High-Protein Diets - Bad for Health & Kidney Function?
Protein supplies the building blocks of life. Every cell uses protein (and the amino acids comprising it) to build, maintain, and reinforce its structure as well as support various cellular functions it performs. Protein is also needed to build and repair muscle tissue, bolster immune function, and support neurotransmitter synthesis.
Yet, despite the importance of protein, there has been a number of myths permeating throughout the fitness industry regarding this essential macronutrient. Some say it will damage your kidneys while others believe it’s detrimental to long-term bone health. This back and forth battle over the safety and efficacy of protein has raged on since the 1980s.
Related - How Much Protein Do You Need?
Today, we’re going to take a look at the most recent scientific research to see whether these beliefs about protein are fact or fiction and answer the question on many fitness newbs’ minds:
Is a high-protein diet dangerous?
Let’s get started!
What is Considered a “High-Protein” Diet, Anyway?
While a wide range of protein intakes have been classified as “high protein” over the previous decades, most of those studies based protein intake off of percentages of total calorie intake, such as 20%, 30%, or 35%.
A more accurate description of “high-protein diets” has been posited by members of the International Society of Sports Nutrition (ISSN) which is based on a person’s body weight.
Antonio et al (2016) put forth the notion that a diet qualifies as “high protein” if an individual’s protein intake exceeds exceed 2.0 g/kg/day.  For those of you not using the metric system, 2.0g/kg is roughly equal to 0.909g/lb of bodyweight.
Researchers based this number off of the 2007 position stand by the ISSN which stated that “protein intakes of 1.4–2.0 g/kg/day for physically active individuals is not only safe but may improve the training adaptations to exercise training”. 
Now, it should be noted that the ISSN updated its position stand in 2017, in which they note: 
“For building muscle mass and for maintaining muscle mass through a positive muscle protein balance, an overall daily protein intake in the range of 1.4-2.0 g protein/kg body weight/day (g/kg/d) is sufficient for most exercising individuals, a value that falls in line within the Acceptable Macronutrient Distribution Range published by the Institute of Medicine for protein. Higher protein intakes (2.3-3.1 g/kg/d) may be needed to maximize the retention of lean body mass in resistance-trained subjects during hypocaloric periods. There is novel evidence that suggests higher protein intakes (>3.0 g/kg/d) may have positive effects on body composition in resistance-trained individuals.”
More on that last part up next!
High-Protein Diets and Kidney Function
Debate over the safety of high-protein intakes has seemingly occurred over the past 30+ years, yet researchers have known for over 90 years that high-protein diets are detrimental... When kidney function is compromised that is.
Jackson et al. observed that diets high in protein resulted in moderate to severe renal damage in rats when they had one kidney removed.  Of course if social media was around in 1928, headlines would have read:
“High protein diets are bad” instead of “high-protein diets harmful to rats missing one kidney.”
Regardless, the groundwork was laid for the idea that high-protein diets were detrimental to one’s kidneys, and the notion has continued to permeate in fitness circles ever since.
Fortunately, a number of studies, reviews, and meta-analyses have been carried out in recent years to assess the validity of the notion regarding high-protein diets begin harmful to a person’s kidneys.
And every single one of these studies shows that in otherwise healthy individuals, high-protein diets do NOT impair kidney function, adversely affect glomerular filtration rate (GFR), or electrolyte balance. [3,8,9,10,11,12,13,14]
Note: GFR is a test to measure how efficiently the kidneys filter blood and remove waste.*
In fact, one study had healthy, resistance-trained men consume a high protein diet, consisting of ~2.51–3.32 g/kg protein per day for an entire year and found no harmful effects on measures of blood lipids or liver and kidney function.  In addition, despite the total increase in energy intake during the high protein phase, subjects did not experience an increase in fat mass.
Another study gave resistance-trained men a daily protein intake of 4.4g/kg (2g/lb) for eight weeks and observed no detrimental effects to kidney function.  FYI, 4.4g/kg of bodyweight is roughly FIVE times the RDA for protein intake.
To get this much protein from chicken, steak, etc would be rather difficult for most people, so subjects in the groups also consumed whey and casein protein shakes to help hit the 4.4g/kg/day protein intake.
Additionally, not only were the men consuming an exceptionally high protein diet they were also consuming a hypercaloric diet to the tune of ~800-kilocalorie surplus. Yet, despite this considerably large surplus, they did not gain significant amounts of body fat, even though their training volume remained consistent with their pre-trial training regimen. This interesting phenomenon has led researchers to consider the fact that the macronutrient an individual consumes in excess may impact how their body handles that excess energy (increasing lean mass, fat mass, etc.)
Most recently, a 2019 systematic review investigating links between protein intake, kidney function, and mortality found that baseline protein intake was not associated with decline in kidney function and that long-term low protein intakes (<0.8 g/kg/day) may increase risk of mortality. 
Suffice it to say that if you are an otherwise healthy individual, who trains regularly and has two functioning kidneys, high protein diets do not pose any inherent dangers or damage your kidneys.
Now, if you are someone with impaired kidney function or have chronic kidney disease (CKD), it’s another story entirely, and protein intake should be monitored, as research demonstrates that a high-protein diet may worsen kidney function due to the difficulty CKD patients have with eliminating waste products of protein metabolism.
But, for the healthy, active individual, they actually stand to benefit from higher protein intakes, particularly if they are interested in building muscle or dieting for fat loss.
High-Protein Diets and Bone Health
Following kidney damage, the second most common myth surrounding high-protein diets is that it can lead to osteoporosis.
The hypothesis holds that protein increases the acidity of your body. In order to prevent the body from becoming overly acidic, it must remove calcium from bone to neutralize the acid. 
However, this calcium-leaching effect only occurs over the short term and does not lead to long term decalcification of bone. 
In fact, longer-term studies show that not only is bone healthy not threatened by high-protein diets, it actually led to improvements in several hormones (including IGF-1) that support bone health. 
Furthermore, additional research notes that higher protein intakes improve your bone density, lower fracture risk, boost IGF-1 levels, and enhance lean mass, all of which serve to support bone health. [20,21,22,23]
Additionally, a comprehensive review of the literature in 2016 led by Dr. Stu Phillips found that:
“Despite persistent beliefs to the contrary, we can find no evidence-based link between higher protein diets and renal disease or adverse bone health.” 
The National Osteoporosis Foundation carried out a systematic review and meta-analysis, including 16 randomized-control trials and 20 cohort studies, and concluded that high protein intakes do not weaken or harm bones. Researchers did note that there was a positive trend towards higher protein intakes improving bone health, though. 
Another review was carried out in 2018, this time by the International Osteoporosis Foundation.  Some key findings from the narrative review include:
Bone mineral density is positively associated with dietary protein intakes
Higher protein intakes lead to a modestly decreased risk of hip fracture, provided calcium intake is sufficient.
Dairy products, which combine protein and calcium, beneficially impact calciotropic hormones, bone turnover markers, and bone mineral density.
No direct evidence was found between the acid load of higher protein intakes and the progression of osteoporosis, compromised bone strength, or fragility fractures.
Researchers went onto state in the conclusion of the review:
“With intakes above the current RDA, dietary protein is rather beneficial in reducing bone loss and fracture risk, especially at the hip, provided calcium intakes are adequate. Insufficient dietary protein intakes may be a much more severe problem than protein excess.” 
And, if you’ve ever been told that dairy is bad for your bones (due to it being acidic), researchers also addressed that in the 2018 review when they stated:
“Protein and calcium combined in dairy products have beneficial effects on calciotropic hormones, bone turnover markers and BMD. The benefit of dietary proteins on bone outcomes seems to require adequate calcium intakes.” 
Seeing as dairy contains both highly bioavailable protein and calcium, it seems like you can keep drinking your moo juice and whey protein shakes without concern that your bones are being slowly whittled away.
Consider another myth about high-protein diets busted.
How Much Protein to Maximize Muscle Growth?
Now that we’ve sufficiently put to rest the idea that high-protein diets rot your kidneys and weaken your bones, let’s turn our attention to one of the main reasons an individual would consume a diet high in protein -- muscle growth.
As you probably know, muscles are made of protein, and intense exercise breaks down muscle. To repair the damaged muscle fibers, your body needs amino acids, which they can obtain from dietary protein.
The next question becomes -- how much protein do you need to maximize the muscle-building process?
Well, the truth is you need a considerable amount more than the RDA for protein (which is a paltry 0.8g/kg/day), and let’s be honest the RDA is not based on the weightlifting population. It’s based off of the overweight couch potato who has minimal physical activity.
But, you might not need quite as much as you think.
A recent meta-analysis spearheaded industry experts Brad Schoenfeld, Alan Aragon, and Eric Helms set out to determine the “optimal” amount of protein an individual should consume to maximize the protein synthetic response.
Pooling data from 49 different studies with 1,863 participants, Schoenfeld and friends determined that the optimal intake of dietary protein for resistance-trained individuals (i.e. weightlifters) is somewhere between 1.6-2.0 g/kg/day.
Beyond this amount, researchers have documented little to no additional benefits in terms of increased lean mass gains, which means consuming above 1g/lb of bodyweight isn’t necessarily better from a muscle building standpoint, at least.
Now, if you are in a fat loss phase, you do stand to retain more lean muscle while dieting when consuming a higher protein diet. A review paper by Dr. Eric Helms noted that the recommended protein intake for lean individuals engaged in a fat loss phase be somewhere in the neighborhood of 2.3-3.1g/kg/day (~1.05-1.4g/lb/day). 
The Bottom Line on High-Protein Diets and Health
At the end of the day, the preponderance of evidence indicates that high-protein diets do not adversely affect bone, liver, or kidney health and function. If anything, an individual stands to gain more from higher protein intakes, and diets high in protein have numerous beneficial effects on body composition, enhancing fat loss and increasing muscle mass. Higher protein diets are also associated with greater feelings of satiety and increased calorie expenditure.
Essentially, there really is no downside to erring on the side of higher protein intakes in healthy individuals. The idea that high-protein diets being detrimental to renal function and bone health in healthy individuals are not supported by scientific literature.
If you have impaired kidney function or chronic kidney disease, it would behoove you to monitor protein intake under the guidance of a well-qualified physician or nephrologist.
Bottom line -- Consuming a diet high in protein is a great way to enhance body composition and stay strong, durable, and resilient as you age. Provided you’re healthy, high protein diets will not have negative consequences on health, wellness, or function.
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