Determining Sufficient Protein Intake

[blue9steel]

The main goal of bodybuilding is to improve one's physique and the two main ways to do that are to reduce bodyfat and increase muscularity. Muscle tissue is built out of proteins, which are turn assembled from amino acids, so getting the right mix and getting enough intake at the right times can go a long ways towards helping you to reach your goals.
When you look up the nutrition data for a food, Top Sirloin for example, you're going to find the total protein listed as grams. For cooked choice grade that's about 7.5g of protein per ounce. Protein is built out of individual amino acids so you'll also find a list looking something like this:

Tryptophan 51.5mg
Threonine 313mg
Isoleucine 357mg
Leucine 624mg
Lysine 663mg
Methionine 204mg
Cystine 101mg
Phenylalanine 310mg
Tyrosine 250mg
Valine 389mg
Arginine 507mg
Histidine 250mg
Alanine 477mg
Aspartic acid 714mg
Glutamic acid 1177mg
Glycine 477mg
Proline 374mg
Serine 309mg
Hydroxyproline 82.3mg

There are roughly 22 standard Amino Acids known to be involved in the human diet. Many of them your body can make itself if necessary. There are nine essential amino acids that you can only get through food: phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine. Six are "conditionally essential" meaning there are times when you can't make enough of them, they are: arginine, cysteine, glycine, glutamine, proline and tyrosine.
Ok, so why do we care about any of this? Not taking in enough of the right type of "building blocks" means your body will run out of parts while it's trying to maintain or construct muscle and obviously that's contrary to our goal of looking fit. Protein sources come in two types, complete, which means they have a full complement of amino acids in a good ratio, and incomplete which means they're missing some or have sub-optimal ratios. Complete proteins include meat, eggs and dairy. Plants sources that are close enough to complete include: Quinoa, Buckwheat, Seaweed, Amaranth, Hempseed, Chia, Potatoes, Soy (may cause hormone problems). For incomplete proteins you can practice food combining which pairs foods with different deficiencies to make a whole protein meal. Here's a handy chart showing how to do that:

Grains ----- Seeds
|| \\ / ||
|| X ||
|| / \\ ||
Dairy ----- Legumes

Double lines are good combinations, single lines are only mediocre.

The good news is as long as the majority of your protein comes from animal sources you can ignore most of the amino acid complexity issue as you'll tend to get plenty of the right types in roughly the correct amounts. Vegetarians, well you're going to have to work harder but it's still doable.
So the next question is, how much protein do we actually need? There are two main things protein does for you, the first is to provide sufficient building blocks so you can build and maintain muscle tissue, the second, and this is recently discovered, is to activate mTOR (mammalian target of rapamycin) via your intake of Leucine. mTOR works as a biological switch which essentially turns on expensive bodily processes like muscle protein synthesis.
Let's focus on the raw materials portion for a minute and see if we can nail down how much protein we actually need to eat daily. There are a variety of different recommendations out there and they vary depending on who is giving them, their objectives and assumptions:
1) Anecdotal bodybuilding recommendation 2.2g/kg of bodyweight
2) RDA amount to prevent muscle wastage 0.8g/kg of bodyweight
3) International Society of Sports nutrition 1.6-2g/kg of bodyweight
4) Some experts recommend 50%-100% more than the bodybuilding amount
So these recommendations are all over the place, why is that? Well, the RDA just establishes the minimum intake you need to stay healthy, they're not really concerned with building lots of muscle mass. The experts with the really high recommendations are generally dealing with populations that make heavy use of steroids, and they tend to significantly increase your requirements. Perhaps we could check in with the scientists and see what they have to say:

Consolazio 1975 Positive NBAL at 1.39g/kg, 2.76g/kg > 1.39g/kg
Walberg 1988 1.6 > 0.8 NBAL somewhere between the two
National Academy of Sciences National Research Council 1989 NBAL at 1.35g/kg, 1.69g/kg 2stdev (multiple study meta-analysis)
Fern 1991 NBAL at 1.3g/kg
Tarnopolsky 1992 NBAL 1.41g/kg, recommended 1.76g/kg 1stdev, 2.11g/kg 2stdev
Lemon 1992 NBAL 1.53g/kg, recommended 1.73g/kg 2stdev
Campbell 1995 NBAL between 0.8-1.62g/kg
Layman 2004 1.6g/kg > 0.8g/kg
Mettler 2010 2.3g/kg > 1g/kg
Phillips 2011 1.3-1.8g/kg max protein synthesis, 1.8-2.0g/kg prevent lbm loss in deficit
Pasiakos 2013 Optimum intake between 1.6-2.4g/kg
Helms 2013 2.3-3.1g/kg of Fat Free Mass
Antonio 2014 4.4g/kg !> 1.8g/kg

There are plenty of other studies but these tend to tell the story. Bottom line pretty much everyone agreed that the RDA was too low for people engaged in strength training. There was very little evidence that intakes greater than 1.8g/kg were beneficial and the optimum intake seems to be at about that level if we want to be absolutely sure we're getting everything we need.
Wait a minute though, why is the bodybuilding recommendation usually 2.2g/kg, is it just because that is 1g/lb and that's an even and easy to remember number? Or maybe it's because they're just being extreme and taking more than they really need? As it turns out, it's likely a different reason altogether. Recent research suggests that muscle protein synthesis is turned on by mTOR which is activated either weakly by Insulin/IGF-1 through the PI3K/Akt pathway or much more strongly by Leucine through it's own pathway. That means whenever you eat protein you're helping to flip on the switch for the conveyor belts at the muscle factory as well as supplying raw materials for construction.
So far, the scientists haven't pinned down exactly how much Leucine you need to take in to maximize signalling, I've seen a variety of studies with amounts ranging from 0.0264g/kg - 0.05g/kg per meal. In many cases though, when eating real food this is going to mean taking in a higher amount of protein than the earlier 1.8g/kg number we talked about. The science does say that the signalling effect is refractory (a fancy word that means if you take your meals too close together the signalling effect is less) and that eating meals about 4-6 hours apart seems to be roughly optimum. Given that we all need to sleep, that means your best meal frequency is going to be between 3-5 with 4 probably being best.
The above effect is combined with the fact that a number of studies have shown protein intake requirements rise when in a calorie deficit:

Munro 1964 2g N (1g N = 6.25g Protein) for each 1000 calories surplus/deficit
Chiang 1988 1.94g N for each 1000 calories surplus/deficit
Lemon 1995 Inverse relationship between energy intake and protein requirements

Putting all that together, it means that the bodybuilders weren't so far off after all and in some cases even the 1g/lb recommendation could be a bit light. Ok, so let's wrap this up. I don't know about you, but I want to be sure I'm getting all the possible benefit I can, but there is no point in going overboard if it's not going to help. Here are the highest numbers that seem to be supported by research:

Normal daily intake 1.8g/kg
Daily intake while cutting 2.0g/kg
Per meal intake 0.05g/kg of Leucine
Most meats average 8% Leucine so that's 0.625g/kg of protein per meal times four meals gives up to 2.5g/kg daily
Of course whey is about 11% Leucine which translates to 0.455g/kg

Bottom line, 1.134g/lb (evenly spread over four meals) is pretty much the limit of what we can expect to be helpful, and in many cases 1g/lb or slightly less (0.82g/lb) is plenty.