Question: Should I take 3 grams of leucine per meal?
Leucine is metabolized into a leucine metabolite that is the signal of protein synthesis. It's the thing that tells your muscles whether they should be synthesizing protein. But do you synthesize more protein when you upregulate all the factors of muscle protein synthesis? Well, that is entirely dependent on the amount of amino acids you have supplied. Think about it this way. Why is leucine used as the marker to determine how much muscle protein to make? Because usually when you get leucine, it's with high-quality protein that has all the other amino acids that you need to make muscle protein.
Now, the question is, is meat better than isolated protein? The research is pointing in the direction that at least some whole foods are just better than protein supplements, number one. Perhaps as a general principle, perhaps whole protein foods are better than protein supplements, number two. Number three, taking leucine or the leucine metabolite that regulates muscle protein synthesis is not going to be better than getting whole proteins even from protein supplements when you get enough protein to provide that leucine because the leucine and its metabolite don't actually achieve peak muscle protein synthesis unless you supply the protein with it. If you supply the protein with it, you do get the leucine.
There probably are questions that can still be worked out about this, but it's probably going to wind up being that it's a waste of time to take the leucine if you're getting enough protein, and it's stupid to take the leucine and not get enough protein. You should just eat a lot of protein is where I think this is going.