There's a lot of discussion (and some science) about the imperfect correlation between calorie consumption, calorie burn, and body weight, but I've found for my own body that the correlation is very clear and precise. Your experience sounds similar. It's amazing, isn't it, that if you add or subtract one small factor from habits that are otherwise quite steady, it makes a measurable difference.

For me, the problem is that I will always naturally tend to "eat up" my exercise (I bicycled daily for two years without losing a pound), so I have to apply controls at both ends of the process by tracking both burn and consumption.

Time to get back on that...