What you read is partially true. Following a high protein diet will prevent muscle loss when on a low calorie diet. The protein doesn't have to come from casein however. It come from whey, eggs, lean poultry, fish etc.
It's very important to set up your fat loss diet with the proper macronutrients so you loose fat and not a combination of muscle and fat.
Check out this video I made on how to calculate your calorie, protein, fat and carb intake based on your goals ->
https://www.evolutionary.org/forums...s/nutrition-101-carbs-proteins-fat-46427.html
A rough estimate to determine how many calories you need is to multiply your body weight (in pounds) by 15. That will give you the amount of calories needed to maintain your current body weight. If your goal is to gain weight, multiply your body weight by 17-18. If your goal is to loose weigh, multiply your body weight by 12-13.
For example, a 200 pound person would need 3000 calories to maintain his weight (200 x 15 = 3000).
Once you have determined your calorie needs. Set your protein intake. A good number to shoot for is:
1-1.5 grams of protein/pound of body weight for natural athletes
1.5-2grams of protein/pound of body weight for enhance athletes
Once you have set your protein intake, fill the rest of your calorie intake with carbohydrates and fat.