Tension has been brewing in the world of nutrition. The subject of the dispute? Protein — or more precisely, protein requirements, and journalists, scientists, government officials, and health influencers are all weighing in.
I’m certainly no stranger to the fray, having discussed on numerous occasions my belief (and the research behind it) that the U.S. Recommended Dietary Allowance (RDA) for protein is too low for optimizing health. In fact, some news outlets have cast me as a “poster man” for this position, though I’m clearly not alone. The sheer variety of protein-fortified foods that have made their way onto grocery store shelves attests to the growing number of individuals seeking to increase their intake of this macronutrient.
Yet this trend has prompted some backlash. Many in mainstream media and social media have denounced the protein boom as a “marketing scam,” claiming that the RDA is sufficient for most individuals and warning against alleged dangers of high-protein diets.
As we often see in nutrition, proponents of these opposing positions typically express their respective views with such passion and confidence as to seem quite convincing. But when it comes to finding scientific truth, passion and confidence carry little weight. The currency that matters is data — specifically, data that are acquired through sound methodology and are interpreted appropriately, with nuance, for the question at hand. And when we take a critical look at the data on protein and human health, the arguments against higher protein intake come out bankrupt.
Is the RDA protein recommendation “adequate”?
A common theme echoed by protein skeptics has been the assertion that the U.S. RDA for protein — currently set at 0.8 grams of protein per kilogram of body weight per day, or just under 0.4 g per pound of body weight per day — is “adequate for most people’s basic needs.” I, on the other hand, have stated on many occasions that I recommend double this amount — around 1.6 g/kg and up to 2.2 g/kg (0.8–1.0 g/lb). Why the discrepancy? To understand this, we first need to spend a little time breaking down exactly what the RDA means and, more importantly, where it came from.
Origins of the protein RDA can be traced back to around the turn of the 19th to 20th century. Because protein is the only macronutrient that contains the element nitrogen (which the body uses for synthesis of amino acids and nucleic acids), researchers at this time sought to establish the level of protein required to maintain an equilibrium between nitrogen inputs (i.e., dietary protein) and nitrogen excretion (primarily through urine). If the amount of nitrogen excreted exceeds the amount ingested, then the body is in a nitrogen deficit and must break down muscle and other tissues to meet its needs — an unsustainable solution. However, if inputs and outputs are evenly matched, then intake is sufficient to maintain tissue integrity and support basic survival requirements indefinitely. (At least, intake of nitrogen in general is sufficient, though this does not account for intake requirements for specific amino acids.)
From this perspective, the current RDA could indeed be regarded as “adequate,” at least for some fraction of the population. Nitrogen balance experiments throughout the 20th century have generally reported daily protein requirements roughly equivalent to the current RDA or even slightly lower. Thus, the 0.8 g/kg recommendation was adopted as a modestly inflated value to account for likely variation across individuals.
Though this approach may seem sound, many nutrition experts have pointed out a number of significant flaws in the logic and methodology that gave rise to the RDA. For instance, some percentage of nitrogen is lost through sweat, making it very difficult to fully account for all nitrogen excretion. Further, these protein requirements are based on high-quality protein with optimal amino acid ratios and high bioavailability (e.g., eggs or milk protein), whereas protein from plant-based sources tend to be absorbed more poorly and are less capable of stimulating anabolic processes in the same manner as animal proteins. As a result, the RDA will be insufficient for maintaining nitrogen balance for those relying on plant-based proteins.
But the most glaring fault with the research on which the RDA is based is its reliance on a very narrow sampling of the population. The studies were typically conducted in young men (often Caucasian college students) who were generally healthy and lean (some of the landmark work was based on a “standard” male body weight of 150 lbs — what I weighed when I was about 15 years old) and often physically inactive. Even the tiny “buffer” that was added to the RDA to account for interindividual variability was only based on variability within these narrow study cohorts (covering 1-2 standard deviations from the mean). It did not in any way account for the much greater variability across the full U.S. population, which is largely composed of older adults who are known to require significantly higher levels of protein intake than individuals in their 20s, due to anabolic resistance. The RDA also fails to consider other common cases where protein requirements increase, such as during pregnancy, breastfeeding, childhood development, or recovery from injury or illness, let alone the added protein needs of those who engage in regular resistance training. In other words, the RDA is adequate for the body’s functional basic needs if you are a diminutive, fairly sedentary, young adult in otherwise good health who is not attempting to add muscle to your frame. If you don’t fall into that group, good luck…
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Since when does “adequate” equal “optimal,” anyway?
Let’s say you are indeed one of the lucky ones who can get by on just 0.8 g/kg of protein every day. Is “getting by” really a worthy goal? Do we tell our kids to be happy with a D+ when they could have gotten an A or A- with a bit of work? Of course not, and the reason is simple: adequate does not necessarily equate to optimal.
I, along with many experts in nutrition, exercise science, and aging research, have long espoused the notion that building and maintaining muscle mass is vital for retaining functional capacities as we age and for living as long and as healthy a life as possible. Skeletal muscle is the organ responsible for absorbing the most glucose and is therefore vital for maintaining glucose homeostasis. Given that dysregulated glucose homeostasis sits squarely at the center of the diseases that kill most people in the developed world (think cardiovascular disease, most cancers, Alzheimer’s disease, type 2 diabetes), it’s impossible to argue that even if muscle did nothing else for you, the simple fact that it is key to regulating glucose seems reason enough to put on muscle. Of course, add to this the fact that quality of life matters at least as much, if not more, than length of life to most of us, and you come to an inescapable conclusion: if you want to live longer and live better (avoiding sarcopenia — i.e., low muscle mass — might be the single most important step here), you’d better devote a lot of time and energy to building muscle.
[To dive into the Mount Everest of evidence supporting these assertions would be beyond the scope of this piece, but you can refer to past content, such as my recent AMA episode on muscle mass, earlier AMAs on the links between muscle and longevity and quality of life, and numerous newsletters on this subject.]
If we accept this fact, and I can’t think of logical argument by which we can’t, then there is simply no question that optimal protein intake is much higher than the current RDA, just like having a VO2 max at the 90th percentile of the population is better than having one at the 25th percentile if you want to live longer, or having a HbA1c of 5.1% is better than having one of 5.6% (i.e., both are below the cutoff of even pre-diabetes, but the former is still associated with lower all-cause mortality). Protein is required not only for preventing muscle loss but also for stimulating and providing the raw materials for muscle growth, and countless randomized trials and meta-analyses have consistently converged on a protein intake of around 1.6-2.2 g/kg/day — more than double the RDA — as the optimal level to maximize muscle protein synthesis (MPS).
Even many critics of the protein boom concede that existing research supports the idea that the RDA is too low to support maximal muscle growth, though they question the degree to which intake needed to be increased. In an April article from the New York Times, the author argues that 1.5x the RDA is enough to maximize muscle gains, citing a trial showing no difference between groups given 1.5x the RDA and 2.0x the RDA. However, it’s worth pointing out that this trial, which involved resistance training in conjunction with the 10-week diet intervention, was conducted in untrained adults. Starting from low baseline strength, the baseline protein requirements in these individuals would have also been relatively low, so even modest increases above the RDA would have been sufficient to support the excess needed to build more muscle. If this study had, by contrast, been conducted in those who already had a moderate amount of muscle and/or people who were not newcomers (read: hyper-responders) to resistance training, protein requirements for maintenance of that baseline level of muscle would have been significantly higher, and thus, even greater increases above the RDA would be necessary to support further muscle gains. Indeed, most analyses indicate that MPS and muscle hypertrophy don’t start to plateau until at least 1.6 g/kg/day of protein intake, and the threshold is likely higher with increasing age, increasing baseline muscle mass, or lower protein quality (i.e., plant proteins, as discussed earlier).
Can you have “too much” protein?
We’ve now presented evidence that the RDA is too low for optimal health and, for many groups, is too low even for maintaining basic nitrogen equilibrium. It therefore stands to reason that you ought to shoot for a level of intake somewhere above that of the RDA, ideally at least 1.6 g/kg/day (~0.8 g/lb/day). But is it possible, as many critics claim, to aim too high? Can too much protein be dangerous?
Dr. David B. Allison, the current Chief of Nutrition and Director of the Children’s Nutrition Research Center at Baylor College of Medicine, recently addressed this very question in a review paper published earlier this summer. As he explains, we must again begin with a close examination of the origins of the belief in the so-called “dangers” of a high-protein diet. This strangely, pathologically persistent idea stemmed mainly from century-old anecdotal reports of “poisoning” among individuals consuming very large amounts of meat. These reports were cited by other researchers, who were then cited by others, who were then cited by others until the dubious anecdotes evolved into the widely accepted — but ultimately unproven — belief that too much protein can be broadly harmful to health. (Of note, no cases of such “meat poisoning” have been reported since the advent of regulatory oversight of food safety, even with the growing popularity of “carnivore” diets in the present day.)
Today, much of the fear surrounding the dangers of high protein intake concerns its potential negative impacts on the kidneys due to increased urea production. Indeed, such effects have been shown in a handful of studies in mice, but human data have failed to substantiate these findings, including at very high levels of intake (more than 3 g/kg/day). Now, last time I checked, we were the species of interest, not our furry little four-legged rodent friends. According to a Cochrane review, even among individuals with existing chronic kidney disease, moderately restricting protein does not appear to significantly reduce risk of death or disease progression.
Other concerns regarding the possibility of “too much” protein include effects on cancer risk and aging, but these worries have even less grounding in evidence than fears over kidney function. I’ve discussed both of these subjects in depth in previous articles, but in essence, these concerns arose primarily from hypothetical mechanistic links that have not stood up remotely to actual empirical inquiry.
Finally, some argue that reducing protein intake can improve metabolic health. This view partially stems from observational data linking meat intake with type 2 diabetes, though as I’ve explained so often in the past, it is much more likely that these associations reflect the influence of countless confounding variables than a true, causal link between meat (let alone protein per se) and metabolic dysfunction. Still, many protein nay-sayers point out that the alleged metabolic benefits of protein restriction are also supported by results from randomized trials, and given that randomized trials are regarded as the “gold standard” for determining the health effects of a given intervention, it’s worth taking a moment to examine these data more closely.
One commonly cited study is a 2016 trial involving 38 overweight or mildly obese men randomized to protein restriction (~7–9% of total calories from protein) or their usual diet (~10–14% calories from protein). After an average of about 43 days on the respective diets, those in the protein restriction group had decreased in total body weight (−2.62±2.18 kg, or a loss of ~5.8 lbs), fat mass (−1.37±1.55 kg, or a loss of ~3.0 lbs), and fasting glucose levels (−7.00±9.33 mg/dL), whereas the control group had not changed significantly from baseline in any of these metrics. Yet although these results seem to suggest that lower protein intake improves metabolic health, they are not as convincing as they might first appear. The changes were small and highly variable (as evidenced by the high standard deviations), raising questions about their reliability and clinical significance. More importantly, the results indicate that roughly half of the weight lost by protein-restricted participants came from lean mass. While some lean loss is inevitable with total weight loss, a more typical ratio (e.g., seen with GLP-1 receptor agonist drugs or overall calorie restriction) is approximately 25-30% lean mass loss,20 whereas a loss of 50% lean mass is far more likely to have a net negative impact on overall body composition and metabolic health, given the metabolic functions of muscle described earlier.
But perhaps my favorite piece of “evidence” cited for the metabolic benefits of protein restriction is a 2022 trial in 21 individuals with metabolic syndrome randomized to protein restriction or overall calorie restriction. Why is it my favorite? Because it reminds us of the vital role that editors and peer-review play (or rather, are supposed to play) in guarding against dissemination of faulty data. The numbers in this study quite literally don’t add up. The reported daily intakes of total calories and calories from protein are mathematically inconsistent with the level of protein intake they report in terms of grams per kilogram of body weight, so we have no idea how many calories these participants were really consuming, nor how much protein. How the reviewers didn’t catch this is anyone’s guess, but it effectively prohibits any meaningful interpretation of results.
If the science on protein is clear, why are recommendations still so low?
This past spring, I was interviewed for the New York Times Well Festival, and as the discussion eventually turned to protein, the interviewer framed my views on protein requirements as being contradictory to “scientific consensus.” After all, the RDA has remained at 0.8 g/kg/day for nearly 40 years, so there must be a reason, right?
In preparing this piece, our goal has never been to promote some sort of protein iconoclast agenda. Quite the opposite — we have actively sought evidence to contradict our incoming perception that the RDA is too low, and we have attempted to share the strongest of those results throughout this article, along with our reasoning as to where and why they fall short. We have made every effort to be thorough in our evaluation of the evidence — and we certainly aren’t alone in our conclusions. Indeed, the shortcomings of the RDA have long been acknowledged by both government agencies and the scientific community.
The fact is that the RDA was never intended as a broadly applicable guideline for optimal protein intake. It has always been reported as a minimum that must be significantly increased for children, older adults, active individuals, and women who are pregnant or breastfeeding. Somehow, those adjustments have been lost as part of the popular discourse about protein.
Further, the flaws in research that gave rise to the RDA are now widely recognized, including by U.S. government agencies. Nitrogen balance studies are no longer regarded as an acceptable basis for estimating true protein requirements, and nutrition researchers are increasingly calling for the use of alternative methods to serve as the foundation for future RDA editions. According to Dr. David Klurfeld, a nutrition scientist and long-time leader of nutrition research for the U.S. Department of Agriculture (USDA), the FDA now primarily relies on Protein Digestibility Corrected Amino Acid Score (PDCAAS) and, increasingly, Digestible Indispensable Amino Acid Score (DIAAS) — both of which critically account for protein quality (i..e, amino acid ratios) and digestibility, in contrast to the RDA — in evaluating claims with respect to protein and in setting daily values for protein. Indeed, the National Academies of Science, Engineering, and Medicine (NASEM) is currently re-evaluating RDAs and dietary reference intakes (DRIs) for protein and other nutrients in light of evidence supporting an increase to existing recommendations.
Put simply, the “scientific consensus” supporting the current RDA is anything but.
Are you getting enough protein?
Of course, all of the above leads to the one question that matters to each of you as readers: are you getting enough protein? Some popular press outlets would argue that the answer is probably “yes,” noting that “the idea that Americans don’t eat enough protein … is a lie.” Yet this perspective is based on data showing that the majority of Americans meet the RDA, which as we’ve seen, is insufficient for many individuals’ basic functional needs, even according to the guidelines themselves. These very same data reveal that the majority of Americans are not achieving a level of intake that would best facilitate muscle mass gains and optimize health. So I encourage you to evaluate your own dietary habits — including the type of protein and timing of intake — to ensure that you’re supplying your body with the building blocks it needs to become stronger and healthier.
Protein — and nutrition in general — is just one part of that larger goal. And toward that end, we must not get so wrapped up in online debates that we confuse passionate tribalism for scientific fact or lose sight of what truly constitutes rigorous evidence — because ultimately, it’s evidence and reason that will lead us to the answers that make a difference for our own health and longevity. And in the case of protein, the science speaks for itself.
We would like to acknowledge Dr. David B. Allison and Dr. David Klurfeld for the invaluable information, insights, and feedback they provided as we drafted this article. For footnotes and citations, please see the full piece, which was originally published on peterattiamd.com.
Peter Attia, MD, is the host of The Peter Attia Drive podcast and founder of Early Medical, a medical practice that applies the principles of Medicine 3.0 to patients with the goal of simultaneously lengthening their lifespan and increasing their healthspan.
