
Originally Posted by
Damienm05
Well, let me clear something up first and foremost. Eating a lot of calories but not having a high intake of lean meat and other protein sources, you can still make big gains. I mean, if you were to eat 5000 calories a day from mainly carb sources, nuts, and such - there'd be 200g of protein in there somewhere. So yes, you'd get fat due to the composition of your calories in part but composition aside, the calories would be a larger issue.
With that said, we can use the same logic towards your question. Your calories are comprised mainly of lean protein, which is the building material for all active mass on your body, however, due to the fact that your calories are so low - you will only lose muscle mass. This is largely because, since you're not consuming energy sources (carbs/fats), that protein will end up being converted to glycogen in a long and far less efficient process called gluconeogenisis. In terms of preference for fuel, the body wants simple carbs to burn first, complex carbs sustained, fats, and then finally, only when needed, protein. So, when this last resort comes into effect, none of that protein will be available for muscle recovery - it will simply be converted. Thus, you end up with a far efficient system for creating energy to fuel you workouts, the amino acids aren't readily available for repairing the lean tissue damaged during said workouts, and you're hindering you bodily functions without enough carbs and fats to fuel brain function, decrease inflammation, lubricate the digestive tract, etc. I could go on forever.
To directly answer your question using the example of 1500 calories with 300g of protein - You'd lose body fat, muscle, energy, and largely reduce metabolic capabilities. Protein only dieting is a big no-no in this game and that's why keto diets exist. If it's an interesting concept to you, do a search on them.