The answer- and I bet this is predictable!- is: it depends. Protein is, indeed, the premier construction material for muscle. But the body needs a reason to use extra protein to build muscle- otherwise, the liver can convert protein calories into fat calories, and put them into storage as body fat.

The reason for the body to build extra muscle is, of course, exercise. When muscles are 'stressed' by physical exertion, the response is for them to grow and thus better accommodate the demand for work. The combination of muscle-stressing exercise (i.e., 'resistance' exercise) along with some extra protein is, indeed, a powerful formula for building muscle.

That said, most Americans- even those who exercise moderately- get ample protein to build and maintain muscle from their diets. The RDA for protein is 0.8 grams per kilogram of body weight per day. If you weigh 125 lbs, for example, that would translate to about 46 grams of protein a day- or a little less than 200 calories from protein. A mixed diet very readily provides this much. In fact, it readily provides twice this much.

The quality of protein matters too, however. To build muscle, you need all of the essential amino acids. These come from eggs, meat, and to a less extent dairy. To get them from other sources, foods must be combined- such as beans and grains, or nuts and grains. One potential advantage of a protein shake is that it is designed to provide all essential amino acids, and so could serve as a meal substitute. Generally, such shakes are made from whey protein (derived from dairy), or soy protein- or combinations.

Body builders can benefit from getting 2 to 3 times as much protein as recommended for the average person. But unless you are seriously engaged in the business of pumping iron and building muscle, you don't need all this extra protein- and there is some evidence it can be harmful to liver, kidneys, and bone over time.

To end this with a personal note, I work out about 90 mins a day- more when possible- combining aerobic and resistance training. I get all my protein from food, and make no effort to get 'extra.' No problem getting enough.

Hope this is helpful to you- and your muscles!

Best,
DK