Anecdotal and YMMV but my coach had me switch to a variant of the ketogenic diet (high fat, moderate protein, low carbs) and I saw solid gains in 6 months. Body fat dropped 4% (12 to 9) and I gained 5kg in muscle and hit PBs in the gym and on the bike. I don't know of its sustainability as it was *really* hard monitoring it, but it's something to look into.
In the end, Carleton summed it up when he said the final stage is figuring out what works for you.