The principle of reducing fat is that your body consumes more calories than it takes in, so your body consumes non-sugar substances such as fatty amino acids because you don't take in enough calories. Then why do you lose fat and gain muscle? As I said just now, the process of reducing fat will be accompanied by the consumption of some non-sugar substances such as amino acids. Amino acids are broken down by protein, and then the most important thing to gain muscle is protein, and protein will be broken down into muscle, so if you gain muscle first and then lose weight, it will lead to a certain degree of sharp decline in the muscles you added before, which is why.