In The Bible
Just joking. I can't remember the exact gist of it, but you remember your HS Biology where they filled a glass to the brim with water and then told you to see how much sugar you could put in it without it flowing over. It was quite a bit. Anyway the explanation I heard had something to do with the blood volume and the amount that could be absorbed before the circulatory system became saturated. They didn't figure in the carbs, or fats though. It all sounded kind of hokey to me.
If it were me I would have said 50-60 grams. And got that rumor going. That way the supplement manufacturers could sell more protein. And I'd be trashing beef, chicken, fish, eggs, etc. Bad, bad, protein.
Causes intestinal polyps due to malabsorption. Get the picture.
This whole thing about protein absorption is a lot of bunk. Look at the length of the small intestine. Now they say that if I take more than 30 grams it's wasted. Where does it go? Does it sneak out of the system by magic. I figure it just stays in the small intestine and when there is a shortage in the blood it enters.
We're not like chickens. They feed them so much protein that some of it never gets digested. They were remixing it with their feed and sending it back through them. There was some big controversy with that so they started selling the 'chicken shit' to the cattle ranchers to mix with their feed.