The only way to be sure you're eating fewer calories than your body burns is to know exactly what you're eating (and how many calories your body burns at rest). And the only way to know exactly what you're eating is to keep track of it.
This is especially true when you are just starting out on your road to losing weight. Your internal, "gut feeling", of how much to eat is out of balance - writing down what you eat and paying close attention to it will help you re-calibrate your gut feeling.
It doesn't matter what format you use; it only matters that you know, with absolute certainty, that you've eaten fewer calories than your target number.
Here are a few types / options to consider:
Spiral ring notebook. It's a little old fashioned, but it still works great. Boot-up time is zero; just open it and start writing.
Computer program. Your computer may not be portable and always at your side, but if you sit in an office all day this can be a great place to keep your food journal.
Spreadsheets, word processing programs, or a note taking application like Evernote or Onenote all work equally well.
Many of these programs are easy to integrate with your phone, so you can use your phone as well as your computer.
Smartphone app. Your phone is always with you, just waiting to do your bidding. You can input the details of your lunch as soon as you've finished eating, wherever your are.
Most of the apps I've sampled also come with a food-lookup option, so you can determine how many calories your lunch had from within the app itself.
Many of the apps have online access as well, so you can view and edit your food journal from your computer, and keep track of your history, from that larger screen in your office.
There are many different methods you can use to keep track of what you're eating. It doesn't matter which one you use, only that you use one.
Can you splurge a little bit at dinner, or have a brownie for dessert? Guessing at the answer could be the difference between losing weight and not.
- Chris Butterworth