How Protein Requirements Are Set: RDA, EAR, AMDR, Nitrogen Balance and IAAO
How official protein figures such as the RDA, EAR and AMDR are worked out from nitrogen balance and amino acid oxidation studies, why methods disagree, and where the debate stands.
Content last updated . This page has not been medically reviewed.
What the terms mean
The table gives each term, what it means, and one example with the population, body and year. The US Daily Value for protein on labels is covered in Protein Quality Scores. Grams per kilogram (g/kg), grams per day and percent of calories are different units and should not be mixed; Protein Units Explained shows how they relate.| Term | What it means | Example (population, body, year) |
|---|---|---|
| EAR (estimated average requirement) | For US and Canadian adults, the lowest continuing intake that reaches nitrogen equilibrium (zero balance) [1] | Adults 19 and over: 0.66 g/kg/day. Health Canada table of the 2005 US and Canadian values, page dated 2025 [2] |
| RDA (recommended dietary allowance) | Set about two standard deviations above the EAR, so it meets the needs of nearly all (97 to 98 percent) healthy people [1] | Adults 19 and over: 0.80 g/kg/day, which is 56 g/day for men and 46 g/day for women. Same Health Canada table [2] |
| AMDR (acceptable macronutrient distribution range) | A range of calories from protein, developed to express recommendations within a complete diet [1] | Adults 19 and over: 10 to 35 percent of energy. Same Health Canada table [2] |
| AR and PRI (European Union) | Average requirement and population reference intake | Healthy adults, EFSA 2012 as quoted by the European Commission: AR 0.66 and PRI 0.83 g/kg/day [3] |
Health Canada's gram-per-day figures are the per-kilogram amount multiplied by a reference weight. [2] For separate figures for children, pregnancy and other countries, see Protein Intake Levels and RDA, AI, DV and UL.
Nitrogen balance: the method behind the RDA
Nitrogen balance is the foundation of the current EAR and RDA for adults. [4] Researchers feed volunteers set amounts of protein and look for the lowest intake at which the body stops losing nitrogen. [1] The method needs strict diets for weeks and repeated 24-hour urine and stool collections, which is hard to do, especially with older adults. [4]The US and Canadian values come from a pooled analysis of 235 people in 19 studies. [5] Only one of those studies involved older adults. [4] A 2025 review pooled 395 people and again found no differences by sex, age group, climate or protein source, but results varied widely between studies, which the authors say limits firm conclusions. [6]
Wolfe and colleagues describe the RDA as derived to estimate the minimum protein needed to avoid a loss of body nitrogen, and note that the lowest end of the AMDR is higher than the RDA. [1] One author disclosed grants or fees from beef and beverage companies, and the meeting behind the paper was funded by beef, dairy and egg organizations. [1]
Indicator amino acid oxidation (IAAO)
IAAO is a short, less invasive method. Its logic is that amino acids are either built into protein or burned for energy. [4] Volunteers eat different protein amounts while researchers track how quickly a marker amino acid is oxidized; the point where oxidation stops falling is taken as the requirement. [4]| Study | Population and method | Result |
|---|---|---|
| Health Canada table (2005 values) | Adults 19 and over; the EAR and RDA rest on nitrogen balance [4] | EAR 0.66, RDA 0.80 g/kg/day [2] |
| Elango and colleagues, 2010 review | Adult men, IAAO | Mean 0.93 and population-safe 1.2 g/kg/day [7] |
| Same review | Nitrogen balance data reanalyzed with two-phase regression | Mean 0.91 and safe 0.99 g/kg/day [7] |
| Tang and colleagues, 2014 | Six women aged 80 to 87, IAAO | Mean 0.85 g/kg/day (95% CI 0.60 to 1.09); the interval includes the current EAR [4] |
| Tagawa and colleagues, 2025 meta-analysis | Nonathletes, IAAO versus nitrogen balance | 0.88 versus 0.64 g/kg/day, about 36 percent higher with IAAO [8] |
Cautions: the octogenarian study had six participants, and its authors state uncertainty about whether IAAO is valid for this purpose. [4] Both methods are short-term estimates, so higher values need confirming by longer studies of body composition, function and health outcomes. [4] The reanalyzed nitrogen balance figure is not the accepted value in the US and Canadian tables. [4] Some authors of the 2025 meta-analysis are employed by a food company. [8]
Where the debate stands
- For raising the figure: Elango and colleagues called for an urgent reassessment of adult recommendations. [7] Traylor and colleagues propose that older people consume at least 1.2 g/kg/day, while saying they need more long-term trials. [9] They also state that kidney and bone concerns about higher intakes lack a scientific foundation in humans. [9] That is one perspective paper's view, and people with kidney disease need individual advice (see below).
- For caution: EFSA, as quoted by the Commission, found the data insufficient to set a separate requirement for older adults. [3] A nitrogen balance study cited by Tang's group found no difference between young and older adults. [4]
- Other national guidance, as quoted: Germany's DGE gives an estimated value of 1.0 g/kg/day for people over 65, and the Nordic recommendations 2023 give 1.2 to 1.5 g/kg/day for older adults. [3] The US Dietary Guidelines 2025 to 2030 list "protein serving goals" of 1.2 to 1.6 g/kg/day, adjusted for calorie needs. [10] The text we extracted does not state the age groups or the evidence behind that range, and it differs from the 0.80 g/kg/day RDA in the Health Canada table of the 2005 US and Canadian values. [2]
- Upper end: WHO/FAO/UNU (2007), as quoted, set a 0.83 g/kg/day safe level for healthy adults, expected to meet the needs of 97.5 percent, and said no safe upper limit has been identified. [3]
For older adults and muscle, see Protein and Sarcopenia. For why studies reach different answers, see Why Protein and Amino Acid Trials Disagree.
Frequently asked questions
Why do some bodies say 0.8 and others 0.83 g/kg/day?
The US and Canadian RDA for adults is 0.80 g/kg/day, while EFSA's population reference intake is 0.83 g/kg/day. [2][3] Each body uses its own analysis; the sources we read do not explain the gap further.
Is the RDA the amount that gives the best health?
Not necessarily. Wolfe and colleagues describe it as derived to estimate the minimum needed to avoid nitrogen loss. [1] Whether more brings health benefits, particularly in older age, is still debated. [9]
What is nitrogen balance in plain words?
It compares the nitrogen going in with protein to the nitrogen leaving the body. The RDA is built on the lowest intake that reaches zero balance. [1]
Does IAAO prove we need more protein?
No. The studies are small and short, the authors of one say the findings must be confirmed by longer studies of health outcomes, and they state uncertainty about the method's validity. [4]
Is there an upper limit for protein?
The Health Canada table shows "ND" (not determined) in the upper limit column for adults. [2] WHO/FAO/UNU, as quoted, said no safe upper limit has been identified. [3] People with kidney disease need individual advice from their care team. [11]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety and who should ask a clinician
References
- Wolfe RR, Cifelli AM, Kostas G, Kim IY. Optimizing protein intake in adults: interpretation and application of the Recommended Dietary Allowance compared with the Acceptable Macronutrient Distribution Range. Advances in Nutrition 2017;8(2):266-275. Read 2026-10-23.
- Health Canada: Dietary reference intakes tables, reference values for macronutrients (2005 values from the US and Canadian Dietary Reference Intakes; page dated 2025-11-19). Read 2026-10-23 through a web-fetch tool, because direct download from this network failed.
- European Commission Knowledge4Policy: Dietary recommendations for protein intake for adults and older adults (quotes EFSA 2012, WHO/FAO/UNU 2007, DGE 2019, NNR 2023 and ANSES), last updated 31 March 2026. Read 2026-10-23. The EFSA original (efsa.onlinelibrary.wiley.com) returned HTTP 403, so the EFSA and WHO figures are as quoted by the Commission.
- Tang M, McCabe GP, Elango R, Pencharz PB, Ball RO, Campbell WW. Assessment of protein requirement in octogenarian women with use of the indicator amino acid oxidation technique. American Journal of Clinical Nutrition 2014;99(4):891-898. Read 2026-10-23.
- Rand WM, Pellett PL, Young VR. Meta-analysis of nitrogen balance studies for estimating protein requirements in healthy adults. American Journal of Clinical Nutrition 2003;77(1):109-127 (PubMed abstract). Read 2026-10-23.
- Suzuki D, et al. Nitrogen requirements in healthy adults: a systematic review and meta-analysis of nitrogen balance studies. Nutrients 2025;17(16):2615. Read 2026-10-23.
- Elango R, Humayun MA, Ball RO, Pencharz PB. Evidence that protein requirements have been significantly underestimated. Current Opinion in Clinical Nutrition and Metabolic Care 2010;13(1):52-57 (PubMed abstract). Read 2026-10-23.
- Tagawa R, et al. Comparison of protein requirements based on the nitrogen balance and indicator amino acid oxidation methods: an umbrella review and meta-analysis. Journal of Nutrition 2025;155(11):3877-3885 (PubMed abstract). Read 2026-10-23.
- Traylor DA, Gorissen SHM, Phillips SM. Perspective: protein requirements and optimal intakes in aging: are we ready to recommend more than the Recommended Dietary Allowance? Advances in Nutrition 2018;9(3):171-182 (PubMed abstract). Read 2026-10-23.
- U.S. Department of Health and Human Services and U.S. Department of Agriculture: Dietary Guidelines for Americans, 2025-2030 (PDF from realfood.gov; read as extracted text). Read 2026-10-23.
- NIDDK (U.S. National Institutes of Health): Eating and nutrition for chronic kidney disease, last reviewed January 2025. Read 2026-10-23.