A food and exercise diary is one of the most powerful proven aids for dieting and weight control. If you really want to lose weight and keep it off, writing down your calorie ins and outs is essential. Research shows that dieters who maintain a food and exercise diary not only lose more weight – they keep it off too.

Take a bag of M&Ms, for example. If you put it in your desk drawer at work, or on the kitchen bench at home, and snack on a handful now and then throughout the day, you hardly notice you’re eating them, do you? But if you take that bag, read the nutritional information (a 3 oz bag has about 450 calories), write down the calorie and fat content, and then sit in front of the mirror and eat the whole thing without stopping, it feels a bit different, doesn’t it?

Think of your diary as a kind of mirror. A mirror gives you a way in which to see yourself that you could otherwise only guess at. Of course, you probably don’t always like what you see in the mirror (and most of us would be much happier without one) but it is a useful tool. A food and exercise diary works in the same way as a mirror, providing you with a visual portrayal of what you’ve eaten. Instead of "guesstimating" how many calories you’ve packed in and burned off during the day (and let’s face it, when you do that it’s never a very accurate guess) you get to see the real calorie cost. That bag of M&Ms becomes 450 calories, instead of just an “insignificant” snack.

Recording your food and exercise habits jolts you into realizing how much you actually eat and drink each day and whether you are exercising enough. If you’re keeping to your recommended daily calories, seeing proof of that in your diary is encouraging. Most diaries will also provide you with a place to record body measurements, and it’s great to see these changing for the better as you follow your meal plans and exercise goals. If you’re slipping into old habits that are certain to pack the pounds on, seeing it in writing really hits home and should motivate you to get back on track. The diary also helps you develop greater self-discipline. You think twice about over-indulging when you have to record it – especially if you arrange for someone to check your diary regularly.

Keeping a food and exercise diary can also help you to spot patterns of behavior or habits that lead to excessive eating, and to identify the moods, situations, events, and people that trigger overeating. For some, this awareness is enough to encourage habit changes that lead to weight loss.

And finally, using a food and exercise diary not only helps you, it helps those who are helping you. Your physician, dietitian or counselor can use what you have recorded to assess your progress and make recommendations.