What you are thinking about is the TEF (thermic effect of feeding). It is with protein than it is with carb or fat
Once again as shown with ONL or FUNL people with higher p-ratio see more loss of nitrogen. It might make more sense if you understand what happens when measuring ONL. Below is an excerpt
from Protein Essentials (Hale 2007)
Obligatory protein requirements
The obligatory protein requirement is the amount of protein necessary to keep a person in nitrogen balance on a daily basis (of course this could change according to activity levels or other stresses). This requirement is determined by measuring nitrogen excretion while an individual is consuming a protein-free diet. Since nitrogen consumption is zero, all nitrogen excretion must be coming from body proteins. When measuring this value, the diet must be adequate in calories and carbohydrate intake.
The obligatory protein requirement has been estimated to be approximately 50–60 mg/kg per day, meaning a 100 kg person would lose 5–6 grams of nitrogen per day. Since protein is approximately 16 percent nitrogen, a loss of 5–6 grams would indicate a loss of 33 grams of protein per day. Taking into account digestibility issues and individual variance, a safety factor has been added to the value. This is the basis for the recommended daily allowance (RDA) for protein which comes out to 0.8 g/kg per day, which should be sufficient for 95 percent of the population to maintain nitrogen balance. The RDA assumes high quality protein intake and adequate energy consumption. RDA values can also vary between age groups. Another thing to consider is that RDA values were never meant to be applied to active individuals (much less bodybuilders and competitive athletes).
thanks,
Coach Hale
www.maxcondition.com