A: This is a great question and especially at this time of year when we all have different health goals. There are some possible reasons why you have been losing muscle mass. Have you stopped training? Or have you changed your diet recently? Generally, when people start a new fad diet they are not taking in the calories that the body requires to build muscle mass. That’s generally why they result in quick weight loss. Try logging your calories and ask a professional how many calories you need every day. If you haven’t changed your workouts or your diet then I suggest you visit your doctor to find the cause.