A comprehensive new study conducted by researchers at Massey University, New Zealand, sheds light on a crucial but often overlooked element of vegan nutrition: not just total protein intake, but the quality and bioavailability of protein in long-term vegan diets. Published in PLOS One on April 16, 2025, this observational research addresses a critical nuance in vegan dietary patterns that could have significant implications for health outcomes among vegans worldwide. While most individuals on plant-based diets achieve adequate total protein consumption, this groundbreaking investigation reveals that many fail to meet essential amino acid requirements, especially for lysine and leucine, which are vital for various physiological processes.
Proteins consist of amino acids, the fundamental molecular blocks that perform diverse biological functions. Although the human body can synthesize some amino acids, nine indispensable amino acids cannot be produced internally and thus must be obtained through diet. For vegans, sourcing these amino acids presents a unique challenge because plant-based foods naturally vary in their amino acid profiles and digestibility. This study emphasizes the fact that a simple tally of protein grams consumed is insufficient to evaluate protein adequacy; rather, a detailed assessment of amino acid quality and their bioavailability in vegan diets is crucial.
Traditional assessments of dietary protein often neglect the digestibility factor—how much of the consumed protein and its constituent amino acids can actually be absorbed and utilized by the body. Soh and colleagues bridged this gap by meticulously analyzing detailed, four-day food diaries from 193 long-term vegans residing in New Zealand. By leveraging nutrient databases from both the USDA and New Zealand FoodFiles, the team was able to estimate not only the total protein but also the individual indispensable amino acids consumed by participants. This dual approach provides a more nuanced understanding of protein quality in actual vegan eating patterns.
Their findings revealed that about 75% of the participants consumed enough total protein daily when adjusted for body weight. At a glance, this might be reassuring, confirming previous beliefs that vegan diets can supply ample protein. However, when the researchers accounted for protein digestibility—using established protein digestibility-corrected amino acid scores (PDCAAS) and related methods—the picture became less optimistic. Only about half of the vegans met daily requirements for lysine and leucine, two indispensable amino acids that are often the limiting factors in plant-based diets.
Lysine and leucine play irreplaceable roles in the human body. Lysine is fundamental for protein synthesis, hormone production, and calcium absorption, while leucine is a key regulator of muscle protein synthesis and metabolic homeostasis. Deficiencies in these amino acids over time can impair muscle maintenance, immune function, and overall physiological resilience. The study underscores that insufficient lysine and leucine intake among vegans could have tangible implications, particularly for vulnerable groups such as the elderly, pregnant women, or individuals recovering from illness.
One striking element of this research is the variation in dietary patterns among vegans, illustrated via three hypothetical vegans—Mandy, Jerry, and Sandy. Mandy represents an optimal dietary approach achieving both high total protein and sufficient amino acid quality by incorporating diverse plant proteins. Jerry meets his protein quantity but falls behind in quality, while Sandy exemplifies a common pattern with inadequate protein amounts and quality. This characterization of real-world vegan diets highlights the diversity within plant-based eating and how dietary choices impact nutritional outcomes.
Data analysis pinpointed legumes and pulses as the predominant sources of both total protein and lysine intake. These food groups are rich in indispensable amino acids and more digestible than many other plant sources. However, a reliance on cereals and starch-heavy foods without balancing adequate legumes seems to be a common dietary pitfall leading to amino acid insufficiencies, as observed in the cohort. The researchers advocate for strategic dietary planning, encouraging vegans to integrate a variety of legumes, nuts, and seeds to remedy amino acid shortfalls in a balanced and palatable way.
This study also challenges the conventional wisdom that total protein readings alone reflect nutritional adequacy in vegan diets. The discrepancy between protein quantity and quality demands a paradigm shift in how vegan nutrition is assessed and managed. Adequate protein quality involves consuming complementary plant foods whose amino acid profiles synergistically fulfill bodily demands. It is not merely about how much protein is eaten, but which proteins and in what combinations.
The implications for public health and clinical practice are substantial. Nutritionists working with vegan clients must emphasize amino acid quality and digestibility, guiding food selections beyond raw protein counts. Moreover, fortified foods or supplementation might become necessary for individuals unable to meet amino acid requirements through whole foods alone. The research urges further exploration into tailored interventions and policies supporting sustainable, nutritionally adequate vegan diets.
Soh and the team conclude that while vegetarian and vegan diets offer numerous benefits, including reduced environmental impacts and lower chronic disease risks, attention to indispensable amino acid intake remains critical. Vegan diets "require more than just consuming enough protein," they note, "it also depends on the right balance and variety of plant foods." Without this, prolonged nutritional gaps could undermine muscle preservation, immune function, and metabolic health, especially in vulnerable populations or those with increased physiological demands.
This study’s open-access status affords researchers, clinicians, and the public the opportunity to scrutinize and build upon its findings. By refining our understanding of protein quality in plant-based diets, this research contributes to more scientifically accurate dietary recommendations and furthers the global discourse on sustainable nutrition. Future investigations will need to devise practical strategies to elevate lysine and leucine intake across vegan populations to safeguard health and well-being.
In summary, this pivotal research highlights an essential nuance in vegan nutrition—protein quality assessment must move beyond total quantities to encompass amino acid digestibility and adequacy. By doing so, the scientific and health communities can better support individuals who choose veganism to thrive nutritionally without compromising their ethical values or health objectives. As the world increasingly embraces plant-based diets, these findings could catalyze a vital evolution in nutritional science and dietary guidance.
Subject of Research: People
Article Title: Evaluation of protein intake and protein quality in New Zealand vegans
News Publication Date: 16-Apr-2025
Web References: http://dx.doi.org/10.1371/journal.pone.0314889
References: Soh BXP, Vignes M, Smith NW, von Hurst PR, McNabb WC (2025) Evaluation of protein intake and protein quality in New Zealand vegans. PLoS ONE 20(4): e0314889.
Image Credits: Soh et al., CC-BY 4.0
Keywords: vegan diet, protein quality, indispensable amino acids, lysine deficiency, leucine intake, plant-based nutrition, protein digestibility, amino acid bioavailability, long-term vegans, nutritional adequacy
