This really is a loaded question and as such the answer could go in either direction.
Meaning you could gain weight with Casein, if that is your goal, although there are easier and more efficient ways of doing so, or you can take Casein protein and get ripped.
So it really depends on what you’re hoping to achieve by using Casein protein.
Like any type of food that you ingest, they all have a caloric value associated with it, which means that the more of it you consume over a given period, it can either put you in a calorie surplus or you remain in a calorie deficit.
Which simply means, if you eat more than your body requires, then you will store the unused energy as fat, however if you eat less than what your body requires, then your body will burn your fat stores as it’s energy.
Therefore, if your goal is to gain weight, you need to eat a surplus amount of calories, but if your goal is to burn fat, then you need to eat less than your body requires.
If you’re consuming more calories than you burn, then you will gain weight. So if you added Casein protein to make up your protein requirements for the day, but doing so puts you in a caloric surplus, then you will gain weight.
If your goal is to gain weight, then there are a lot of other protein powders that will help you to achieve this goal a lot faster and more efficiently than Casein protein.
Casein is usually a type of protein you consume at night last thing before you hit the hay or in between meals.
It’s designed to slowly release amino acids throughout the night so that they help repair your muscle tissue while you sleep.
So the idea is that you can add Casein to you total macros for the day, but just be sure that you don’t go over your calorie requirement.