One of the primary health and nutritional advantages to skim milk is that it’s a good source of protein, specifically slow-digesting casein protein. Skim milk contains dozens of proteins, including casein and whey proteins (which make up around 20 percent of the protein in skim milk by weight.) Lactoglobulin is the most predominate whey protein in milk and skim milk products.

Casein protein, specifically casein protein micelles, are an interesting contrast to whey protein, especially for bodybuilders and people pursuing a resistance or weight training regimen. Unlike whey protein, which is digested very quickly by the body (in some cases in under 30 minutes), casein proteins in skim milk can take much longer for the body to break down and digest (some estimates say as long as 7-8 hours for casein to be fully-digested.)

While this might sound like a bad thing, it can actually be beneficial, especially if your goal is to make sure that your body has a constant supply of protein available post-workout for muscle recovery and growth.

Because casein has a longer digestion window than whey, skim milk is an excellent source of slow-digesting protein, especially before you go to bed. The slow digestion of casein proteins in skim milk will ensure that you remain in positive nitrogen balance (meaning you have sufficient protein available to the body) during the nighttime fast.

also just a tip, these are just supplements, most of you protein and carbs must come from your diet
eat eat eat