Protein, explained through food.
A readable guide to combining foods, protein quality and what the evidence can — and cannot — tell us. The source cutoff is October 24, 2026. This is an ongoing scoped review, not an exhaustive systematic review.
Protein amount and amino-acid balance answer different questions
A food can supply a useful amount of protein while having relatively little of one indispensable amino acid. A different food can supply more of that amino acid. Compare the combined quantities with a stated reference pattern; do not mark an entire plant-food category “incomplete.” The selected USDA black-bean record, for example, meets the adult composition pattern before rice is added. This is a composition observation, not a digestibility result. Reproducible examples
Use total protein to answer “how much protein is in this meal?” Use the amino-acid profile to explain balance. An optional reference-equivalent amount summarizes that balance; it is capped at total protein, excludes unknown digestion effects, and does not split food into usable and wasted piles. The pattern describes amounts per gram of protein, not a person's daily amino-acid requirement. Methods and equations
Combining foods can help, but the recipe matters
Complementarity depends on the proportions and the actual food records. Two foods limited by the same amino acid may offer little improvement. The rice-and-bean example changes as the ratio changes, while a hemp/pumpkin-seed pair remains lysine-limited. A small portion also cannot meet a large protein goal simply because its ratios look balanced. Composition examples
Experimental evidence is comparison-specific too. In the cooked pulse/cereal pig experiment, mixtures improved on the grains but scored below the pulses. Those experimental ingredients were prepared and incorporated into test diets; their proportions cannot automatically become cooked kitchen serving weights. The study also reuses earlier pulse measurements, so it is not independent replication of every component. Pulse/cereal experiment
Human indicator-amino-acid-oxidation studies of rice/pulses and millet/lentils were located through citation tracing. Full primary-text access remains unresolved for several of them. They are discovery leads, not a source of coefficients for the calculator. Citation and access records
A varied day matters, and timing is a separate question
The body handles amino acids through ongoing turnover; it does not require every ingredient to match a reference pattern on its own. A review of vegetarian diets explains how varied diets can provide sufficient protein and amino acids, while noting limitations for restrictive patterns and particular populations. Its timing discussion includes mechanistic and animal evidence, so it cannot establish that every meal schedule is equivalent. Vegetarian-diet review
The daily tool can combine recorded amino-acid amounts and assess the day's composition. It cannot infer the same muscle response from different meal distributions. Exercise guidance discusses distribution and per-meal amounts in a different context from ordinary protein adequacy. Avoid a mandatory same-mouthful rule, an unlimited amino-acid-storage claim, or a promise that timing never matters. ISSN exercise position
A protein-quality score is not a percentage absorbed
Composition scores compare amino-acid proportions. PDCAAS additionally uses a fecal protein-digestibility measure and its own method conventions. DIAAS uses amino-acid-specific ileal digestibility. Neither is a general food-health score. The reference age, exact preparation, method and evidence species must accompany comparisons. FAO protein-quality report
Human tracer methods offer valuable evidence but may measure a limited panel and depend on calibration and first-pass-metabolism assumptions. The human legume papers do not provide all the groups required for a complete calculator DIAAS. Do not fill gaps with another species, an average food-group percentage or a scalar published score. Human tracer method, human legume study
The published fried-egg benchmark reproduces numerically. A separate pulse paper's printed inputs do not reconcile with its reported score table, so quantitative reuse is withheld. This is why source checking is necessary even after locating a published number. Benchmark and discrepancy records
Cooking and preparation belong in the food's identity
Use separate records for raw, boiled, roasted, drained, dehulled, fermented or otherwise prepared foods. Water changes edible-weight concentration; analytical composition and digestibility can also change. Do not convert a raw amino-acid table into a cooked one with a generic “cooking factor.”
In a human mung-bean study, dehulling increased the reported seven-amino-acid mean from 63.2% to 70.9%, a difference of 7.7 percentage points. Effects differed by amino acid and the panel was incomplete for nine-group scoring. It does not supply a universal dehulling bonus. Human legume study, Tables 4–5
A Russet-potato study illustrates another tradeoff: cooking improved rat fecal protein digestibility, while frying reduced the amino-acid score. Its child-pattern PDCAAS cannot be ranked directly against adult DIAAS. Soaking, germination and fermentation findings likewise need an exact food/preparation match before numerical use; no generic adjustments are approved. Potato experiment
Adding to eggs or meat can improve a meal without improving its protein score
The egg-breakfast pig study found that adding eggs improved the tested bread/potato meals. The mixtures scored below eggs alone. Predictions were not statistically different from measured mixture DIAAS in those recipes, but some individual amino-acid predictions differed; this does not prove universal additivity. The work was funded by the Egg Nutrition Center. Egg-breakfast experiment
The USDA examples show why “enhancement” needs a named outcome. Egg/potato/spinach and chicken/lentil/broccoli mixtures add fiber at equal protein while changing calories and lowering the uncapped composition score. They still meet the selected pattern. Compare animal and plant foods at equal protein, with a separate equal-calorie view; do not invent equivalent egg counts from incompatible quality measures. Practical comparisons
A human trial comparing food-group ounce equivalents found different acute protein responses, but its portions supplied different protein amounts. It is not an equal-protein comparison. The study's meat/egg funding and author disclosures remain part of its appraisal. Ounce-equivalent trial
Meal interactions can make digestion less predictable
Five adults had lower measured egg amino-acid digestibility with a strong tea preparation than in their earlier no-tea measurements. The control was historical, the sample was small, and the seven-amino-acid panel did not establish a full DIAAS. This is evidence to examine meal interactions, not a universal penalty for tea. Egg and tea study
No digestion adjustment is currently approved for a catalog food. The first supported calculations therefore concern composition, while the research library can explain measured protein quality in specific studies. Any later ingredient-based digestible estimate must meet the complete-input and preparation-compatibility requirements and remain labelled as a modelled mixture.
Muscle studies do not validate a “complete-protein grams” promise
In 45 trained young men, boiled eggs produced higher amino-acid peaks than raw eggs, but the trial did not detect a between-group difference in five-hour muscle protein synthesis. A separate ten-day trial in 27 middle-to-older adults found an exercise effect without a detected difference between supplemented plant-focused and animal-focused diets. These are different endpoints from food composition; short trials and nonsignificant findings do not prove universal equivalence. Egg recovery trial, diet and training trial
Likewise, the leucine-trigger review found that support varied by population and whether proteins were isolated or supplied as whole foods. Show leucine amounts, but do not promise muscle gain after a fixed threshold is crossed. Leucine review
Vegan diets are not all alike
Three-day records from German vegans generally exceeded the study's average-requirement thresholds, whereas a Danish sample more often fell below its references. These surveys differ in participants, databases and intake methods; short records do not establish long-term deficiency. The Danish authors published a correction distinguishing average requirements from recommended intakes. Its 60% protein result concerns the WHO average requirement; 50% met the separate Nordic recommendation on all three days. German study, Danish study, correction
A five-day study in 18 minimally active vegan men found negative nitrogen balance at 0.8 g/kg/day. It used estimated non-urea losses, one protein dose, a short adaptation period and a menu including formulated products. It raises an adequacy question but cannot establish a new universal vegan requirement or a multiplier for every plant food. Nitrogen-balance study
More than one protein goal is legitimate to display
Keep distinct choices for the U.S./Canadian adult RDA, EFSA adult reference intake, current U.S. dietary-guideline range, and source-specific exercise guidance. Explain the population and purpose of each. Do not relabel a guideline goal as an RDA, collapse a range to a midpoint without selection, or silently change micronutrient references when a protein goal changes. Goal catalog with primary citations
The first supported personal references concern healthy adults aged 19 and older, outside pregnancy/lactation. Clinical conditions, children and special life stages need separate assessment. An age-dependent result for one food cannot justify a percentage reduction for all foods in older people. Young/older adult tracer comparison
Micronutrient content is useful, but it is not absorbed intake
Show calories, macronutrients and available vitamins/minerals alongside protein. Iron and zinc absorption depend on factors including nutrient form, food matrix and meal context. Vitamin C can improve nonheme iron absorption, while phytate can reduce zinc availability. This does not justify computing exact absorbed minerals from a generic ingredient list. NIH iron reference, NIH zinc reference
Daily comparisons must distinguish RDA, AI, DV, UL and sodium's CDRR. Preserve nutrient forms and limits restricted to supplements or fortification. Unknown iodine or another missing value remains unknown, and an incomplete nutrient total does not earn an exact percentage. Total sugar is not automatically added sugar. Daily-reference specification
Practical measurements and exclusions are part of accuracy
Tablespoons describe volume, not a universal mass. Use food-specific anchors, explicit U.S./metric conventions, and canonical grams that survive unit changes. Chia's cup-derived spoon estimate and the user's original quantities are documented separately from a suggested serving. A smoothie's final volume requires measurement. Household-measure audit
Traditional foods require exact variants. Tofu, tempeh, yogurt, cheese and bread can differ in ingredients, preparation and nutrient coverage. Keep soy/dairy/wheat and other exclusions inherited through defined ingredients; unknown formulations cannot pass a strict exclusion check. Generic nutrition records do not establish absence of manufacturing cross-contact. The natural-peanut-butter alternative has a coherent but source-imputed profile; its full formulation remains unknown. Catalog decisions
What remains unknown
The discovery index is much larger than the appraised subset. Some primary articles and correction notices remain inaccessible; some composition records lack amino acids or household measures. Food and preparation matches for digestibility are not approved. These gaps are disclosed rather than filled with invented values. The reference should grow as sources are checked, without representing an unfinished review as exhaustive or independently reviewed. Research readiness, checkpoints
What changes when foods come together?
These database examples all supply 20 g of protein. They are scaled comparisons, not serving recommendations. Scores concern composition; digestion is not compared.
| Food or combination | Food weight | Energy | Fiber | Balance score |
|---|---|---|---|---|
| White rice | 743 g | 967 kcal | 3.0 g | 75.1 |
| Black beans | 226 g | 298 kcal | 19.6 g | 112.4 |
| White rice + Black beans | 346 g | 454 kcal | 15.8 g | 127.2 |
| White rice + Black beans | 560 g | 730 kcal | 8.9 g | 99.2 |
| Whole egg | 159 g | 246 kcal | 0.0 g | 140.1 |
| Whole egg + Potato + Spinach | 338 g | 345 kcal | 5.0 g | 126.0 |
| Chicken breast | 64 g | 106 kcal | 0.0 g | 123.0 |
| Chicken breast + Lentils + Broccoli | 173 g | 167 kcal | 7.5 g | 120.1 |
| Rolled oats + Chia seeds + Plain whole-milk yogurt | 330 g | 481 kcal | 13.5 g | 141.9 |
| Hemp seeds + Pumpkin seed kernels | 65 g | 360 kcal | 3.2 g | 84.7 |
A larger score is not a universal health ranking. A well-balanced protein food may gain fiber or minerals from a combination while its composition score goes down.
Inside the research.
Twenty-four appraised source records, with everyday titles and original citations. Human, animal and review evidence answer different questions.
24 source records
Beans can improve a grain's protein balance without making the mixture complete
In a pig study, two cooked bean-and-grain mixtures scored above their grains alone but below their beans alone. Both mixtures still had a limiting amino acid.
What was tested & what it means
Who or what was studied
Seven growing pigs; six observations per dietary treatment in an incomplete Latin square.
How it was measured
True ileal amino-acid digestibility; FAO older-child/adolescent/adult pattern.
Food and preparation
Named varieties, soaked, steam-cooked, hot-air dried and ground before incorporation into experimental diets; mixtures are not cooked kitchen serving weights.
What this supports
Method and comparison evidence; no coefficient join to current USDA pilot records.
Funding and disclosures
Public institute basic-research funds and a Ministry of Finance grain-industry database/service project; authors declared no conflicts.
Original citation
Han F, Moughan PJ, Li J, Stroebinger N, Pang S. The Complementarity of Amino Acids in Cooked Pulse/Cereal Blends and Effects on DIAAS. 2021-09-24. DOI: 10.3390/plants10101999
Cooked beans do not all have the same protein quality
Six cooked pulses had different amino-acid digestibility and limiting amino acids in growing pigs. A single digestibility percentage for all beans would hide these differences.
What was tested & what it means
Who or what was studied
Seven cannulated growing pigs; seven diets across six periods.
How it was measured
True ileal amino-acid digestibility with a nitrogen-free diet for endogenous losses.
Food and preparation
Named Chinese varieties; soaked 12 h, steam-cooked 70 min, then hot-air dried and milled for experimental diets. Not edible cooked serving weights.
What this supports
Methods context only pending analytical-basis reconciliation; reported DIAAS values must not be used as validated calculator inputs or directly ranked against other foods.
Funding and disclosures
Public research funding; authors declared no conflicts.
Original citation
Han F, Moughan PJ, Li J, Pang S. Digestible Indispensable Amino Acid Scores (DIAAS) of Six Cooked Chinese Pulses. 2020-12-15. DOI: 10.3390/nu12123831
Eggs improved the tested breakfasts, but the mixtures scored below eggs alone
A pig experiment found that adding eggs improved bread or potato meals. The mixtures did not improve on eggs' own amino-acid score. Agreement with predicted mixture scores was limited to the tested recipes.
What was tested & what it means
Who or what was studied
Nine cannulated female pigs; nine-by-six Youden square plus a nitrogen-free period.
How it was measured
Standardized ileal digestibility and age-specific DIAAS.
What this supports
Method validation and contextual benchmarks only; experimental commercial foods do not establish eligibility for the product catalog.
Important limits
No statistically detected DIAAS difference is not proof of exact equality. Some amino-acid-specific predictions differed.
Funding and disclosures
Egg Nutrition Center funded the work; authors declared no conflicts.
Original citation
Fanelli NS, Martins JCFR, Stein HH. The digestible indispensable amino acid score (DIAAS) in eggs and egg-containing breakfast meals is greater than in toast breads or hash browns served without eggs. 2024-11-12. DOI: 10.1017/jns.2024.71
Human digestion measurements depend on the food and the measurement method
A small human tracer experiment studied chickpea and mung-bean meals and a dehulled variant. Its measurements cannot supply every amino-acid coefficient needed for a complete meal score.
What was tested & what it means
Who or what was studied
Six healthy adults, three men and three women, aged 18–45; study conducted in Bangalore. Per-protocol sample details remain to be checked before pooled inference.
How it was measured
Dual stable-isotope approach, calibrated spirulina reference, plateau-fed mixed meals.
What this supports
Relevant human-method evidence; recipe preparation and incomplete amino-acid panel prevent a direct full-profile join.
Important limits
Do not confuse the table's average over its reported analytes with a complete nine-group DIAAS or combine these coefficients with unrelated pig values.
Funding and disclosures
Wellcome Trust/DBT India Alliance fellowship; authors reported no conflicts.
Original citation
Devi S, Varkey A, Sheshshayee MS, Preston T, Kurpad AV. Measurement of protein digestibility in humans by a dual-tracer method. 2018-06-01. DOI: 10.1093/ajcn/nqy062
Age differences in digestion were not the same for every food
A 2026 human study found a lower tracer ratio for two amino acids from sorghum in older adults. It did not detect the same age difference for milk or black beans.
What was tested & what it means
Who or what was studied
Ten young and ten older adults; randomized crossover, three protein sources.
How it was measured
Dual-tracer plasma-to-meal ratios, focusing on lysine and threonine.
What this supports
Population/method limitation; not a complete set of absolute digestibility coefficients.
Important limits
Do not reduce every food's protein or digestibility by 19% for older users.
Funding and disclosures
Public–private funding included dairy companies; one author disclosed industry employment.
Original citation
Hinssen F, Tessier R, van Harskamp D, Huppertz T, Mensink M, van der Wielen N. Differences in amino acid digestibility between young and older adults: a randomized crossover study using the dual tracer method. 2026-05-19. DOI: 10.1016/j.ajcnut.2026.101361
Almonds contain protein, but lysine limits their balance
An almond study found lysine to be the limiting amino acid across the tested varieties. It used fecal digestibility and PDCAAS, which cannot be treated as an ileal DIAAS measurement.
What was tested & what it means
Who or what was studied
Four composite almond varieties from the 2017 California harvest and historical composition analyses; detailed rat sample size is not supplied in the inspected methods subsection, which refers to previous protocols.
How it was measured
True fecal protein digestibility by modified AOAC 991.29 rat method; in-vitro pH drop in duplicate; PDCAAS uses the 2–5-year-old child pattern, not the FAO adult pattern.
What this supports
Supports method-specific limits and varietal comparison, not per-amino-acid ileal coefficients.
Important limits
Child-pattern PDCAAS is not directly comparable with adult DIAAS. Historical analyses have varying sample sizes and reported outlier exclusions.
Funding and disclosures
Almond Board of California supplied funding, samples, and historical data; authors declared no conflicts.
Original citation
House JD, Hill K, Neufeld J, Franczyk A, Nosworthy MG. Determination of the protein quality of almonds (<i>Prunus dulcis</i> L.) as assessed by in vitro and in vivo methodologies. 2019-07-29. DOI: 10.1002/fsn3.1146
One short vegan study raises a question about the protein RDA
Eighteen minimally active vegan men had negative nitrogen balance after five days at 0.8 grams of protein per kilogram. The study raises an adequacy question but does not establish a new requirement.
What was tested & what it means
Who or what was studied
18 minimally active men; single intake level, five-day supplied diet, no concurrent omnivore control.
How it was measured
Day-five urinary urea nitrogen; other losses estimated with a fixed 4 g/day allowance.
What this supports
Counterevidence to unconditional adequacy claims. Do not enable an automatic vegan multiplier or treat the authors’ calculated higher dose as a tested requirement.
Important limits
Short adaptation, self-reported adherence, estimated non-urea losses, and one tested dose limit inference. The example menu includes commercial meals and a protein shake; it is not a whole-food menu trial.
Funding and disclosures
No external funding or conflicts declared.
Original citation
Bartholomae E, Johnston CS. Nitrogen Balance at the Recommended Dietary Allowance for Protein in Minimally Active Male Vegans. 2023-07-16. DOI: 10.3390/nu15143159
Some vegan food records fell short on protein and amino acids
In three-day records from 40 Danish vegans, some participants fell below the study’s intake references. Lysine was a frequent gap. Short food records cannot establish an individual’s long-term deficiency.
What was tested & what it means
Who or what was studied
40 Danish vegans; three-day weighed records; self-reported body weight and activity.
How it was measured
Database composition compared with WHO average requirements (protein 0.66 g/kg/day) and a separate Nordic recommended protein intake of 0.8 g/kg/day, as clarified by the 2024 correction.
What this supports
Supports day-level accounting and explaining missing intake context. Different thresholds must be retained when comparing other surveys.
Important limits
Self-selection, short records, database uncertainty and self-report limit generalization. Reference comparisons are not clinical diagnoses.
Funding and disclosures
Danish public programme GUDP funding; no competing interests declared.
Original citation
Aaslyng MD, Dam AB, Petersen IL, Christoffersen T. Protein content and amino acid composition in the diet of Danish vegans: a cross-sectional study. 2023-11-15. DOI: 10.1186/s40795-023-00793-y
Another vegan survey found mostly sufficient amino-acid intake
A German study of 36 vegans and 36 omnivores found lower amino-acid intakes in vegans, but only one vegan fell below its average-requirement threshold for protein and lysine.
What was tested & what it means
Who or what was studied
36 vegans and 36 omnivores aged 30–60; three-day weighed food records and laboratory measurements.
How it was measured
Dietary intake and plasma amino acids; WHO estimated average requirement comparison.
What this supports
Counterbalance to universal inadequacy claims. Plasma concentration is not a direct measure of dietary adequacy or food digestibility.
Important limits
A short record is not usual intake; some vegan foods lacked amino-acid data. EAR comparisons are separate from RDA thresholds; populations, databases and reporting methods differ between surveys.
Funding and disclosures
No competing interests declared; complete funding locator remains pending.
Original citation
Dietrich S, Trefflich I, Ueland PM, Menzel J, Penczynski KJ, Abraham K, Weikert C. Amino acid intake and plasma concentrations and their interplay with gut microbiota in vegans and omnivores in Germany. 2022-01-16. DOI: 10.1007/s00394-021-02790-y
Equal food-group servings did not provide equal protein responses
In 56 young adults, animal foods produced greater acute net protein balance than the tested plant foods at food-group ounce equivalents. Those portions contained different amounts of protein and essential amino acids.
What was tested & what it means
Who or what was studied
56 healthy young adults, eight per parallel group; seven single-food interventions.
How it was measured
Stable-isotope whole-body protein kinetics after two food-group ounce equivalents.
What this supports
Supports explicit equal-protein and equal-energy comparators, not an equal-protein superiority claim.
Important limits
Acute isolated-food comparison, neither equal protein nor equal energy. It cannot rank long-term outcomes or isolate protein source from dose.
Funding and disclosures
Pork, egg and beef organizations funded the work; an author disclosed related honoraria, travel and company shareholdings.
Original citation
Park S, Church DD, Schutzler SE, Azhar G, Kim IY, Ferrando AA, Wolfe RR. Metabolic Evaluation of the Dietary Guidelines' Ounce Equivalents of Protein Food Sources in Young Adults: A Randomized Controlled Trial. 2021-05-01. DOI: 10.1093/jn/nxaa401
Exercise improved muscle protein synthesis in both tested diets
A ten-day trial in 27 adults aged 50–70 found higher muscle protein synthesis in trained legs, without a detected difference between the tested plant-focused and animal-focused diets.
What was tested & what it means
Who or what was studied
27 adults aged 50–70; randomized parallel diet groups with unilateral resistance exercise.
How it was measured
Integrated myofibrillar protein synthesis; 1.0 g protein/kg/day, with pea or whey supplements.
What this supports
Outcome context only; isolates are not eligible catalog foods or whole-food coefficients.
Important limits
Short duration, small groups and supplemented diets; no detected difference is not proof of universal equivalence or long-term muscle gain.
Funding and disclosures
Joint university/Volac studentship; an industry employee participated in conceptualization and revisions, and other protein-industry relationships were disclosed.
Original citation
Korzepa M, Quinlan JI, Marshall RN, Rogers LM, Belfield AE, Elhassan YS, Lawson A, Ayre C, Senden JM, Goessens JP, Glover EI, Wallis GA, van Loon LJ, Breen L. Resistance training increases myofibrillar protein synthesis in middle-to-older aged adults consuming a typical diet with no influence of protein source: a randomized controlled trial. 2025-04-25. DOI: 10.1016/j.ajcnut.2025.04.019
Tested protein blends showed similar responses in older men
Thirty-two older men received one of four protein blends. The study did not detect differences in its relative digestion measure or muscle protein synthesis between blends.
What was tested & what it means
Who or what was studied
32 healthy men aged 65–75; eight per group; trickle-fed protein blends.
How it was measured
Dual-isotope relative dilution technique and muscle biopsies; total 20 g protein.
What this supports
Method/outcome context only. Formulated blends are outside the food catalog; relative tracer ratios are not absolute per-amino-acid coefficients.
Important limits
Small groups, trickle feeding and a method requiring further validation. The early biopsy followed about 11.8 g protein, not the full dose.
Funding and disclosures
Fresenius Kabi funded the investigator-initiated study; public infrastructure funding; authors declared no conflicts.
Original citation
Cox J, Phillips BE, Bunce J, Smart T, Wall J, Crossland H, Wilkinson DJ, Smith K, Atherton PJ. Investigating the Digestibility, Bioavailability and Utilization of Protein Blends in Older Adults Using a Dual Stable Isotope Tracer Technique. 2025-10-23. DOI: 10.3390/nu17213328
A varied day matters more than a perfect score for every food
This review explains how varied vegetarian diets can meet protein and amino-acid needs. It also identifies uncertainty for restrictive diets and people with higher needs.
What was tested & what it means
Who or what was studied
Published adult dietary surveys and experimental studies; specific-population discussion.
How it was measured
Narrative synthesis, not a new digestion or outcome experiment.
What this supports
Support day-level context while retaining meal-level quantities. Do not claim indefinite storage of amino acids or that timing never matters.
Important limits
Timing arguments include mechanistic and animal evidence. The review predates later counterevidence; it does not prove that all meal schedules or vegan diets are equivalent.
Funding and disclosures
No external funding for the review; one author disclosed leadership of a plant-protein industry research contract without personal fee.
Original citation
Mariotti F, Gardner CD. Dietary Protein and Amino Acids in Vegetarian Diets-A Review. 2019-11-04. DOI: 10.3390/nu11112661
Exercise guidance uses a different protein goal from the adult RDA
The 2017 ISSN position gives 1.4–2.0 grams per kilogram per day for most healthy exercising people. This is sports guidance, not a replacement for the general adult RDA.
What was tested & what it means
Who or what was studied
Healthy exercising individuals; separate discussion of energy restriction and older adults.
How it was measured
Society position based on a literature review.
What this supports
Eligible as a clearly labelled optional exercise goal, separate from the joint 2016 athletic range of 1.2–2.0.
Important limits
Context-specific range; special high-dose scenarios are not a universal default. Verify updates before launch.
Funding and disclosures
No funding for the statement; multiple authors disclosed supplement-industry research, advisory, employment or commercial relationships.
Original citation
Jäger R, Kerksick CM, Campbell BI, Cribb PJ, Wells SD, Skwiat TM, Purpura M, Ziegenfuss TN, Ferrando AA, Arent SM, Smith-Ryan AE, Stout JR, Arciero PJ, Ormsbee MJ, Taylor LW, Wilborn CD, Kalman DS, Kreider RB, Willoughby DS, Hoffman JR, Krzykowski JL, Antonio J. International Society of Sports Nutrition Position Stand: protein and exercise. 2017-06-20. DOI: 10.1186/s12970-017-0177-8
A correction clarifies which intake threshold the vegan study used
The authors corrected their use of “recommended intake” and “average requirement.” The study’s 60% protein result concerns the WHO average requirement; 50% met the separate Nordic recommendation on all three days.
What was tested & what it means
Who or what was studied
Correction to PMID 37968717; not an additional experiment.
How it was measured
Author correction of terminology and related result descriptions.
What this supports
Always link and apply when summarizing the original study; do not count as independent evidence.
Original citation
Aaslyng MD, Dam AB, Petersen IL, Christoffersen T. Correction: Protein content and amino acid composition in the diet of Danish vegans: a cross-sectional study. 2024-04-16. DOI: 10.1186/s40795-024-00866-6
A drink alongside a meal can change digestion measurements
In five adults, strong black tea reduced measured egg amino-acid digestibility compared with an earlier egg meal. The small study shows why a meal’s digestion cannot always be predicted from separate ingredients.
What was tested & what it means
Who or what was studied
Five healthy Indian adults aged 20–27; earlier no-tea measurements in the same people; three also tested the reference protein.
How it was measured
Dual-isotope tracer technique; seven amino acids measured; plateau-fed egg, ghee rice and tomato curry.
Food and preparation
Tea prepared with 15 g leaves/powder in 240 g boiling water for 10 minutes; do not assume this represents every tea serving.
What this supports
Evidence against universal mixture additivity; do not apply a blanket tea penalty or create full meal DIAAS from these results.
Important limits
No randomized concurrent control; previous measurements were two months earlier. The method has calibration/first-pass assumptions and an incomplete nine-group panel.
Funding and disclosures
Wellcome Trust/DBT fellowship; no conflicts declared.
Original citation
Kashyap S, Shivakumar N, Varkey A, Preston T, Devi S, Kurpad AV. Co-ingestion of Black Tea Reduces the Indispensable Amino Acid Digestibility of Hens' Egg in Indian Adults. 2019-08-01. DOI: 10.1093/jn/nxz091
Removing the hull improved measured mung-bean digestion
A human tracer study found higher average amino-acid digestibility for dehulled mung beans than whole mung beans. Effects differed by amino acid, so one preparation factor cannot describe every nutrient.
What was tested & what it means
Who or what was studied
Healthy Indian adults; six participants per main legume group; five in the alternate-reference validation.
How it was measured
Dual-isotope tracer method with a calibrated spirulina reference; seven-amino-acid panel.
What this supports
Use separate preparation records; no automatic dehulling multiplier for arbitrary foods or nutrients.
Important limits
Panel means are not complete nine-group scores. Free-amino-acid absorption and similar first-pass metabolism are assumptions; prior reference-protein calibration used different people.
Funding and disclosures
Wellcome Trust/DBT and IAEA support; no conflicts declared.
Original citation
Kashyap S, Varkey A, Shivakumar N, Devi S, Reddy B H R, Thomas T, Preston T, Sreeman S, Kurpad AV. True ileal digestibility of legumes determined by dual-isotope tracer method in Indian adults. 2019-10-01. DOI: 10.1093/ajcn/nqz159
Cooking changed potato protein quality in different ways
In a Russet-potato experiment, cooking improved fecal protein digestibility in rats, while frying reduced the amino-acid score. Better digestion alone did not guarantee the highest overall score.
What was tested & what it means
Who or what was studied
Study-specific Russet potatoes; rat assay and several laboratory digestion methods.
How it was measured
True fecal protein digestibility and PDCAAS using a 2–5-year-old child pattern; not adult DIAAS.
What this supports
Preserve cooking variants and method labels. Do not rank child-pattern PDCAAS against adult DIAAS.
Important limits
Table 2 values retained rather than rounded abstract descriptions; assay/preparation-specific results cannot be transferred to all potato varieties or human ileal coefficients.
Funding and disclosures
Alliance for Potato Research and Education funding and donated potatoes; authors declared no conflicts.
Original citation
Bailey T, Franczyk AJ, Goldberg EM, House JD. Impact of cooking on the protein quality of Russet potatoes. 2023-10-03. DOI: 10.1002/fsn3.3734
Higher amino-acid peaks did not produce a detected muscle-synthesis difference
Boiled eggs produced higher peak blood amino acids than raw eggs in 45 trained young men. The trial did not detect a difference between groups in muscle protein synthesis over five hours.
What was tested & what it means
Who or what was studied
45 healthy resistance-trained young men, 15 per group; randomized parallel trial after resistance exercise.
How it was measured
Five raw eggs, five boiled eggs or a lower-protein breakfast; stable-isotope myofibrillar protein synthesis.
What this supports
Do not turn amino-acid balance or blood amino-acid peaks into a muscle-gain prediction.
Important limits
The numerical increases relative to control were not statistically significant between groups. This acute endpoint does not establish identical digestion, long-term outcomes or a reason to prefer raw eggs.
Funding and disclosures
University internal funding; authors disclosed other nutrition-industry research relationships.
Original citation
Fuchs CJ, Hermans WJ, Smeets JS, Senden JM, van Kranenburg J, Gorissen SH, Burd NA, Verdijk LB, van Loon LJ. Raw Eggs To Support Postexercise Recovery in Healthy Young Men: Did Rocky Get It Right or Wrong? 2022-08-09. DOI: 10.1093/jn/nxac174
Leucine alone does not explain every muscle response
A review of 29 studies found more support for a leucine-trigger explanation in older adults and isolated-protein studies than in whole-food studies. A single leucine threshold is an incomplete model.
What was tested & what it means
Who or what was studied
29 eligible studies in young/older adults, at rest or after exercise.
How it was measured
Qualitative classification of blood leucine and muscle protein synthesis responses.
What this supports
Show leucine content as composition; do not label a meal as guaranteed muscle-building after crossing a threshold.
Important limits
Qualitative synthesis of unlike experiments, not a universal dose-response equation. Whole-food matrix and population matter.
Funding and disclosures
No commercial or financial conflicts declared; complete funding review remains open.
Original citation
Zaromskyte G, Prokopidis K, Ioannidis T, Tipton KD, Witard OC. Evaluating the Leucine Trigger Hypothesis to Explain the Post-prandial Regulation of Muscle Protein Synthesis in Young and Older Adults: A Systematic Review. 2021-07-08. DOI: 10.3389/fnut.2021.685165
Protein-quality scores answer a narrower question than overall food quality
This methods review describes progress in DIAAS measurement and unresolved questions about reference patterns, processing and human measurements. It supports keeping protein quality separate from overall health effects.
What was tested & what it means
Who or what was studied
Human and animal digestion-method literature; no new feeding trial.
How it was measured
Review of DIAAS ten years after the FAO consultation.
What this supports
Maintain separate composition, digestibility and broader-nutrition displays; do not convert a scalar score into ingredient coefficients.
Important limits
Methodological synthesis does not validate every food coefficient, mixed meal or population. Review conclusions need primary-data checks for numeric use.
Funding and disclosures
No commercial or financial conflicts declared.
Original citation
Moughan PJ, Lim WXJ. Digestible indispensable amino acid score (DIAAS): 10 years on. 2024-07-03. DOI: 10.3389/fnut.2024.1389719
Changing a few foods improved four modelled vegan menus
Researchers calculated protein quality for example menus; they did not feed the menus to people. Replacing some foods improved the estimates, but the result depends on borrowed digestion data and recipe assumptions.
What was tested & what it means
Who or what was studied
Four constructed daily menus for a hypothetical healthy Swiss man, age 30, 78 kg, moderate activity, 2500 kcal/day; no participants.
How it was measured
Modelled PDCAAS and DIAAS using composition and digestibility sources.
What this supports
Illustration of diet modelling and its limitations; no digestion coefficients approved.
Important limits
Table 1 screens foods using mixed reference ages and a PDCAAS substitution. Cooking ratios and borrowed coefficients are model assumptions; supplements not independently audited here. The abstract repeats day 1 LQ with contradictory quality labels; Table 7 identifies day 2 LQ as low. Do not copy this model as validated catalog data.
Funding and disclosures
No external funding; no conflicts declared.
Original citation
Rojas Conzuelo Z, Bez NS, Theobald S, Kopf-Bolanz KA. Protein Quality Changes of Vegan Day Menus with Different Plant Protein Source Compositions. 2022-03-04. DOI: 10.3390/nu14051088
One protein score cannot tell the whole story
This review separates amino-acid balance, digestion and the body’s response after eating. Preparation and population can change the interpretation; the review does not provide a universal correction for every food.
What was tested & what it means
Who or what was studied
Narrative review across food analyses, digestion methods and metabolic studies; no new participants.
How it was measured
Contextual synthesis of chemical scoring and stable-isotope methods.
What this supports
Research explanation and primary-study discovery; no automatic ingredient adjustments.
Important limits
Not a new controlled experiment. Figure 2 caption swaps the sulfur/aromatic group labels; use FAO definitions instead. Some examples use isolates or products outside the catalog.
Funding and disclosures
No funding for the review declared; several authors disclose dairy, beef, pork, supplement-related or other commercial relationships and patents. Full disclosures retained in original article.
Original citation
Matthews JJ, Arentson-Lantz EJ, Moughan PJ, Wolfe RR, Ferrando AA, Church DD. Understanding Dietary Protein Quality: Digestible Indispensable Amino Acid Scores and Beyond. 2025-07-15. DOI: 10.1016/j.tjnut.2025.07.005
Milk can change zinc absorption in some meals
A review describes studies where dairy helped zinc absorption from certain plant-based meals. The effect depended on the meal, so adding milk does not justify a fixed zinc-absorption bonus.
What was tested & what it means
Who or what was studied
Secondary review of meal absorption experiments; not a new trial.
How it was measured
Narrative synthesis of dairy, phytate and zinc absorption.
What this supports
Explain why nutrient content is not the same as absorbed intake. Primary follow-up remains in the access register.
Important limits
Relevant primary reports were identified but full-text appraisal remains unresolved. Do not turn secondary percentages into calculator coefficients or general dietary instructions.
Funding and disclosures
Dutch Dairy Association supported the review; authors declared no conflicts.
Original citation
Shkembi B, Huppertz T. Influence of Dairy Products on Bioavailability of Zinc from Other Food Products: A Review of Complementarity at a Meal Level. 2021-11-26. DOI: 10.3390/nu13124253
A reference that can keep growing.
Thirty-two discovery searches yielded 3,631 distinct records. Fifty-one studies were prioritized; 24 have structured extractions and 27 have unresolved primary-text access gaps. The remaining 3,580 discovery records have not been fully screened. Citation trails and correction checks inform the appraisal; this is not a completed systematic review or independent replication.
No exact food/preparation digestibility joins have been approved. We publish the calculator within that boundary and keep missing values visible. Download the public evidence records.