A 2018 analysis in the American Journal of Clinical Nutrition looked at what 57,980 Americans ate between 2001 and 2014, using federal survey data. Protein made up 14 to 16 percent of their calories. In every age, sex and race or ethnicity group the researchers examined, average intake sat above the Estimated Average Requirement.
Two groups came closest to falling short. Among girls aged 14 to 18, 11 percent were below that requirement. Among non-Hispanic Black men aged 71 and over, 13 percent were. Fewer than 1 percent of any group exceeded the upper end of the acceptable range for protein as a share of calories.
That is the setting the protein powder aisle sits in, and it reframes the question most shoppers arrive with. The useful question is usually not which powder, but whether a powder.
How much protein Americans eat, and against what benchmark
The 2018 analysis, by Berryman and colleagues at the US Army Research Institute of Environmental Medicine, used the National Health and Nutrition Examination Survey. Usual daily protein intake ranged from 55.3 grams in children aged 2 to 3 up to 88.2 grams in adults aged 19 to 30. Measured against body weight, it ran from 1.10 grams per kilogram of ideal body weight in adults 71 and over to 3.63 in the youngest children. The authors summarize it in one line: “The majority of the US population exceeds minimum recommendations for protein intake.” The work was federally funded.
One distinction changes how you read every number above. The Estimated Average Requirement is the figure built to judge groups, set at the level that meets the needs of half a population. The Recommended Dietary Allowance sits above it, deliberately high enough to cover nearly everyone, which means any individual’s own requirement is almost certainly lower. The RDA is not a floor you are failing to reach.
Article 670 covers the 2025-2030 Dietary Guidelines protein recommendations in detail.
The reference figures, and the table that has not moved since 2005
The Office of Dietary Supplements reports the RDA for protein as 0.8 grams per kilogram of body weight per day for healthy adults, and reports that more recent data suggest athletes require 1.2 to 2.0 grams per kilogram a day. Those are published population figures from a federal office, not a target this site is setting for anyone. The Food and Nutrition Board has set no Tolerable Upper Intake Level for protein.
Here is the part that rarely makes it into the marketing. A 2025 systematic review in the American Journal of Clinical Nutrition by Burstad and colleagues, conducted for the federal reference-intake process, states plainly that protein intakes are set by Dietary Reference Intakes published in 2005 and not updated since. The team screened 11,408 studies and found 66 eligible, 45 of them at low or moderate risk of bias, and concluded that research is limited across the life cycle, particularly in pregnancy, lactation, infancy, childhood and adolescence. They also report something to read alongside every protein number here: for adults aged 19 to 50, the underlying requirement studies for protein and most individual indispensable amino acids enrolled males only.
Heavy metals: what was found, and who paid for the finding
This is the part of the subject with the most heat and least agreement, and no party reporting on it is disinterested.
Two product surveys set it off. Consumer Reports tested 15 protein powders and found the average heavy-metal content of three servings a day exceeded limits proposed by the US Pharmacopeia. A follow-up reported that 40 percent of 133 products had elevated levels. Both are described inside a peer-reviewed risk assessment in Toxicology Reports in 2020; the originals were not retrieved for this article.
The most widely shared testing is a January 2025 whitepaper from the Clean Label Project. It tested 160 protein powders from 70 brands said to represent 83 percent of the market, selected from Nielsen and Amazon best-seller lists plus top natural and organic products, with Ellipse Analytics running heavy metals by ICP-MS.
The benchmark matters as much as the numbers. The report compares results against California’s Proposition 65 levels and against federal or state regulatory limits. Its headline findings: 47 percent of products exceeded at least one federal or state safety limit, and 21 percent were over twice Prop 65 levels. Chocolate powders fared worst, with 65 percent over Prop 65 for lead, roughly four times the lead of vanilla and about 110 times the cadmium. Plant-based powders carried about three times the lead of whey-based ones, and organic products about three times the lead and twice the cadmium of non-organic.
The report does not state who funded it. It promotes the organization’s own certification program and names one protein company holding that certification.
The risk assessment that read the same data differently
The 2020 Toxicology Reports paper, by Bandara, Towle and Monnot, took the concentrations from those surveys and ran a conventional exposure assessment, using EPA reference doses for arsenic and cadmium, EPA’s screening level for mercury, and EPA’s Adult Lead Methodology to model blood lead against the CDC guidance value of 5 micrograms per deciliter.
Every product came in with a hazard index below 1, meaning no increased health risk by that method. The highest values, approaching 1, were in mass-gain powders; the lowest were in whey. All modeled blood lead levels fell below the guidance value, with background environmental exposure the main contributor.
All three authors were at Cardno ChemRisk, a consultancy that works for industry and in litigation, and the paper’s funding statement was not retrieved. That affiliation does not make the arithmetic wrong, and it is printed on the paper for a reason.
The critics, and what they are
Three named critics pushed back on the 2025 report in trade coverage, and all three lead supplement industry trade associations. Andrea Wong of the Council for Responsible Nutrition argued that detecting a contaminant does not by itself equate to a health risk. Daniel Fabricant of the Natural Products Association called the report a sham and said his group was refused the underlying data. Duffy MacKay of the Consumer Healthcare Products Association made the sharpest technical point: Prop 65 levels are a labeling trigger rather than a safety threshold, and the appropriate reference points are FDA’s interim reference level for dietary lead in adults, 12.5 micrograms a day, and the US Pharmacopeia’s 10 micrograms a day.
That FDA figure checks out independently. A 2020 paper in Regulatory Toxicology and Pharmacology written by FDA scientists confirms the agency set interim reference levels of 3 micrograms a day for children and 12.5 for women of childbearing age, each corresponding to a blood lead level of 0.5 micrograms per deciliter, and concluded that using the 12.5 figure as a benchmark is one way FDA will work to reduce adult dietary lead intake.
Clean Label Project’s executive director, Jaclyn Bowen, defended the Prop 65 benchmarks as among the strictest consumer protection standards available and confirmed the organization runs a voluntary certification program whose revenue funds its research and advocacy.
So: an advocacy organization that sells certifications on one side, three trade associations on the other, and a risk assessment by a litigation-facing consultancy in the middle. Read every figure here with its author attached. Contamination in herbal products is covered in article 315.
The label number comes from nitrogen, not from protein
Most people assume a laboratory measures protein. It usually measures nitrogen and does arithmetic.
Federal labeling rules make this explicit. Under 21 CFR 101.9(c)(7), “Protein content may be calculated on the basis of the factor 6.25 times the nitrogen content of the food,” using an approved method of analysis, unless the official procedure calls for a different factor. The 6.25 comes from the fact that protein averages roughly 16 percent nitrogen.
The gap that opens up is simple. Any nitrogen-rich ingredient reads as protein. Free amino acids such as glycine or taurine, which cost far less than whole protein, push the measured nitrogen up without delivering the mix of amino acids a body builds muscle from. That practice is known as amino acid spiking, or nitrogen spiking.
The same regulation contains a quality measure that is mostly invisible to shoppers. For foods intended for adults and children four and older, a protein digestibility-corrected amino acid score below 20 percent triggers either a corrected percent Daily Value or a statement that the food is not a significant source of protein. Otherwise that corrected statement is optional unless the product makes a protein claim, so a gram count can be nitrogen-derived while the quality correction never appears on the panel.
Direct evidence that spiking happens comes from two peer-reviewed analyses in Medicine, published in 2024 and 2025 by Philips and colleagues. The first found that most products did not meet their labeled protein content while some exceeded it, which the authors flag as a spiking concern. The second compared 18 medical-pharmaceutical and 16 nutraceutical whey powders and detected taurine-based nitrogen spiking in 89 percent of the pharmaceutical products against 12.5 percent of the nutraceutical ones, with 83 percent of the pharmaceutical powders mislabeled by more than 5 percent either way.
Two caveats carry equal weight. Both studies tested the Indian market, so the percentages are not US figures. And both are unusually transparent about money: the 2024 paper calls itself self-funded in its own title, and the 2025 study was publicly crowd-funded.
On US enforcement, the honest answer is that we found none. A targeted search for an FDA warning letter, an FTC action or a state attorney general action on nitrogen spiking returned nothing but retailer pages and marketing content. That is a gap in the public record as we could document it, not evidence that nothing has happened.
Whey, casein and plant protein: what is measured, and what changes
Short laboratory studies and long training studies answer different questions, and conflating them is where most of the marketing lives.
In a 2014 study in the American Journal of Clinical Nutrition, Witard and colleagues gave 48 resistance-trained young men 0, 10, 20 or 40 grams of whey isolate after leg exercise and tracked muscle protein synthesis with a labeled amino acid. Synthesis rose 49 percent at 20 grams and 56 percent at 40 grams above the zero condition, and above 20 grams the surplus went into amino acid oxidation and urea production. A 2011 study in the American Journal of Physiology compared labeled whey against labeled casein after heavy resistance exercise: whey produced larger insulin and branched-chain amino acid responses, and myofibrillar protein synthesis rose equally for both.
Over months of actual training, the differences mostly wash out. A 2020 trial compared whey isolate with soy isolate matched for leucine content across 12 supervised weeks in 48 completers: lean body mass rose 1.54 kilograms and leg extensor peak torque rose 40.27 Newton-meters, with no differences between groups. A 2025 randomized trial in 44 untrained young men compared a soy and pea blend with whey across 12 weeks of supervised periodized training and found significant gains in both groups and none between them. A 2018 meta-analysis of nine studies and 266 participants concluded that soy produces gains similar to whey; its first author’s printed affiliation is a private nutrition consultancy, not a university.
Two results point the other way. A 2013 trial ran 63 untrained adults through 96 supervised workouts over about nine months, comparing isocaloric carbohydrate, whey and soy. Lean body mass gains were 3.3 kilograms for whey, 2.3 for carbohydrate and 1.8 for soy, with whey significantly ahead of both. A 2024 network meta-analysis of 78 trials and 5,272 older adults ranked whey first among six sources for muscle mass, handgrip strength and walking speed.
The most awkward finding for everyone is recent. A 2026 trial in the Journal of Nutrition gave 45 healthy men averaging 69 years old either 20 grams of a soy and pea blend, the same blend plus leucine, or 20 grams of whey. Whey raised plasma essential amino acids the most, as expected. Muscle protein synthesis rates were identical across all three groups and were not raised above fasting values at all. Three of the authors are employed by Danone Research and Innovation, which sells protein products.
The fair summary: the acute plasma differences between sources are real and measurable. Over 12 weeks to nine months of supervised training, matched for leucine or total protein, most head-to-head trials find no difference, while one long trial and one network meta-analysis favor whey. Both are legitimate and they disagree. Collagen as a protein source is covered in article 338.
Kidneys: two different questions again
For healthy adults, two meta-analyses of overlapping literature reach opposite conclusions.
A 2018 analysis in the Journal of Nutrition by Devries and colleagues pooled 28 trials and 1,358 participants, defining high protein as at least 1.5 grams per kilogram, or 20 percent of energy, or 100 grams a day. Post-intervention filtration rate was slightly higher with high protein, a difference the authors call trivial, and the change in filtration from baseline did not differ at all. Their conclusion is that high protein intakes do not adversely influence kidney function on GFR in healthy adults, with an unclear risk of selection bias in the included trials.
A 2014 analysis in PLoS One by Schwingshackl and Hoffmann pooled 30 studies and 2,160 subjects without kidney disease and found high-protein diets raised glomerular filtration rate by 7.18 mL/min/1.73m², serum urea by 1.75 mmol/L and urinary calcium excretion by 25.43 mg per 24 hours, all at p below 0.001. Their conclusion: given the high risk of kidney disease among people with obesity, weight-reduction programs recommending high-protein diets, especially from animal sources, should be handled with caution.
The best-controlled single experiment sits between them. The NIH-funded OmniHeart feeding trial, published in the American Journal of Kidney Diseases in 2013, fed 164 healthy adults with prehypertension or stage 1 hypertension three diets for six weeks each, with all meals supplied and body weight held constant. Shifting protein from 15 to 25 percent of energy raised cystatin C-based estimated filtration by about 4 mL/min/1.73m². The authors say whether long-term high-protein eating leads to kidney disease is uncertain.
A 2018 systematic review in Advances in Nutrition split the same way: of 13 randomized trials, 8 found significantly higher filtration at higher protein intakes and 5 did not, all consistent with normal kidney function. One of its three authors is affiliated with the National Cattlemen’s Beef Association.
Existing chronic kidney disease is a different question entirely, and the research above does not speak to it. In kidney disease, total protein intake is part of a treatment plan and higher protein is not appropriate. That figure is set by the clinician managing the condition, not by a label. If a blood test has shown reduced kidney function, or a clinician has told you to watch your protein, the daily total belongs in that care conversation rather than in the supplement aisle.
New York’s law leaves protein powders out, with one exception
New York’s Chapter 558 of 2023, the first state law barring sales of weight-loss and muscle-building supplements to anyone under 18, writes protein out of its own definition. The covered category expressly does not include protein powders, protein drinks or foods marketed as containing protein.
The exclusion is not unconditional. It stops applying if the product contains an ingredient other than protein that would, on its own, qualify as a dietary supplement for weight loss or muscle building. A plain protein powder is outside the law. A protein powder with a muscle-building ingredient blended in can be pulled back inside it.
California’s AB 2030, signed September 28, 2026, uses the same marketing-based approach. Article 339 covers how these statutes treat specific ingredients and the First Amendment challenge the Supreme Court declined to hear on October 5, 2026.
Five checks that tell you something
Most protein-powder advice circulates without saying what each item is evidence of. Here is what each one supports.
Your own food intake, before anything else. The survey data says most Americans already exceed the minimum, and the gap people imagine is usually larger than the one the data shows.
The gram count is a nitrogen measurement. It tells you how much nitrogen was in the sample, not which amino acids delivered it.
Whether a corrected protein percent Daily Value appears. The rule makes that correction optional except when a protein claim is made, so its presence is informative and its absence is normal.
What a third-party mark covers. Certification programs test for specific things, not everything. Article 326 explains what each one checks.
Flavor and base, not brand. In the 2025 testing, chocolate against vanilla, plant against whey and organic against conventional all moved in directions most shoppers would not predict, and those categories cut across every brand.
What the protein numbers settle
Across federal survey data covering nearly 58,000 people, average protein intake exceeds the Estimated Average Requirement in every demographic group measured, with two groups nearest the line: teenage girls and Black men over 70. A powder is a convenient delivery format for a nutrient most people already get, not a different nutrient. Across trials running 12 weeks to nine months, source matters less than the marketing suggests, though two good studies disagree. The contamination picture has no neutral referee, and the reference figures underneath it all come from a 2005 table.
The single most useful thing to carry: the protein number on the panel is the output of a nitrogen test multiplied by 6.25. And the one group for whom daily protein is a clinical quantity rather than a shopping decision is people with kidney disease, where the number is set in a treatment plan and nowhere else.
Sources
- National Institutes of Health, Office of Dietary Supplements. “Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Health Professionals.” ods.od.nih.gov
- U.S. Government, Electronic Code of Federal Regulations. “21 CFR 101.9 – Nutrition labeling of food (paragraph (c)(7), protein).” ecfr.gov
- The American Journal of Clinical Nutrition (PubMed). “Berryman CE, Lieberman HR, Fulgoni VL, Pasiakos SM. "Protein intake trends and conformity with the Dietary Reference Intakes in the United States: analysis of NHANES, 2001-2014." 2018. DOI: 10.1093/ajcn/nqy088.” doi.org
- The American Journal of Clinical Nutrition (PubMed). “Burstad KM et al. "Evaluation of dietary protein and amino acid requirements: a systematic review." 2025. DOI: 10.1016/j.ajcnut.2025.04.017.” doi.org
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- Clean Label Project. “Protein Powder Study White Paper, January 6, 2025.” cleanlabelproject.org
- NutraIngredients-USA. “Clean Label Project puts protein powder under the microscope, critics call the report misleading.” nutraingredients.com
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- Medicine (Baltimore) (PubMed). “Philips CA et al. "The Citizens Protein Project 2: crowd-funded analysis of popular whey protein supplements in India." 2025. DOI: 10.1097/MD.0000000000045970.” doi.org
- The American Journal of Clinical Nutrition (PubMed). “Witard OC et al. "Myofibrillar muscle protein synthesis rates subsequent to a meal in response to increasing doses of whey protein at rest and after resistance exercise." 2014. DOI: 10.3945/ajcn.112.055517.” doi.org
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- International Journal of Sport Nutrition and Exercise Metabolism (PubMed). “Messina M, Lynch H, Dickinson JM, Reed KE. "No Difference Between the Effects of Supplementing With Soy Protein Versus Animal Protein on Gains in Muscle Mass and Strength in Response to Resistance Exercise." 2018. DOI: 10.1123/ijsnem.2018-0071.” doi.org
- Journal of the American College of Nutrition (PubMed). “Volek JS et al. "Whey protein supplementation during resistance training augments lean body mass." 2013. DOI: 10.1080/07315724.2013.793580.” doi.org
- Journal of the International Society of Sports Nutrition (PubMed). “Santini MH et al. "Similar effects between animal-based and plant-based protein blend as complementary dietary protein on muscle adaptations to resistance training." 2025. DOI: 10.1080/15502783.2025.2568047.” doi.org
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- The Journal of Nutrition (PubMed). “Kuin LM, van Loon LJC et al. "Ingestion of 20 g of a Plant-derived Protein Blend With and Without Added Leucine or Whey Protein Does not Increase Muscle Protein Synthesis Rates in Older Males." 2026. DOI: 10.1016/j.tjnut.2026.101789.” doi.org
- The Journal of Nutrition (PubMed). “Devries MC, Phillips SM et al. "Changes in Kidney Function Do Not Differ between Healthy Adults Consuming Higher- Compared with Lower- or Normal-Protein Diets." 2018. DOI: 10.1093/jn/nxy197.” doi.org
- PLoS One (PubMed). “Schwingshackl L, Hoffmann G. "Comparison of high vs. normal/low protein diets on renal function in subjects without chronic kidney disease." 2014. DOI: 10.1371/journal.pone.0097656.” doi.org
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- New York State Senate. “Senate Bill S5823, 2023-2024 Legislative Session (Chapter 558 of 2023).” nysenate.gov
- Haynes and Boone, LLP. “New California Law Bans Sale of Diet Pills and Certain Supplements to Minors.” haynesboone.com