This depends entirely on your maximum protein requirement per day. Average individuals need about 0.8 grams per kilogram of body weight. However, athletes need about 1.3 to 1.8 grams per kilogram of body weight. This is because they experience workouts that require protein to allow the muscles to recover. Average people only take 1 protein shake a day when they exercise, because they already get enough protein with their normal diet. Athletes sometimes go up to 2 shakes a day, because they need to consume more protein than their regular diet can provide.