I have a selective memory when it comes to food. Ask me what I ate this week, and I’ll tell you about a really great lunch I made or the world’s best slice of pizza I ate. What I probably won’t remember is the can of cashews I plowed through while watching a movie. Or the snack I had between lunch and dinner.

That’s where food journaling comes in. A 2008 study in the American Journal of Preventive Medicine found that the more food records people kept, the more weight they lost. “Many people are not aware of what they’re eating until they actually start writing it down,” says Laura Cipullo, RD, CDE, a registered dietitian and certified diabetes educator in New York City.

Admit it: You don’t count the number of chips you’re eating when you’re elbow-deep into a bag—or measure a cupful of pasta when you’re dishing out dinner. “The thing people are always shocked at is how much they ate at a restaurant,” says Kristin Kirkpatrick, MS, RD, LD, a registered dietitian and wellness manager of the Cleveland Clinic’s Lifestyle 180 program. “It’s going to be a large portion and have a ton of salt. [Journaling] just really increases awareness.”

Keeping a food journal is not just about weight loss or maintenance. It can also help with blood glucose control. By noting how the foods you eat—and that means all of the foods you eat—affect your blood glucose levels, you can alter your diet to avoid spikes. The cause of blood glucose increases is an individual thing (that’s why one person with diabetes can eat oatmeal and be fine while another goes too high), so learning what works for your body is critical.

Keep a journal long enough and you’ll be tuned in to your feelings of hunger and satisfaction levels, the emotional triggers that lead you to overeat, and how your blood glucose responds to different foods. How do you start a food journal? Read on for seven tips from the experts.

1. Choose your journal
Sounds easy enough, right? But there are more ways to keep a food journal than you might have thought. Sure, you could buy a typical journal with blank pages, but that doesn’t work for everyone. Since you’ll be keeping your journal with you all the time, you may want to pick a smaller, thinner notebook that can easily slip into a back pocket.

Those for whom longhand is the equivalent of carving letters into stone might pick a digital way of keeping track, like adding notes taken throughout the day to a food journal on their computer. Both Microsoft Word and Excel are great options, allowing you to format the journal as you please.

Or, if you want to keep your blood glucose log and food journal separate, look for an online version. Plenty of sites will not only help you track the food you eat but will also estimate calories, fat, carbohydrates, sodium, and other nutrition factors. Many include nutrition information from chain restaurants, which can give you a better idea of what you ate while dining out than a blind estimate can. Try MyPlate or Calorie King. (There are apps for those, too.)

Tech-savvy food journalers may opt to keep records close at hand—say, on a smart phone or a tablet like an iPad. The upside of this option is that you’ll probably always have your journal on you, even when you’re mindlessly munching. Cipullo’s top pick is the dLife Diabetes Companion iPhone app, an all-in-one diabetes tool that includes a searchable list of foods and time-stamps each entry automatically. Another great option is My Net Diary’s food diary. It runs on iPhones and iPads and, for a fee, Android and BlackBerry phones.

2. Write as you go
It may be more time consuming to keep records in “real time,” but the most helpful journals are used at mealtime, not the end of the day. “When you’re in the moment, you’re able to be more hands on and be able to say, ‘OK, I had x amount of this’ versus ‘Oh, I think I had such-and-such,’ ” says Robyn Goldberg, RD, a registered dietitian in private practice in Beverly Hills, Calif. “It helps a person ‘own’ what it is they ate versus guesstimating what they ate.”

People without diabetes can get away with journaling after a meal. But, Cipullo says, if you have diabetes, your journal should be out before you take a bite, too. “You need to take your blood sugar before the meal, and then you need to write that down,” she says. By keeping track of your premeal blood glucose levels, you can learn how different foods affect you.

3. Take notes…
You now have a journal and you know when to use it. The next step is—surprise—noting what you ate. The golden rule of food journaling is that if it passes your lips, you must write it down. Even the small stuff adds up, so no cheating.

How detailed you get when it comes to the foods you eat is up to you (and your dietitian), but more details are always better. Just make sure you’re not simply listing single foods: chicken, broccoli, milk, cereal, and so on. Instead, do your best to estimate the amount you ate. Ask yourself: Was it 3 ounces of chicken? A piece of steak the size of a deck of cards? How many ounces of soda or juice did you drink?

Of course, that doesn’t mean you need to literally measure food wherever you go. “I don’t think it’s realistic to walk around with a measuring cup, but you need to know what a serving of rice is,” says Kirkpatrick. For some foods, like cereal or anything else that has a food label, determining a serving size is as easy as reading the nutrition facts if you know what a cup and a half cup look like. But for meals you eat out, it can be harder to determine if you’re eating a cup of rice—or 5. (To learn some serving-size cues, go here.)

At a bare minimum, your food journal should include your premeal blood glucose number, what you ate and how much, the number of grams of carbohydrates, any diabetes medication you took, and your two-hour postmeal blood glucose level.

4. …and not just about food
Maintain a journal with the above information, and you’ll have better control of your diabetes and your weight. To see an even bigger change, you need to look beyond the food to how you feel before and after you eat in terms of hunger, satisfaction, and emotions.

An easy way to assess your hunger is to use what Goldberg calls a hunger-fullness scale: You rate your hunger from zero to 10—zero being after a fast and 10 being so full you feel sick. The number 1 (the rating for extreme hunger) scribbled next to each dinner entry indicates you need to eat a snack between lunch and dinner while a 9 (meaning you’re stuffed) next to every lunch indicates you need to stop earlier in the meal. Once you start picking up on these trends, you can work to change your habits.

Just as being hungry after a meal can lead to bingeing later on, feeling unsatisfied with what you ate can also make you eat more. Imagine you’ve been craving a hamburger for three days; you rank your satisfaction as low despite having felt full after every meal. A review of your food journal can show you that you’ve been overeating to make up for the satisfaction you’re missing by not indulging in a burger. Once you know that, you can take action, maybe by opting for a more healthful turkey burger instead.

Your emotions at a meal are also important. Most people are emotional eaters in some sense of the word, but it can be hard to pinpoint exactly what causes them to eat.  Maybe you polish off a giant slice of cake when you’re by yourself because of the shame you feel—but you barely touch that same cake when you’re around your judgmental sister. Identifying your emotions in your food journal and then recognizing them before a meal can help you avoid overeating. That helps keep weight and blood glucose levels down.

5. Review trends
A food journal is almost useless if you don’t review it. Only by looking over the past day, week, month, or longer will you start to spot trends in blood glucose, hunger, and satiety. There’s no right or wrong time to review your journal, though Cipullo says it’s ideal to review entries at the end of the day. To notice longer-term trends, she recommends reading it over on a weekly basis. Try to discover why you had a high blood glucose level instead of waiting until you get to the doctor or dietitian to find out.

Paging through journal entries can also show you the bigger picture of your diet, says Kirkpatrick. It can reveal whether you eat too many carbs or if your meals are severely lacking in the vegetable department. It may take some time to review, but it’s time well spent.

6. React
The beauty of keeping a food journal is that it gives you the opportunity to change the way you eat. Notice that you barely add vegetables to your meal? Make a point of eating more—and journal that, of course. Find out you snack too much, especially on high-carb foods? Take time to prepare snacks that you can eat throughout the day—and limit yourself to those. Says Cipullo: “You can see, ‘Oh, after breakfast my blood sugar was 180, so tomorrow I know I’m not going to have that [food]. I’m going to try decreasing the carbs and increasing the protein and see if that helps for the breakfast tomorrow.’ ”

7. Tell the truth
If you want to keep your blood glucose in control or lose weight, don’t lie. “The first goal is to definitely be honest,” says Kirkpatrick. “If you lie to your food journal, you’re just lying to yourself.” Sure, you can write that you ate 10 M&Ms instead of two bags, but it won’t do you any good. If you see a dietitian who reviews your journal and advises you based on it, you won’t receive the right feedback. And if you’re keeping the journal for yourself, you’ll just be wasting your own time.

“Make sure your heart is in it and you want to do it. You have to be ready. You need to say, ‘I need to make a change, and I’m going to do it,’ ” says Kirkpatrick. Once you’re fully committed to it, being truthful in your food journal may help you in surprising ways. “Some of my clients have said, ‘I really wanted that chocolate chip cookie, but I didn’t want to write it down.’ ” Even if your eyes are the only ones reviewing the entries, you can still hold yourself accountable for what you’re about to eat, what you already ate, and how that affected your body. And in the end, that’s what matters.