Evaluation of protein intake and protein quality in New Zealand vegans
Bi Xue Patricia SohiD, Matthieu VignesiD, Nick William SmithiD, Pamela R. von HurstiD, Warren Charles McNabbiD
Abstract
Dietary protein provides indispensable amino acids (IAAs) that the body cannot synthesise. Past assessments of total protein intake from vegan populations in western, developed countries were found to be low but not necessarily below daily requirements. However, plant-sourced proteins generally have lower quantities of digestible IAAs as compared to animal-sourced proteins. Simply accounting for protein intake without considering AA profile and digestibility could overestimate protein adequacy among vegans. This study quantified protein intake and quality, as compared to reference intake values among 193 NZ vegans using a four-day food diary. Protein and IAA composition of all foods were derived from New Zealand FoodFiles and the United States Department of Agriculture and adjusted for True Ileal Digestibility (TID). Mean protein intakes for males and females were 0.99 and 0.81 g/kg /day, respectively with 78.8% of males and 74.5% of females meeting the Estimated Average Requirement for protein. Plant-sourced proteins provided 52.9 mg of leucine and 35.7 mg of lysine per gram of protein and were below the reference scoring patterns (leucine: 59mg/g, lysine: 45mg/g). When adjusted to individual body weight, average IAA intakes were above daily requirements, but lysine just met requirements at 31.2 mg/kg of body weight/day (reference: 30 mg/kg/day). Upon TID adjustment, the percentage of vegans meeting adequacy for protein and IAA decreased and only approximately 50% of the cohort could meet lysine and leucine requirements. Hence, lysine and leucine were the most limiting IAAs in the vegan cohorts diet. Legumes and pulses contributed most to overall protein and lysine intake. An increased proportion of legumes and pulses can potentially increase these intakes but must be considered in the context of the whole diet. AA composition and digestibility are important aspects of protein quality when assessing protein adequacy and is of particular importance in restrictive diets.
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In-depth summary
Claude Opus 5.5 · xhigh effort · 8 Nov 2026 · from the full text of version 1 (22 Nov 2024) · CC BY 4.0
After true ileal digestibility adjustment, about half of 193 long-term New Zealand vegans fell short of lysine and leucine requirements, though most met the protein Estimated Average Requirement.
Vegan protein adequacy is usually judged on total protein, but plant proteins generally supply fewer digestible indispensable amino acids (IAAs) than animal proteins. The authors note that few earlier vegan studies assessed amino acid intake and none corrected it for digestibility; this work applies true ileal digestibility (TID) coefficients in what they describe as the first such analysis of long-term New Zealand vegans.
Key results
ShownLysine and leucine were the most limiting IAAs. Both fell below reference scoring patterns per gram of protein, and roughly half the cohort did not meet body-weight-based requirements for the digestible forms.
Leucine was 52.9 mg/g protein vs a 59 mg/g reference, and lysine 35.7 mg/g vs 45 mg/g. Mean lysine intake was 31.2 mg/kg/d vs a 30 mg/kg/d requirement. After TID adjustment, 56% of the cohort did not meet the digestible lysine requirement and 43.5% did not meet the leucine requirement. · Abstract; Impact of TID adjustment on protein and IAA…; Comparison of TID-adjusted IAA intake to…
ShownCorrecting for TID lowered estimated protein intake and reduced the share of vegans meeting requirements for protein and for every IAA, so estimates based on composition alone overstate adequacy.
Mean protein fell from 1.25 to 0.99 g/kg body weight/d in males and from 1.04 to 0.81 g/kg/d in females. The share meeting the protein EAR fell from 92.3% to 78.8% in males and from 90.8% to 74.5% in females. Adequacy dropped by at least 15% for lysine and for leucine. · Abstract; Impact of TID adjustment on protein and IAA…
ShownMeeting the total protein requirement did not guarantee IAA adequacy. Shortfalls in lysine and leucine persisted among people with enough protein, which was much less true for histidine.
Only 56.2% of those meeting the protein requirement were adequate for all digestibility-adjusted IAAs. Among people with adequate protein, 142 also met histidine needs vs 84 for lysine and 108 for leucine; 61 (lysine) and 37 (leucine) stayed below requirement despite adequate protein. · Comparison of TID-adjusted IAA intake to…; TID-adjust Protein and IAA intake relative to…; Figure legends
ShownLegumes and pulses supplied the largest share of protein and lysine. Grains and pasta supplied the most energy but less protein and lysine. Novel plant-based meat and dairy alternatives, built mainly on soy and pea protein, supplied about a fifth of protein.
Legumes and pulses: 46.2% of protein, 57.5% of lysine, 19.3% of energy. Grains and pasta: 38.4% of energy, 32.2% of protein, 21.6% of lysine. Novel alternatives: 21.0% of protein and 21.8% of lysine, with legume and pulse ingredients providing over 90% of that protein and lysine. · Contribution of food groups to nutrient profile
SuggestedPeople with too little lysine or leucine tended to have higher BMI and body fat, and lower energy intake and protein share of energy. The authors note this could reflect under-reporting of energy intake or a true intake deficiency.
Among those short on TID-adjusted lysine, 42% had BMI above the normal range and 85% had body fat in the overweight or obese range. For leucine the figures were about 50% and about 80%. Of those short on both, 56.6% were also below the protein EAR. Their protein share of energy was about 10.5%, near the lower bound of the 10 to 35% Acceptable Macronutrient Distribution Range (AMDR). · Comparison of TID-adjusted IAA intake to…; Exploration of body composition and its impact…
Methods, data and reproducibility
Cross-sectional analysis of four-day food diaries from 193 long-term NZ vegans. Protein came from FOODfiles and IAA profiles from matched USDA data, both scaled by literature TID coefficients for each food group. Intakes were compared with the EAR, the Recommended Dietary Intake (RDI), IAA scoring patterns and body-weight-based IAA requirements, followed by regression and a breakdown by food group.
- Four-day food diaries, anthropometry and DXA body composition from the cross-sectional Vegan Health Research Programme (Massey University, 2022 to 2023); adults vegan for at least two years · human · n = 193 analysed (52 males, 141 females) of 212 participants
- FOODfiles, the New Zealand reference food composition table (protein values)
- USDA food composition data for protein and IAA profiles, matched to reported foods
- True ileal digestibility coefficients from the literature, assigned by food group
- Food-group definitions from the 2008/2009 NZ Adult Nutrition Survey
- Methods & tools
- FoodWorks Professional (Xyris, 2022), FOODfiles, USDA food composition data, FAO/INFOODS food matching guidelines, R Studio 4.3.1, dual energy X-ray absorptiometry (DXA), Student's t-test, linear regression
- Reagents & environment
- R Studio version 4.3.1; FoodWorks Professional nutrient analysis software (Xyris, Australia, 2022).
- Reproducibility gaps
- The text has no code or data availability statement or links, and the TID coefficients for each food group are cited from the literature but not listed in the provided text.
Limitations (6)
- Literature TID coefficients are imprecise: many foods share one food-group value, not all preparation methods are distinguished, digestibility data for many fruits and vegetables are lacking, and tryptophan values are methodologically inconsistent. · stated by the authors
- Self-reported food diaries are prone to misreporting, especially under-reporting, which may explain the low energy intakes. Without a controlled feeding study, the misreported foods cannot be identified. · stated by the authors
- Protein was calculated with a fixed nitrogen-to-protein factor of 6.25, which assumes all proteins contain 16% nitrogen. · stated by the authors
- Females are over-represented (141 of 193) and had lower energy and protein intakes, which may bias cohort estimates. Plasma amino acid levels were not measured, so intake shortfalls are not linked to nutritional status. · stated by the authors
- The convenience sample is highly educated (over 80% with tertiary education) and mostly of European descent, and there is no omnivore comparison group, so contrasts with animal-protein diets rest on other studies. · noted in this summary
- IAA estimates rely on matching NZ foods to USDA entries, often via the highest-protein ingredient of each recipe, and the error from this matching is not quantified. Items under 0.5 g protein were excluded, though the remaining items still covered over 98% of cohort protein intake. · noted in this summary
Who should read:Read this if you assess dietary protein quality or model plant-based diets and want an example of applying true ileal digestibility coefficients to food-diary amino acid intakes in a vegan cohort.
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