Have you ever tried tracking calories, not necessarily with the intention of hitting a goal? If not, the data can be rather informative, and doesn't necessarily match intuition. There's free apps like MyFitnessPal that makes it pretty easy. When I have done it, I've been able to correlate weight gain and loss to caloric intake. There are a few pounds of fluctuation from things like water retention and amount of food in your gut of course, but it's visible over the timespan of a week. If you eat a very consistent diet, you can measure differences on a scale across a few days.