Protein is more than just used for muscle regeneration, it's one of the most important elements your body uses for life. It can be used for energy, but why use it when you can use fats. Sure some carbs are fine, and like I said 20% of my calorie intake comes from carbs.
However, digestion breaks proteins down to amino acids. If amino acids excceed that of the body's requirements, they are metabolised to either glycogen or fat and then used for energy production. If amino acids are going to be used for energy, they are converted to acetyl CoA which then leads to the Krebs cycle for oxidation, producing ATP (ATP is: adenosine triphosphate: a nucleotide derived from adenosine that occurs in muscle tissue; the major source of energy for cellular reactions - i.e. the molecule that carries energy to cells) . The final products of protein catabolism include carbon dioxide, water, ATP, urea, and ammonia.
More importantanly fats provide 9 cals per gram, compared with 4 for carbs and protein. Triacylglycerol,and other lipoproteins are not taken up directly by any tissue, but must be hydrolysed (decompose by reacting with water) outside the cell to fatty acids and glycerol, which can then enter the cell.
So clearly a diet high in fat, and low in carbs and high in protein is optimal for losing bodyfat, and more importantly visceral fat, but also to improve protein synthesis, energy and muscular hypertrophy/healing.
