Let's take a step back and understand some basics about nutrition as it relates to exercise. I'll cover the popular memes and then try to apply them to your situation.
- More muscle mass burns more calories. This is true, but it is only part of the picture. I'll expound on this a little more later on.
- Protein is more thermogenic. Thermogenic means it requires more Calories to process. And yes, protein has a higher Thermic Effect of Food (TEF) than either carbs or fat.
- You can't lose weight if you don't eat less. Basic principle is that if you consume fewer calories than you burn you will loose weight. Where that weight comes from is a function of diet and exercise. And keep in mind the adjustments have to be within reason here.
Now, before I go any further, I do want to call out that there are two major classes of protein shake mixes: mass gainers and simple protein. Mass gainers have a higher carb content and more calories, and are designed to make you gain weight. Whey protein and creatine supplements only contain enough extra to provide some palatable flavoring, but are largely protein. So when you are trying to lose fat, go for the simple proteins. Everything from this point forward simply has to do with the macronutrients. Whether you get them from protein shakes, food, or injection; it does not matter.
How do we get more muscle mass?
Our bodies respond to stress by making physiological changes so that it can handle that stress better the next time. That's how the flu shot and other inoculations work. The same goes for building muscle mass. You have to provide stress in the form of exercise to tell the body that it needs to get ready for heavier work. You then need to provide the body the nutrients it needs to build the muscle and help with recovery. It's a two step process.
It's great that you are swimming 30m a day 5 days a week. The problem is your body will only adapt to the point it needs to handle the stress you are putting it under. Unless you do something to intensify the work you are doing, the body will simply maintain. Weightlifters do this easily by adding more weight on the bar, or doing more volume. As a swimmer you have a few options: try to get more laps in the same amount of time (increase intensity), or increase the amount of time you are working (increase effort). It takes bigger muscles to be able to sprint effectively, so shaving off seconds from your lap time will help in this situation. If you hit a speed wall, supplement the swimming with some strength training to build up weak points, or overall strength.
The other part is you need enough protein to sustain your muscle plus extra so that your body can use that to build bigger/stronger muscles. For sedentary people, about .5g protein per pound lean body mass is sufficient to maintain the amount of muscle they have. Which means if you want to build muscle mass you need more than that. How much more will be in the next section. On top of that your muscles need energy for recovery. Fortunately they don't care whether that energy comes from carbs or fat.
Protein: little do good, heap do plenty
First, if you have renal (kidney) problems, you have to limit the amount of protein you eat. The kidneys do the bulk of the protein processing, and if they are not healthy you can overtax them if you are not careful. Healthy people don't have this problem.
You have a couple of strategies for protein intake if you are not trying to do the bare minimum to maintain the mass you have. Go for 1g protein per pound total body weight which will be more than enough to increase muscle mass, provided you are increasing the intensity of your exercise. Or you can go for the higher TEF of protein itself, and aim for 30% of your Calories coming from protein.
The macronutrients have the following amount of Calories per gram:
- Protein: 4 Cal/g
- Carbohydrates: 4 Cal/g
- Fat: 9 Cal/g
You can divide up the remaining Calories how you like. Any more than this, and you are reaching the law of diminishing returns. Now, if you take in very little carbohydrates, you can induce ketosis. With the elevated protein intake, your muscles will be fine.
Last parting shot: when you have a higher protein intake, the excess protein can start leeching calcium from your bones. You may need to supplement your Calcium while on a high protein diet.
Eat fewer Calories
Last but not least, you will need to eat fewer Calories than your burn to lose weight. If you want that weight to be predominately fat, keep your protein intake higher. However, don't overdo the calorie deficit, as that can backfire in a big way.
The best approach is to adjust your Calorie intake by 10-20% until the scale is moving in the direction you want. As long as your exercise is spot on, you are eating good food, and have the proper nutritional balance, the fat will come off.