Subbing a protien powder for the MRP should be fine, an MRP has more carb content than a protien powder alone but I don’t think it will make that big of a difference as long as you are horking down tons of chanko all day. I was successful using this diet and I only used plain old protien powder myself. It’s a good diet for people that haven’t ever done the super scrutinized diet calculations that some of the other diets call for. I changed a few other things as well. The chanko recipe he came up with was too bland and boring for me so I used sweet corn and sweet peas instead of just corn, and I switched out the tuna with canned salmon ‘fillets’ (kirklands brand at costco, it’s just meat, no bones) and roasted chicken breasts that I had brined ala rumbochs recomendation in the ‘chef’s step up’ thread. Oh yah, and throw in a couple of chicken buillion cubes, and sprinkle some Mollymcbutterworths powdered butter stuff in when you cook your rice. Makes it alot more palatable. I also ended up measuring and calculating the total calories etc so I could be a little more “scientific” and the diet worked great. It is kinda boring, but the simplicity was hard to beat. Good luck packing on the muscle!