Every few years, another dietary fad sweeps the country. If you do this one big thing—say, eat fewer carbohydrates or fill up on protein—you’ll be healthier and thinner.

But in real life, healthful eating depends on the dozens (if not hundreds) of small decisions that you make every day…assuming that you even make decisions. Most people eat without thinking, nibbling at leftovers as you store them after dinner…grabbing a snack when rushing out the door…or taking a few quick swigs of a soft drink.

How many healthy (or unhealthy) foods do you actually consume? You probably don’t have a clue. The only way to know for sure is to write down everything you eat.

Compelling research: People who keep a food journal lose weight at twice the rate as those who don’t keep track, according to a study published in American Journal of Preventive Medicine. 

In addition to raising your awareness to what and how much you’re eating, a food diary makes you aware of your habits—which can ultimately help you change your behavior and make healthier food choices so that you eat less of the wrong foods and more of the right foods.

FIND YOUR EATING STYLE

It might seem like a hassle to keep a food diary. But you don’t have to do it forever…a month is usually long enough. And it’s an extremely powerful tool for changing behavior. In fact, it’s the best way to identify your eating patterns. Nutritionists have discovered a few main patterns that define an individual’s eating style. For example…

“See food” eaters might cook healthy, well-balanced meals but still consume hundreds of unnecessary (or unhealthy) calories by eating whatever appears in front of them—doughnuts at the office…sugar next to the coffee maker…soda in the refrigerator, etc.

Emotional eaters turn to food whenever they feel extra-stressed.

Mindless eaters grab food on the run because they’re often too busy or harried to enjoy leisurely meals.

You can easily consume 1,000 extra calories a day without even thinking about it. Some people are aware of their eating patterns, but many never realize where the bulk of their calories comes from.

A food diary—including a “cheat” diary (see below) to account for the dozens of quick, mindless bites that you probably take every day—will help you identify your eating patterns…where your calories are coming from…and the quality of your diet. Are you getting enough antioxidants and fiber? Are you overloading on sugar? Writing it down is the only way to really know.

KEEP IT SIMPLE

One month is the recommended length of time to keep a food diary because that’s about how long it takes people to change their habits. One of my clients, a busy hedge-fund manager, soon realized that he would munch mindlessly on junk food. After recording all of these “cheats” for six days, he realized that he needed to think before snacking. (He went on to lose 20 pounds over the next two months.)

The four pillars: A food journal only needs to include four basic pieces of information—what you ate…how much…the food group (fruits…grains…vegetables…meats and alternatives…and dairy)…and how you prepared it. The details are important because people tend to engage in what’s known as “perception deception.” You may see yourself as an active, healthy person and discount aspects of your behavior that don’t align with your self-image.

Example: You may think that you’re eating a healthful diet because you include a whole grain with every meal, but what if you only take a bite or two of brown rice and a double-helping of steak…or the broccoli that you sauté is swimming in butter? Details matter!

JUST A FEW MINUTES A DAY

I advise clients to make diary notes every time they eat, if possible. You’ll forget things if you wait until the end of the day…and jotting down an entire day’s notes can make it feel like too much work.

If you’re comfortable with computers/phone apps (MyFitnessPal is a popular app), there are dozens of programs for tracking calories, food groups and portion sizes. But it’s just as easy to carry a pen and a notebook…or send yourself a simple text or an e-mail. After you’ve done it for a few days, it almost becomes automatic.

A pre-diary is good for those who are really committed to improving their diets…and for planners who prefer not to do things on the fly. Every day, write down what you plan to eat—the food groups, the portion sizes, preparation methods, etc. You can use the same diary (using a different-colored pen) to write down what you actually ate.

A cheat diary is one of the most helpful tools. The calories and unhealthful ingredients from foods that you mindlessly pop into your mouth can add up fast. Especially for people who are too busy to keep a more detailed diary, a cheat diary is a good way to become aware of the unhealthy food choices.

Focus on portions. Research has shown that people underestimate how much they eat and drink. They often don’t realize that today’s supersized portions have far more calories than they imagine.

Example: When I asked students in an introductory nutrition class how many calories were in an eight-ounce serving of a popular soda compared with the calories in a 64-ounce “double gulp,” 70% underestimated the proportional increase. (An eight-ounce serving has 100 calories, and a 64-ounce soda contains 800…but most students estimated that the larger beverage only had 300 calories!)

Larger portion sizes may have started in restaurants/packaged foods, but now they’re also a problem at home. You need to know how much you’re eating—not how much you think you’re eating. I advise everyone to buy stackable measuring cups and spoons. You can also buy dishware that marks off serving sizes and even wineglasses with fill lines (the standard serving size is five ounces).

Weigh your foods. A kitchen scale (like the EatSmart Precision Pro Digital Kitchen Scale, among many others) is a great way to know exactly how much, say, a four-ounce serving really is. After using a scale for a while, most people learn to “eyeball” portions with decent accuracy.