Most men reading this are under the assumption that more protein is better along with the idea that high protein diets are healthier, more satiating and pro-hypertrophy (muscle building). Now all of those are true to one degree or another, but most of the advise out there is really suited only for a) men on steroids and b) protein manufacturers who want to sell more tubs of powdered protein. At one time, I accepted the same dogma and was probably the typical guy out there that has consumed mountains of whey powders, egg whites, chicken and even a few raw eggs along the way. (Don't do that one please!) [As I became more plant-based, I downed boatloads of rice, yeast, hemp and pea protein.]
As time has gone on, I have grown to realize that there is almost NO science behind any of the protein requirements that I believed and below is a summary of some of the most important research:
1. Weight Lifters Need a Gram per Pound of Body Weight. False! This shocked me when I first read it, but there is NO evidence that you need a gram per pound of body weight. I simply cannot tell you how many times I have read this in bodybuilding magazines over the years and read it in forums and blog articles - too many to count. The truth is that the research shows that bodybuilders and strength athletes need between 0.5 - 0.8 grams per pound. And it should be mentioned that the 0.8 number is more for the serious strength athlete.
Where do I get that range of 0.5 - 0.8? Those are the current recommendation from the National Academy of Sports Medicine (NASM), who has merely summarized the research to date.  (NASM is one of the largest training organizations here in the U.S.) The ACSM has simiilar recommendations of 0.7-0.8 grams per pound for strength athletes.  These organizations did not just cherry pick a number out of the air, but rather did extensive research reviews. Again, study after study has shown the same thing: you simply do not get any benefits above about .8 gram per pound and the upper end is generally only for very serious athletes.
Stop and think about it: would college and professional athletic programs be interested in knowing how much protein their athletes need to consume in order to maximize muscle gains? Of course, and, as such, the subject has been extensively examined and the studies all say the same thing. Here is just one example and you can look at: The Effect of Protein Intake on Strength, Body Composition and Endocrine Changes in Strength/Power Athletes. This was probably the most recent of the studies and was particularly interesting, because it looked at athletes. Most of the other studies were done on beginners or untrained men and so the argument has been made that "hardened veterans" may need more. But, according to this study, that was not the case: athletes do not benefit from the gram per pound of protein either. [And the solid majority of you are Weekend Warriors like myself anyway.]
So let's take a guy like myself that lifts weights with some decent volume, but isn't prepping for a bodybuilding contest trying to bench 500 pounds, etc. I will actually likely do very well at HALF the protein mandated by the traditional advice. I weigh 165 pounds (75 kg), so rather than needing 165 grams of protein, I likely need about half of that or 83 grams.
Jeez - what a difference this makes! Trying to consume 165 grams of protein is painful,expensive and time consuming. And I did for years, so I know what I'm talking about. Trust me - a big part of your day will be remembering, preparing and buying protein in foods and powders. Every couple of hours you'll be forcing down more of the stuff and there will a nagging thought in the back of your head asking, "Is this really natural? Why am I doing this again?!?" The truth is that it's not very natural and consuming feeding bags full of protein powders probably isn't as well for many reasons.
But let's go back to my actual requirement of 83 grams. This is much more doable. In fact, I can get this almost from food alone. I'm a mostly plant-based guy, but I can easily get 45-60 grams of protein just from what I put on my plate. If I throw in a couple of scoops of protein powder, I'm up to 83 grams easily. This requires little to no extra time out of day and little extra expense as well. If I want to play it safe, I can throw in another scoop or some (BPA-free) sardines, etc.
So where did the 1 gram per pound of bodyweight theory come from? I believe it came from the steroid community. Men on steroids will push their testosterone to 2500+ ng/dl and they have a much greater capacity for muscle growth than those of us staying physiological. In their case, they can probably make use of the extra protein consumed. I have read many articles about and quotes by these top steroid bodybuilders and they absolutely believe that consuming at least 1 gram per pound is essential and some talk about 2+ grams. However, the steroid lifestyle is generally not a sustainable one for many reasons and so, to be frank, I regret ever reading those kind of articles. I should have stuck to the scientific journals!
2. Endurance Athletes Need a Gram per Pound of Body Weight. Again, this is another total myth: the recommended protein levels for endurance athletes are 0.5-0.6 grams / lb for both NASM and ACSM.  No benefit has been found by exceeding these protein levels.
3. Protein Increases Testosterone. Actually, the opposite is true according to a number of studies. This is something that I will cover in more detail on another page, but a few studies show that both total protein and a higher protein/carbohydrate ratio likely lead to decreased testosterone levels. 
4. Protein Is Good For You and Increases Longevity. Of course, some protein is good for you - no one disputes that. But the real truth is that overly high levels of protein likely accelerate aging and may increase your risk of cancer. Can I prove that? Well, give me a chance here as I have to give you a little background:
First of all, the protein in food is always composed of a blend of amino acids. If you buy any protein powder, just look at the label on the jug and you can see all the constituent aminos contained and in what amounts. One of these aminos will be methionine and it ramps up IGF-1, which stands for Insulin-Like Growth Factor. IGF-1 is aptly named, becasue growth is what IGF-1 is all about. It's extremely important when you are young as deficiencies can result in a small stature and height. IGF-1 is also considered anabolic: "the hypertrophic effects of muscle-specific IGF-I infusion are well documented in animal models and muscle cell culture systems."  Clearly, IGF-1 seems like a good thing and something us guys want an abundance of, right?
The answer is 'yes' if you are less than 20 years old. After that, you probably want to begin ramping down IGF-1 levels (but not too much of course). The reason is that IGF-1 is extremely powerful and essentially signals many different tissues - not just muscle - to "grow! grow! multiply!" (Insulin does the same thing.) This is why higher levels of IGF-1 have been associated with many kinds of cancer. Basically, high levels of IGF-1 are analagous to the body having its foot on the accelerator 24/7 and that, of course, is not going to extend longevity.
But the story doesn't end there unfortunately. IGF-1 will also ramp up oxidation (free radicals) in the mitochondria. Now you don't want to go too low with IGF-1 - that is associated with Alzheimers and other neurological disorders - but you also don't want to go too high. If you go too high, you are overheating your engine effectively. Most men consuming a lot of protein from what I have seen on Peak Testosterone Forum will end up with IGF-1 on the high side of the lab range. My last test showed this and it means that I am likely increasing mitochondrial-related damage - and they are the furnaces of your cells - in many tissues of my body.
There are many,. many example of this from the literature, but let's look at just one. One of the landmark anti-aging strategies is called caloric restriction. Caloric restriction basically means reducing your calories until your body begins conserving and slowing down such that aging is also decreased and longevity is extended. The effectiveness of caloric restriction has been verified in many animals and, recently, in primates as well (although more research is needed to make a long story short). One of the ways that caloric restriction works is by increasing a protein complex called SIRT1. IGF-1 actually limits the increase in SIRT1 from caloric restriction:
"Another study provided evidence that insulin and IGF-1 attenuated SIRT1 activation induced by caloric restriction." 
Bascially, IGF-1 (and increased insulin levels) partially undo the benefits of caloric restriction! If you're 55 like me, you probably do care about such things and you would like to decrease your risk of cancer and slow down the acceleraton into the grave.
CAUTION: IGF-1 levels vary according to a number of factors in the diet - not just protein levels. It is better to pull the number before and after you make any dietary changes and monitor it for yourself. Studies deal with averages and you may not be "average." You can pull your IGF-1 inexpesnively without a direct doctor's orders here: Testosterone Labs.
1) Br J Pharmacol, 2008 Jun; 154(3):557 568, "Regulation of muscle mass by growth hormone and IGF-I"
2) Biochemical Society Transactions, 02/2013, 41(1):101-5. "Metabolic triad in brain aging: Mitochondria, insulin/IGF-1 signalling and JNK signalling"
3) NASM Essentials of Sports Fitness, Chapter 17 (Nutrition), p. 474-475.
5) J Appl Physiol. 1997;82:49 54, "Testosterone and cortisol in relationship to dietary nutrients and resistance exercise"
6) Life Sci, 1987;40:1761 1768, "Diet-hormone interactions: protein/carbohydrate ratio alters the reciprocally the plasma levels of testosterone and cortisol and their respective binding globulins in man. Life Sci. 1987;40:1761 1768.