I think the friction of reporting could be replaced with slicker access to information. For example, a taskbar or smartphone widget that tells you how many calories you have left to consume, some sort of UI giving you information as you are selecting a meal (rather than later during self-reporting), or emails/text messages when you go over your target.

Also, transparent information gathering could be useful for later investigations. For example, you might eat normally for two months and then analyze which calorie sources you'd be most willing to sacrifice.