A new study from researchers at Massey University in New Zealand has found that while most long-term vegans consume enough protein overall, many may not be getting enough of two essential amino acids—lysine and leucine.
These findings, published in PLOS ONE, raise important questions about how to maintain good nutritional balance on a fully plant-based diet.
Proteins are made of building blocks called amino acids. Our bodies can make many of these, but there are nine “indispensable” amino acids that we must get from the food we eat. Animal-based foods, like meat, eggs, and dairy, tend to contain all of these amino acids in the right amounts.
However, plant-based foods vary more widely in the types and amounts of amino acids they offer, which makes it harder—though not impossible—for people following a vegan diet to get everything they need.
The study looked at detailed food diaries from 193 adults in New Zealand who had been following vegan diets for a long time. Each participant tracked everything they ate over four days, and the researchers used national food databases to analyze how much protein and which amino acids they consumed.
They also took into account the fact that not all of the protein and amino acids in food are fully absorbed by the body. This is known as digestibility.
The good news: about 75% of participants met the recommended daily amount of total protein. When intake was adjusted for body weight, they also generally consumed enough of all nine indispensable amino acids.
But when the researchers factored in how well the body can actually absorb and use amino acids from plant sources, they found that only about half of the participants met the recommended intake for lysine and leucine.
These two amino acids are especially important—lysine plays a role in tissue growth and immune function, while leucine is vital for muscle repair and maintaining lean body mass.
Legumes (like beans and lentils) and pulses turned out to be the most important sources of both overall protein and lysine for the vegans in the study. Nuts and seeds also helped, but many other plant foods commonly eaten in vegan diets, such as grains and vegetables, are relatively low in lysine and leucine.
This study highlights an important point: just eating “enough protein” doesn’t guarantee that you’re getting the right types of protein. The researchers suggest that people on vegan diets should pay attention to the variety and combination of plant foods they eat to ensure they’re getting a full range of essential amino acids.
The lead author, Bi Xue Patricia Soh, noted that lysine and leucine were the most likely to be under-consumed in this group.
This could have health consequences over time, particularly for people who are older, physically active, or managing health conditions that increase protein needs. Prolonged shortages of these amino acids may affect muscle health, energy balance, and overall wellness.
Importantly, this doesn’t mean a vegan diet can’t be nutritionally complete—it just means that extra planning is often needed. Including a mix of legumes, lentils, soy products, nuts, and seeds can help improve the amino acid profile of plant-based meals.
In conclusion, this study shows that while most long-term vegans meet basic protein needs, many may still fall short in key amino acids, especially lysine and leucine.
Future research is needed to explore practical ways to boost these nutrients in vegan diets—perhaps through new food products, meal planning guides, or targeted supplements. For now, thoughtful food choices remain essential for those choosing a fully plant-based lifestyle.
If you care about nutrition, please read studies that vitamin D can help reduce inflammation, and vitamin K may lower your heart disease risk by a third.
For more health information, please see recent studies about foods that could sharp your brain, and results showing cooking food in this way may raise your risk of blindness.
The research findings can be found in PLOS ONE.
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