I’ve weighed in again this morning with my new-fangled fat tracking device and high-capacity scale. I’m down another 3 lbs and 2% body fat from last Monday. During my workout this morning I was thinking about the relevance of the latter.

If the fat percentage had been constant while I lost weight, that would indicate that I lost an equal amount of fat and non-fat. Since it wasn’t constant, I wondered how much non-fat I gained to offset that fat loss. To answer this question, I enlisted the skills of my friend Cygnus:

Given that last week I weighed 350 lbs and my body fat ratio was 42.1% and that this week I weigh 347 lbs and my body fat ratio is 40.1%, how much fat vs. non-fat did I gain/lose? Assume, for the sake of having a workable algorithm, that the only weight lost was fat and the only weight gained was non-fat (muscle, etc).

In less than minute he kicks me an answer—I’ve dropped 8.20 lbs of fat and gained 5.20 lbs of non-fat (muscle, etc).