It's actually possible, while complicated, to figure out close to the exact number of kcal used.    While at a deficit (per g):  Protein ~3.4cal. Fiber ~1.9 cal, carbs=4 fat=9 The harder part is figuring out how many calories you burned.  Lifting weights at 20% efficiency is not exactly (weight lifted)/(0.20), if   6b13  you include the effect of recovery burning extra kcals.    But seriously, it's missing the forest for the the trees.  Eat less if you're fat and you'll lose weight