You are on a weight loss diet and losing weight. You are not doing any kind of exercise. But you lose weight. You are not getting any more protein despite being low in calories. But you are losing weight. Good, isn’t it?
Well, no. If you’re on a crash diet, aren’t getting enough protein, and aren’t exercising, you are most likely losing more lean mass than body fat. And this will lower your metabolism.
Let’s be clear: the diet to lose only fat mass does not exist. There is no magic button that pushes the body to burn fat and not to sacrifice muscle, so in all weight loss there is always a loss of lean mass.
The point is: try to reduce the loss of lean mass and promote the loss of fat mass.
But how do you know that you are losing more lean mass than flab?
First of all, here are 5 signs.

ARE YOU LOSING MORE LEAN OR FAT MASS?
5 SIGNS TO FIND OUT
1) You lose weight too quickly: losses greater than half a kilo despite a deficit of 3500 calories per week are due to the loss of water and the use of lean mass to produce energy. But even in the case of large caloric deficits, the body resorts to the destruction of lean mass to get what it does not get from food. So if you are losing weight fast you are not losing any flab.
2) You have low energy levels and feel less strong: it means that your metabolism is lowering more easily than expected, and this is because you are losing lean mass. 3) You have reached the stalemate:

initially you lost weight as fast as a train, then suddenly as well as feeling tired, the weight decreases more. End of the magic? No, metabolic stall. And the more you are on a diet, the easier you can stall in a short time.
4) You have mood swings and you feel stressed, you sleep little: the muscular and nervous systems are connected.  When you lose lean mass, you are more prone to periods of exhaustion.
5) If you play sports, you are incredibly hungry and do not recover well: suddenly the weights are very heavy, the activity weighs you down, even just walking tires you. Also, you have uncontrollable hunger. More fatigue is reflected in more stress again. And the body holds onto its fat reserve tightly.
(Source: Dr Albert Matheny for Women’s Healt Magazine)