My rationale is as follows:
1. Studies have routinely shown that the body gets near-maximum benefit from 20 grams of protein. When greater amounts of protein are consumed, the remainder is mostly burned for energy or excreted, not used for structural needs.
2. It appears that it takes the muscles around three hours to “cool down” from a protein feeding. The science is still in the works on this one, but it’s doubtful that the ultimate recommendation will wander far from this mark. Plus, three hours is a reasonable amount of time to space a meal.
3. Assuming you sleep an average of eight hours, you have sixteen other hours during which to eat. If you perfectly spaced your meals, you could eat six times. Most of us will fall short of this, but five meals is easily achievable and will provide nearly the same benefit.
If you do the calculations, you’ll find that the “mostly reasonable” weight-based recommendations all wind up somewhere in the vicinity of 90-140 grams of protein per day unless you are either much lighter or heavier than the average person. Thus, I often call these figures “accidentally correct,” because they are good recommendations, they’re just more complicated than they need to be.