If you are new to lifting, let's say less than 18 months, you can gain significant muscle mass while being in a calorie deficit. The training stimulus outweighs the body's reactions to being in a calorie deficit state. This is especially true if you are overweight to begin with. Many of my clients, and many studies show, and I have demonstrated, that this is very possible, if not common.
Once you have accumulated some training years, you probably will need to be in a slight calorie deficit to gain any appreciable mass. The key thing is to increase your calories judiciously. You don't want to accumulate fat as you go. Further, the amount of protein that you consume is key. Not only will high protein consumption reduce muscle loss while in a calorie deficit, it is the key to muscle protein synthesis as you go into surplus. 1.6 to 2 grams of protein per kilogram of body weight on a daily basis should be sufficient for most athletes.
Also of note is that the branched chain amino acid leucine seems to act as an on off switch for muscle protein synthesis. Recent research has shown that a minimum dosage of about 2.5 g of Leucine is needed to start the muscle building process, maybe slightly higher for adults over 40. You should get about this amount in a standard scoop of whey protein. Other protein sources will not be so high in this key amino acid.
Optimally, you should be getting your protein in at least 3 to 4 separate feedings per day.
Once you have accumulated some training years, you probably will need to be in a slight calorie deficit to gain any appreciable mass. The key thing is to increase your calories judiciously. You don't want to accumulate fat as you go. Further, the amount of protein that you consume is key. Not only will high protein consumption reduce muscle loss while in a calorie deficit, it is the key to muscle protein synthesis as you go into surplus. 1.6 to 2 grams of protein per kilogram of body weight on a daily basis should be sufficient for most athletes.
Also of note is that the branched chain amino acid leucine seems to act as an on off switch for muscle protein synthesis. Recent research has shown that a minimum dosage of about 2.5 g of Leucine is needed to start the muscle building process, maybe slightly higher for adults over 40. You should get about this amount in a standard scoop of whey protein. Other protein sources will not be so high in this key amino acid.
Optimally, you should be getting your protein in at least 3 to 4 separate feedings per day.