In order to induce muscle hypertrophy (growth) an increased amount of amino acids needs to be consumed to increase and maintain protein synthesis and positive nitrogen balance. This is plain to understand and most people know this. But the real question boils down to exactly how much protein does a person really need to get to that level? Although there are various factors involved, including whether or not the person is weight training and looking to add new muscle tissue, that individuals weight, and the type of protein being consumed, you are likely to get a straightforward answer in the amount of a certain number of grams -- depending on who you ask.
Supplement manufacturers often tout the claim that you need 1-2g of protein per pound of bodyweight daily in order to grow. But is this really a realistic number and how did they come to this conclusion? The truth is this is actually a serious exaggeration when looking at the scientific evidence, although it is somewhat lacking when looking at heavy weight training males who workout using a serious bodybuilding/mass building routine. Nonetheless, these results can still be interpolated for the average person and we can probably all afford to bring our protein consumption down to a more realistic level.
A recent LA Times piece quoted bodybuilding.com moderator and all around nutrition guru Alan Aragon with some good realistic numbers on the quantities of protein a person should be consuming for steady growth.
Aragon deals with more ambitious populations. For new weightlifters aiming to both lose fat and build muscle, he recommends 1.7 grams of protein per kilogram of body weight per day. Those focused merely on adding muscle need only 1.4 grams, he says. A 180lb person would equate to 82kg so that would average out to 139g of protein per day for that person looking to build muscle. Of course, most of the protein in a persons diet should be coming from whole food sources, and not protein supplements. As Alan points out, protein shakes are more a matter of convenience. It can be hard to consume that amount of protein per day from whole food sources, so powdered whey, milk, eggs or soy make it much easier to supplement additional protein into the diet. This is especially true when a typically bodybuilder/weightlifter diet is composed around eating meals every 2-3 hours.
In a paper published by The Journal of the International Society of Sports Nutrition (JISSN), they go even further on the topic.
Protein Requirements for Resistance Trained AthletesIn a recent Meta Analysis on protein requirements Rand et al. defined the protein requirement in healthy adults as "the continuing intake of dietary protein that is sufficient to achieve body nitrogen equilibrium (zero balance) in an initially healthy person of acceptable body composition at energy balance and under conditions of moderate physical activity..." An individual's protein needs are assumed to have been met when the amount of nitrogen consumed is equal to the amount of nitrogen excreted or lost (zero nitrogen balance). In the occurrence that the amount of nitrogen consumed exceeds the amount of nitrogen lost then the individual is in a state of positive nitrogen balance, and is generally assumed to be in an anabolic state. Conversely when the amount of nitrogen excreted exceeds the amount of nitrogen consumed, the individual has entered into negative nitrogen balance, and is assumed to be in a state of net bodily protein loss (catabolic state). Based on this definition, the Recommended Daily Allowance (RDA), meant to suffice for 97.5% of the population is 0.8 grams of protein per kilogram of bodyweight. However, strength training athletes generally consume a great deal more than the RDA, with the rationale that their protein requirements exceed that of the general population. Therefore, a number of studies have examined athletes' protein requirements based on the nitrogen balance technique. [Italics added] 
The paper goes on to review a number of studies looking at protein intake in a variety of individuals, but noting specifically that those who are doing extensive bodybuilding and/or weight training will still more than likely need to exceed protein intakes of the average individual because of their need to increase muscle hypertrophy beyond standard levels. They also compare rates of digestion of different types of protein (fast vs. slow) and optimal protein timing, which can all get very confusing and bog down the average weight trainer who wants to skip the theoretical and get down to the nuts and bolts. For those people, I encourage them to read Will Brink's article, The Religion of Pre and Post Workout Nutrition.
JISSN also includes a practical applications table of protein and amino acid consumption and supplementation at the conclusion of their article which can help shed some light on their conclusions. I have reproduced the table below. Interestingly, they recommend the consumption of essential amino acids (EAAs) in the place of a full source protein in many cases.
|Pattern of Digestion||Alternate normal meals with fast digesting sources of protein or EAAs.|
|Rate of Digestion||Protein balance is greater with slow proteins with no |
additional energy; however, when combined with a source of energy, whey protein produces A greater protein balance than casein combined with a source of energy.
|Timing of Protein Ingestion||Consume EAAs or fast digesting protein prior to and immediately following exercise.|
|Protein Quality||An omnivorous diet appears to be optimal for fat free mass and indexes of performance, while supplementing with EAAs may enhance protein accretion along with normal protein feedings.|
|Amount per serving||Unsure, but Dangin et al. found an increase in protein synthesis from 23 to 33 grams of whey protein. This may be near the limit as 40 grams of EAAs did not increase MPS in comparison to 20 grams of EAAs.|
|Energy Source combined with Protein||Both carbohydrates and fats appear to spare protein equally. However, carbohydrates |
are still critical for maintaining intensity during resistance training.
The amount of protein that can be adequately consumed and digested in one sitting appears to be around the 30g mark and Will Brink makes the argument that it really doesn't matter, because as he says "You've gotta eat something."
The Counter Argument
In his anti-supplement book, Muscle, Speed, & Lies, author David Lightsey makes the case that none of these figures our accurate and the actual amount of protein necessary to be consumed daily -- even by weight training individuals is very low. The text below is quoted from Chapter 5 "Protein and Muscle Mass: How much is Enough?"
Everybody knows muscle is mostly protein. Everybody also knows that a lot of extra protein is required to build muscle and keep it healthy. Right? Well, actually, it's not. Everybody is wrong. Similarly, most people believe that muscle is anywhere from 75 percent to 100 percent protein. In fact, muscle is roughly 70 percent water! It contains only about 22 percent protein. Stop here a moment, and do the math. Let's say you want to add a pound of muscle to your current body weight per week. If a pound of muscle contains 22 percent protein, how many grams of protein must you consume beyond your normal diet to achieve this goal? 22 percent of one pound (454 grams) = roughly 100 grams. If one pound of muscle contains roughly 100 grams of protein, how many extra grams of protein will you need to consume per day? 100 grams/7 days = 14.3 grams per day. [Italics added] Although this sounds like a grossly confused calculation for those of us raised to believe you need 1g of protein per pound of bodyweight, Lightsey backs up his argument with advice from doctors and sports nutritionists. His view of the supplement industry is extremely low, but he does make good points that I agree with -- namely that two of the most ergogenic substances you can consume are water and carbohydrates.
On the flip side of the coin, Will Brink, in his article Protein Myths that Will Not Die, counters this argument with one of his own.
Myth #4 “Athletes don’t need extra protein”
Interestingly, there has not been much new research of note on this topic since I wrote the first version of this article in 1995. Now the average reader person is probably thinking “who in the world still believes that ridiculous statement?” The answer is a great deal of people, even well educated medical professionals and scientists who should know better, still believe this to be true.
[...]For the past half century or so scientists using crude methods and poor study design with sedentary people have held firm to the belief that bodybuilders, strength athletes of various types, runners, and other highly active people did not require any more protein than Mr. Potato Head…..err, I mean the average couch potato.For those of you who may need a brush up, one review paper on the subject by one of the top researchers in the field (Dr. Peter Lemon) states “…These data suggest that the RDA for those engaged in regular endurance exercise should be about 1.2-1.4 grams of protein/kilogram of body mass (150%-175% of the current RDA) and 1.7 – 1.8 grams of protein/kilogram of body mass per day (212%-225% of the current RDA) for strength exercisers” (“Is increased dietary protein necessary or beneficial for individuals with a physically active life style?” Nutr. Rev. 54:S169-175, 1996).Another group of researchers in the field of protein metabolism have came to similar conclusions repeatedly (“Evaluation of protein requirements for trained strength athletes.” J. Applied. Phys. 73(5): 1986-1995, 1992.) They found that strength training athletes eating approximately the RDA/RNI for protein showed a decreased whole body protein synthesis (losing muscle jack!) on a protein intake of 0.86 grams per kilogram of bodyweight.
From all the research that's out there it appears that the best source of protein for any diet is from whole food sources. The body is simply more apt at digesting protein from nature when combined with fats, carbs, enzymes, vitamins and minerals and the whole range of other ingredients found in a balanced and nutritious meal. However, for a bodybuilder or weightlifter who is trying to add significant amounts of muscle mass in a short period of time, an increased amount of protein is necessary. Obviously in a perfect setting that person would get all their protein from whole food sources. But, in a fast paced world with our lives to lead, most of us will opt for the convenient option of supplementing with a protein shake or bar in place of a meal. The most important times to consume these quick digesting proteins is around the workout period, where amino acids are needed quickly to be utilized by muscle tissue. It appears from the research that the optimal amount of protein from a supplement that can be consumed in a single setting is around 30 grams. According to JISSN, a fast digesting whey protein or even an EAA supplement appears to be your best choice for this purpose (although whey is a much cheaper alternative to the free form essential amino acids).
 Fell, James. Rethinking protein powder. Los Angeles Times. September 27, 2010.
 Wilson, Jacob, et al. Contemporary Issues in Protein Requirements and Consumption for Resistance Trained Athletes. J Int Soc Sports Nutr. 2006; 3(1): 7–27. PMCID: PMC2129150
 Lightsey, David. Muscles, Speed, and Lies: What the Sport Supplement Industry Does Not Want Athletes or Consumers to Know. The Lyons Press. 2006.