A new study has found that while most long-term vegans consume enough total protein, many fall short when it comes to key amino acids vital for health—particularly lysine and leucine. The research, published in PLOS One on April 16, 2025, was conducted by Bi Xue Patricia Soh and colleagues at Massey University in New Zealand.
Why Amino Acids Matter
Proteins are made of amino acids, the fundamental building blocks the body uses for numerous functions, including tissue repair and enzyme production. While the human body can make some amino acids on its own, nine indispensable amino acids must be obtained through diet.
Unlike animal-based proteins—which are typically complete and rich in all indispensable amino acids—plant-based foods often vary widely in amino acid composition. This variation can make it challenging for vegans to meet their needs without careful dietary planning.
The Study at a Glance
Researchers analyzed four-day food diaries from 193 long-term vegans in New Zealand. They assessed protein and amino acid intake using nutritional data from the USDA and the New Zealand FoodFiles database. The study went beyond simple protein intake, evaluating how much of the amino acids were actually digestible and absorbable—a factor often overlooked in prior research.
Key Findings:
75% of participants met the total daily protein requirements.
All nine indispensable amino acids were consumed in adequate amounts before considering digestibility.
Once digestibility was factored in, only about half of the participants met the daily requirements for lysine and leucine.
These two amino acids—especially critical for muscle repair, immune function, and protein synthesis—were found to be the most limiting in vegan diets.
Major Food Contributors
Among the foods eaten by participants, legumes and pulses (such as lentils, beans, and chickpeas) were the largest contributors to both total protein and lysine intake. However, even these rich sources weren’t always enough to meet daily digestible thresholds, particularly for people with higher protein demands.
Implications and Next Steps
This study shows that protein quality, not just quantity, should be a central focus in vegan dietary planning. Simply eating enough protein doesn’t guarantee that all essential amino acid needs are being met.
The authors recommend further research to:
Develop nutritionally balanced vegan meal plans that ensure adequate lysine and leucine intake.
Explore plant-based protein combinations that optimize amino acid profiles.
Investigate whether supplementation or fortified foods could play a role for high-risk individuals, such as athletes or children.
Conclusion
For vegans, this study is a timely reminder to think beyond grams of protein and focus on amino acid diversity and digestibility. Thoughtful choices—especially around legumes and varied plant proteins—can go a long way in maintaining a nutritionally complete diet.
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