what they ate lost twice as much as those who didn't.

"You know, what did you like the least and they would say, 'well I don't like keeping food records,' and we'd say 'what helped you the most?' and they'd say 'keeping food records,'" said Senior Researcher Victor Stevens

The diary keepers lost an average of 13 pounds over 6 months.

"And a lot of us go through the day on auto-pilot. You write it down then you're not on autopilot anymore."

Julie Satterwhite learned that first hand. At age 47, she's struggled with her weight for years. She kept her food diary religiously. It worked. She lost 30 pounds in 6 months.

"So if I were walking through the kitchen and the kids had brownies on the counter, I would have to think about do I want to write that down?"

So give it a try. Writing it down may help you slim down.