I use shakes as a meal replacement and also lift weights to build muscle in addition to cycling and I think I probably add 25 to 35 grams of protein to my shakes with whey protein powder(the higher end after weight training the lower end otherwise). You can also use milk or other types of protein powders.While the right amount for you will depend on a number of factors such as your size, training style or whether its a post/pre training drink etc. I think 25 grams may be a good number to shoot for particularly if your concern about the amount now.For a complete ingredient list of my shakes see the post-training recovery drink thread but note I cycle the fats as well with more post ride .