• Mayo Clinic Minute: Lose weight with a food diary

If you're trying to lose weight, a food diary can be a valuable tool. Logging what and how much you eat can reveal forgotten calories and hidden patterns that may be thwarting your work to trim extra pounds.

Watch: The Mayo Clinic Minute

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If you're going to eat it, you should enter it in a food diary.

"This is your biggest tool," says Dr. Karen Grothe, a Mayo Clinic psychologist. "So it can be as simple as just writing down when you eat and what you eat. But, really, a more complete food diary would also include the serving size, the amount of calories."

Dr. Grothe says you'll probably be surprised by your calorie tally.

"We tend to underestimate what we eat by 50 percent if we're not actually measuring and writing it down."

A food diary can find that extra 50 percent and reveal patterns that create extra pounds.

"Maybe I'm not getting a lot of calories earlier in the day, and they're really loaded to the end of the day," says Dr. Grothe. "Maybe I'm getting a lot of calories in the evening or after dinner time."

You can start a simple food log with just pen and paper, or go higher tech with a new app. Either way, Dr. Grothe says try to make your diary entries as close to your meals as possible.

"Minimum of three days a week if you're trying to lose weight," says Dr. Grothe.

And every so often after you've reached your goal, stay accountable for what's really on the menu in your life.