A decade-plus ago, I hiked the Fish River Canyon in Namibia, and one of my hiking companions used only supplements over the 5 days or so, no "real" food. He managed fine--much better than I'd have done on the same diet. Mind you, he had about 25 or 30 years on me, and aside from the initial descent and final climb, there were no serious grades.
No specific advice on shake, Ian, but I've attached a recipe for making energy bars. This has a good base of carbs, some mono-unsaturated fat, and a good dose of protein, too. No idea what the total calories might be, per unit, but I find that a square of this, about 2 1/2" square and 1"-plus thick, is an excellent snack midway through a 3- or 4-hour ride.
The recipe is simple and quick, and you can adapt it to your taste. I got the original from a sometime contributor on crazyguy, and I've added my own notes (yellow-highlighted for my use). As an example: I use almond butter, rather than the peanut butter in the original. I prefer the taste of almond butter, and peanuts make me burp.
Have also added a note on a shake/smoothie from another crazyguy post, but I haven't tried this, so can offer no opinion on it.
Hope that's useful,
Cheers, John
