Anyone who wants to gain muscle needs to be eating adequate protein for the purpose, especially foods containing branched-chain amino acids, which are necessary for muscle growth, as I understand it. The three essential BCAA’s are leucine, valine, and iso-leucine. If you don’t get enough of them, you can’t put on muscle. (Again, as I understand it.)
As for the need for insulin, IGF1 and HGH can do an adequate job of promoting muscle growth, I don’t see the need for exogenous insulin. Furthermore, protein stimulates insulin secretion, though at half the rate at which carbohydrate does, so I suspect that eating enough protein should raise insulin enough for anyone’s purpose. Remember that raising insulin too high causes fat storage and stuffs the muscles with glycogen.
The muscles may look larger if full of glycogen, but one good workout should take care of that. My concern would be adding unwanted adipose tissue, as I don’t like the look of that layer of fat that even the leanest athletes seem to have these days.
ETA: Don’t forget that the reason fat and carbohydrate can’t build muscle tissue is that they don’t contain any nitrogen. Only proteins/amino acids contain nitrogen.