Are these claims true? If so, do we know how much protein is actually safe?
And what if we can eat an unlimited amount of protein and all these claims are simply hyperbole. If this is the case, is there a balanced diet that is perfect for the average adult? For the average fitness fanatic? For the average hardcore bodybuilding freak?
Related: Bolster Your Daily Protein Intake Using Top Quality MTS Whey
In this article I am going to address the following statements, and provide the truth regarding each, as we know it today.
- Protein intake places a strain on the kidneys
- Meat (protein) will give you cancer
- Extra protein intake can't be properly digested
Too Much Protein - Is There Such a Thing?
Protein Intake Places a Strain on the KidneysThe argument is that too much protein brings in an unwanted amount of nitrogen into the human body. This nitrogen must be processed by the kidneys, and ultimately expelled in the urine. It is often said that this demand can cause kidney issues, kidney disease, and even kidney cancer.
Obviously, those with pre-existing kidney conditions should consult with their physicians before embarking on a high protein diet. But what about those of us with normal, healthy kidneys? Does eating 200 or even 300 grams of protein per day pose a serious health concern?
Research does not support the notion that eating a larger than normal amount of protein causes harm to healthy kidneys.  Chris Kesser, New York Times best-selling author and a top natural health expert, had this to say,
"However, just because a low-protein diet can be therapeutic for those with kidney disease, doesn't mean a high-protein diet causes kidney disease in the first place. What I'm addressing here is the notion that high-protein diets cause kidney disease in healthy peoplewhich is not, as you'll find out, supported by research.
Since one of the main biological roles of the kidney is to metabolize and excrete nitrogen byproducts from protein digestion, many people believe that eating more protein will strain' the kidneys. There is an upper limit to the body's ability to metabolize protein, but the brain has specific mechanisms that regulate desire for protein, and these mechanisms are difficult to override through willpower alone.
It's clear from controlled trials that high-protein diets do induce measurable changes in kidney function. The sticking point seems to be in how these changes are interpreted, because while some researchers view hyperfiltration as a sign of kidney stress and even damage, others view it as the kidneys simply getting better at doing their job."Hyperfiltration is a normal and adaptive response. It allows the kidneys to better process extra protein intake. Hyperfiltration does not appear to be a pathological condition that eventually leads to kidney disease, as it is often painted to be. 
Meat (Protein) Will Give You CancerThis is a shocking statement. The proclamation that meat causes cancer obviously brings with it the fear of consuming too much protein. The knee jerk reaction is to over-consume carbs.
Fat intake is still considered evil by the general public, though this notion is completely misguided. Add to it the fear of eating protein foods, and we now have a general population that is completely carbohydrate reliant. While an excessive amount of carbs might not be the best choice for long-term health, and this point is obviously debatable, a carb-heavy diet is unbalanced and probably not the best choice for overall health.
But let's not head down a rabbit hole. Does meat consumption cause cancer?
A study from 2014 reported an association between high protein intake and the incidences of cancer.  This observational data was collected on individuals ages 50 to 65.
One of the interesting findings in this study (that isn't reported) is the mortality rates of meat-eating folks over the age of 65. They actually had lower incidences of cancer. It should be noted that a high protein diet was defined as one in which at least 20% of calories came from protein.
Another point of note. The discovered relationship between cancer and protein consumption only existed for animal-based proteins. Plant protein did not seem to increase cancer rates.
It is hypothesized that higher protein intake increases IGF-1 activity. The thought is that might lead to higher cancer rates and an earlier death. We must repeat that this is merely speculation.
Another study on mice backed this hypothesis. Researchers found that a diet consisting of 18% protein intake or greater resulted in larger tumor size. This was compared to a very low protein diet of only four to seven percent.
It must be stated that the original study we looked at was epidemiological in nature. It was not a clinical trial. Epidemiological information cannot (read that word a second time please) be used to say that A causes B. Epidemiological studies only exist to prompt deeper research.
We have no clinical proof that animal protein increases cancer rates.
So let's cut to the bottom line, and that is diet quality. IGF-1 causes cell growth. It doesn't care if this is a healthy cell or a tumorous cell. If you are taking care of yourself and eating properly, your risk of cancer is much lower. This is an obvious conclusion. If you are not taking care of yourself, and have a great likelihood of actually having cancerous cells in your body, spiked IGF-1 may not be the best thing for you.
The conclusion? If you are in a low-risk cancer group, then a high protein diet isn't much of a concern. If you are eating poorly already and not taking care of yourself, or you already have cancer or a high genetic predisposition for cancer, then it might be wise to monitor your overall protein intake.
Eat right. Exercise. Don't smoke. Take care of your body.
Examine.com concluded that a more appropriate title for this study would have been, 
"A more accurate headline for this study would have been 'High protein for those between 50 years to 65 years old who have poor diet and lifestyle habits may be associated with increased cancer risk.' "
Extra Protein Intake Can't Be Properly DigestedIn a recent New York Times article called, "Can You get Too Much Protein?", registered dietitian Jim White stated:
"The body only digests and absorbs a certain amount of protein at every meal (about 20 to 40 grams). You're robbing yourself of other macronutrients that the body needs, like whole grains, fats, and fruits and vegetables."What happens to any extra protein that is eaten? The implication is that it is wasted, perhaps broken down into sugar and stored as fat.
Let's dig a little deeper into what's being said here.
First, it must be stated that eating a quality amount of protein each day does NOT rob your body of other valuable macronutrients, or even micronutrients for that matter - if - you are eating a balanced, reasonable diet filled with a substantial amount of clean, whole foods. If you're not eating clean foods to begin with, then does it really matter how much protein you eat? Your diet is filled with junk to begin with.
So, assuming you're eating a diet centered around healthy choices, let's break down a typical "high protein" diet.
Most males in the fitness community consume about 140 to 220 grams of protein per day. This is a safe assumption for about 90% of male gym rats, and would be considered a high protein diet when compared to a more typical diet.
It's also a safe assumption that the average male is probably eating somewhere between 2500 to 3500 calories per day, depending on age and goals (weight loss, maintenance, or weight gain). So let's split the difference and assume the average 20-something male that eats healthy and works out three to five times per week is consuming 3,000 calories.
At 3,000 calories, even 220 grams of protein per day only shakes out to 880 calories. That's a mere 29.33% of overall daily caloric intake. Less than 30%. This leaves room for about 70% of calories to be filled with veggies, fruits, grains, healthy fats, and all the other foods that the New York Times expert dietitian stated would me lacking in a high protein diet.
Clearly, his opinion is nonsense. Veggies are not calorie dense at all. You'll be able to eat a boat load of veggies to fill in these 2,100 plus remaining daily calories. That's a lot of fiber and healthy micronutrients.
But what about women? A "high protein" diet for the average fit and healthy woman might be 90 to 140 grams per day. For sake of example let's go with 110 grams. Most women, even those that are religious about working out, struggle to consume much more daily protein than that.
110 grams of daily protein equates to 440 calories. Assuming a 1700 to 1800 daily calorie intake, which might even be on the low end, this equates to only about 25% of daily calories. Again, this leaves about 75% of daily food choices open to fruits, veggies, fiber, and healthy fats.
Moving on to the claim that the body can only handle 20 to 40 grams of protein per meal. Research on intermittent fasting tends to hint that this isn't true.
Two separate studies came to the same conclusion - that the mass consumption of protein in a short period of time result in no difference in body lean muscle mass.  The bottom line: It appears that the body can handle far more protein than we expected.
The question is why?
The human body is very effective at adaptation, especially when it comes to resources at hand and efficiently utilizing them so they are not wasted. This appears to be true with protein intake and amino acids.
The human stomach uses an acid bath to turn food into what's known as chyme. Chyme is then moved through the intestines where it gets "eaten." This is the process of nutrient absorption. Chyme is not absorbed based on what time it was created. This means that the intestines don't distinguish between morning chyme (and protein) and a late morning snack that is turned into chyme.
Chyme is chyme.
Chyme also doesn't stay in the intestines for the same amount of time. Its digestion varies.
Amino acid transporters digest the protein, or amino acids, found in chyme. Around 91 to 95% of amino acids are absorbed by these transporters. Hourly rate of digestion can fluctuate between 5 to 10 grams.
Digestion of protein and amino acids is very much self-regulated. The digestive hormone CCK has the ability to slow down intestinal contractions and transport speed in response to the amount of protein that is currently being digested.
Simply stated, the body has the ability to slow down the rate at which it processes protein so that it absorbs the bulk of the raw fuel it's been given.
This physiological reality destroys the belief that only 20 to 40 grams of protein per meal can be utilized.
ConclusionHere are the facts.
First, a high protein diet does NOT destroy healthy kidneys. In fact, the noted reaction to addition protein intake is likely a healthy and normal function of the kidneys, allowing it to properly process the demand being placed upon it.
Second, a high protein diet MIGHT be a bad choice if you have a high genetic predisposition to cancer, or if you currently have cancer, or if you eat a brutally bad diet and don't take care of yourself. Even with this established, there is no clinical research to back this hypothesis.
Third, a high protein diet (as the NY Times expert claims) does not take away from your ability to eat fruits, veggies, fiber, and other healthy fats. This is utter nonsense.
Finally, the body can handle more than 20 to 40 grams of protein per meal. This is a physiological reality. Here again the NY Times fails to present quality, factual information.