Whey protein is absorbed very quickly by the body and leaves you hungry in a short amount of time. This is never ideal as a meal replacement as ideally, you want a slow-releasing protein that keeps you full for long periods. Meals should satiate you for up to four to six hours with no snacking in between. This goes hand in hand with the point about hormones above. When you control your blood sugar spikes, you manage your insulin release and therefore better control your food cravings, your moods and your ability to look good naked.