We normally go through a short fast everyday – during our sleep! When we sleep, we normally do not give our body the nutrients to recover ourselves like we do when we are awake. Because of this, it’s possible that you might lose a little bit of muscle mass each night! Now, this probably won’t be a lot of muscle mass, but over time it may add up.
On the other hand, you don’t want to have a big meal right before you go to sleep either because this may impede your sleep cycle during the night and not allow you to get into a very deep level of sleep. So, we have to find some sort of balance between eating a large meal so that we don’t get into a catabolic state and eating nothing so that we get a good night’s sleep.
What some people do before they go to sleep, myself included, is take some sort of slow digesting protein, like casein, before bedtime. I will normally eat cottage cheese or take a casein shake before bed, but I prefer cottage cheese. All dairy products’ protein is about 80% casein and 20% whey, and some studies have shown (and it is my opinion) that the mix of whey and casein is better than just pure casein. Since the whey digests faster, it produces a larger raise in insulin so that the protein will actually get into the muscles. Also, drinking milk is fine (insulin doesn’t really matter in the great scheme of things), but you might wake up to use the bathroom if you go that route.
Of course, if you don’t have cottage cheese (or just don’t like it), you could always mix casein with a little bit of whey before you go to bed. Also, you can really use any source of protein that you have avaliable to you, including chicken, tuna, beef, eggs, etc. Even thought cottage cheese is that “standard” night-time snack, the only real advantage that is has over the other sources is a little bit more leucine (one of the amino acids responsible for the initiation of protein synthesis) per gram of protein (due to the types of protein in dairy), but it really isn’t that big of a deal.
Whatever you decide to do, just realize that leaving your body with no nutrients all night long is a type of fast and can become catabolic in some situations. I recommend that you have some cottage cheese before bed as buying casein shakes can become pricey and, in my opinion, offers no further benefit and might not even be as good as the cottage cheese.
Edit: While many still advocate this advice, including myself, do not think that going through an acute fast is going to make your muscles fall off. As shown with intermittent fasting, having short periods of fasting can still be a great way to build a great body. However, even many people on an intermittent fasting diet still eat protein before they go to sleep. Having a slow digesting protein in your body trickling amino acids into your blood stream will not produce a lot of insulin and will possibly start the fast in a less catabolic state.