If you want to lose weight, there’s one powerful tool that should be added to your weight loss arsenal. It’s not a new diet pill, supplement or fad diet. It’s a food diary.

Keeping a food diary can double your weight loss according to a new study from Kaiser Permanente’s Center for Health Research. “The more food records people kept, the more weight they lost,” said lead author Jack Hollis Ph.D., a researcher at Kaiser’s research center in Portland, Ore. “Those who kept daily food records lost twice as much weight as those who kept no records. It seems that the simple act of writing down what you eat encourages people to consume fewer calories.”

A food diary provides both a record of what you’re consuming and a way to hold yourself accountable. Looking at what you’ve eaten over the course of a day or whole week can pinpoint areas where you need to cut back or improve. But the diary can also help you track your progress and successes. Seeing your progress in written form can be a powerful motivator and incentive to continue your weight loss efforts.

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“Journaling felt weird at first — I had a hard time even remembering what I had eaten by the end of each day — but after just one month of telling all to my food diary, I had dropped five pounds,” said Anita Hamiliton, writing in her Time Magazine blog. Anita wasn’t part of the Kaiser study, but found keeping a food diary “worked like a charm” when “sheer willpower and daily exercise had failed.”

Participants in the Kaiser study also turned their food diaries in at weekly support meetings, followed the heart healthy DASH diet which promotes lots of fruits and vegetables and low-fat or non-fat dairy, and exercised for at least 30 minutes each day. The study was one of the few trials to include a large percentage of African American participants. African Americans have a hightler risk of overweight, diabetes and heart disease.

You don’t have to be a part of a formal weight loss program to benefit from keeping a food diary. Scribbling down what you eat on a Post-it note, sending yourself an email tallying each meal are also good ways to track what you eat, researchers say. There are a number of websites that allow you to create your own food diaries, such as myfooddiary.com or thedailyplate.com.

Do you keep a food diary? What did you eat today? Leave  your response in the comments section below.