What the P-ratio captures
The partitioning ratio, or P-ratio, describes how a change in body weight splits between lean tissue and fat. Defined as the change in lean mass divided by the total change in mass, a higher P-ratio in a surplus means more of the gain is muscle, and in a deficit a favorable ratio means more of the loss is fat with less lean tissue sacrificed.
It is a way of asking not just how much weight moved but what kind of tissue moved, which matters far more for body composition than the scale alone.
What nudges the ratio
Higher protein intake and resistance training push the ratio toward lean in both directions. Starting body fat also matters: more stored fat tends to favor fat loss over lean loss in a deficit. Genetics, training status, sleep, and the size of the surplus or deficit all influence the outcome.
P-ratio is a useful concept rather than a precisely controllable dial, and individual results vary widely. This is general educational information, not medical or training advice.