In Black-and-White
If you want to know why your diet isn't working, trainer Jim Karas says keep a diary of every single random snack, licked spoon, broken cookie and (oops!) 1,000-calorie meal.

Jim says this works for a few key reasons. First of all, you see the data. "So many people over the years have said to me, 'I really don't eat that much; I don't know why I've gained so much weight," Jim says. "But when they start keeping a food diary, the reality of what they're putting in their mouths—the sheer volume of what was previously inhaled unconsciously—is right there in black-and-white. It's astonishing, it's enlightening, and it's indisputable.

Normally you might not think twice about, say, nibbling a sample of cheese at the grocery store or finishing the French fries on your child's plate. But if you're recording every morsel that passes between your lips, you're more likely to hesitate. "Oh, if I eat it, I have to write it down. Well, then, forget it. I'm not even hungry."

That self-policing is a huge help, since all those little tastes really add up.

Sticking to the Plan
If you journal, you'll stick to the plan.

The first few weeks on a diet are the honeymoon period. Then you start to lose focus and cheat a little here and there because you think, What the heck, I've been good. Before you know it, you've slipped back into old eating habits, and it's all over between you and weight loss.

But when you're dedicated to writing down what you eat, the honeymoon segues into a long and lasting relationship with healthy eating.

The Medical Evidence
Here's the medical evidence. According to a study in The New England Journal of Medicine, people who jotted down what they ate realized that they had been underestimating their daily intake by about 1,050 calories. No, that is not a typo. Added to your daily menu, 1,050 calories will put on an extra pound every three and a half days.

Researchers at the Center for Behavioral Medicine in Chicago found that when overweight people were asked to keep food diaries for 10 weeks, the most diligent recorders lost more weight than the lax ones. The study, published in Health Psychology, showed that subjects gained about 500 percent more weight per week than usual over the Thanksgiving, Christmas and New Year's holidays—with the exception of those who were consistent food diarists. As this group entered the dangerous season to be jolly, they began keeping notes even more faithfully than before. Instead of gaining weight, they actually lost, on average, about 10 pounds more than the others.

Even if you have a hard time keeping track of details and can't imagine recording every bite for the rest of your eating life, doing so for a short time could give you a jump-start on weight loss. A study in Obesity Research showed that regardless of how carefully subjects kept their food diaries, they dropped much more weight during their two most consistent weeks of note-taking than their least.

What You Should Record
You decide how much information to include in your daily confessional. The process can be as simple as writing down the type of food you eat and how much. But the abridged version—"burger for lunch"—doesn't cut it if you've actually devoured a quarter-pounder with cheese, mayo and ketchup on a bun, shared a bag of chips with your friend, and had several sips of his chocolate milk shake.

You may also find it helpful to keep a tally of calorie counts, especially if you try a diary and it doesn't seem to help with weight loss. Other data to consider recording:

  • the time you ate
  • what was going on
  • who you were with
  • how you felt afterward

This information can help you see when and why you eat, and then to break destructive patterns. Some people also log their daily weight and the exercise they get.