There are several books dedicated to using bentos for weight loss. I have quite a few of them, and most have a lot of good ideas. I only got Yaseru Obento Recipe recently, but it's already become my favorite bento-for-weight-loss book and one of my favorite bento books of any kind. It is in Japanese only, as are all good bento books unfortunately. But it's so full of great photos and illustrations that I think you could get a lot out of it even if you don't read Japanese.

Yaseru Obento Recipe just means "slimming bento recipes". The subtitle is kirei de oishii baransu bento ga atto iu ma ni dekiagari! dakara nagatsuzuki shite reboundo nashi! That's a bit long, but it means generally "beautiful and delicious balanced bentos that are made in a jiffy! So you can keep (making them) for a long time, and won't have a relapse!" That sounds good to me, and the book does deliver on that promise.

Not only does it have a lot of delicious and great looking recipes, it has a lot of helpful ideas, from how to balance flavors, colors and nutrition in your bento to how to keep your bento safe to eat. The calorie target for each bento presented is 500 calories - the target for my bentos is 500-600 calories, so that fits me perfectly. Their formula to come up with the 500 calorie is broken down like this:

• 250 calories for the main carb - rice or bread. The most used carbs for a Japanese bento are white rice and soft butter rolls, so their calculation is 1/2 of a typical bento box filled with rice, or 2 small rolls. (I aim for a little bit lower carb figure, around 200, and try to use brown rice whenever possible.)
• 150 calories for the protein.
• 100 calories for other things - vegetables, potatoes, fruit, etc. They also aim for at least 100g of vegetables in the bento, with the goal of eating at least 350g of vegetables in total throughout the day.

Yaseru Obento Recipe is available from YesAsia or from Amazon Japan. Highly recommended!