• Even if vegans achieve their daily protein targets, they might not obtain sufficient amounts of some crucial amino acids, recent studies suggest.
  • This research underscores the significant role of protein quality, beyond mere quantity, in fulfilling nutritional requirements.
  • Most plant-based proteins do not digest as easily as animal proteins and often lack one or more essential amino acids in adequate concentrations.

Recent findings indicate that vegans, despite consuming enough protein, might not receive adequate levels of certain critical amino acids.

A recent study, published in the journal PLOS ONE on April 16, shifted focus from the overall protein intake to the specific amino acids and their digestibility. The study revealed that about half of the participants did not meet the necessary levels of lysine and leucine.

The research emphasizes the importance of considering not only the total protein intake but also the quality of protein and its amino acid profile in a vegan diet.

Amino acids serve as the protein’s building blocks. Although the body can synthesize some amino acids, nine essential ones must be ingested through diet.

Previously, plant-based proteins were considered “incomplete” as they were lacking in certain essential amino acids. However, it’s now recognized that they contain all essential amino acids, albeit sometimes at suboptimal levels compared to animal-derived proteins.

To adequately meet their essential amino acid needs, those on a vegan diet need to strategically consume a diverse range of foods such as nuts and legumes.

“Consuming 30 grams of a lower-quality plant protein like wheat differs significantly from consuming an equal amount of a higher-quality protein like soy,” explained Bi Xue Patricia Soh, MSc, the study’s lead author and a PhD fellow with The Sustainable Nutrition Initiative Team at the Riddet Institute, Massey University, New Zealand.

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“Thus, our results demonstrate that meeting the overall protein requirement doesn’t necessarily equate to adequate protein quality, particularly in terms of lysine and leucine, which are essential for various body functions,” Soh stated to Healthline.

Half of Participants Lack Adequate Amino Acids

Soh and her team conducted an extensive study involving 193 long-term vegans in New Zealand, comprising 141 women and 52 men.

The participants were healthy adults who had adhered to a vegan diet for over two years. They provided detailed four-day food diaries that documented every food, drink, and supplement they consumed.

The analysis was refined by adjusting for protein digestibility, which assesses how effectively the body can break down and absorb proteins and amino acids from different sources.

Post-adjustment, while a majority of participants met their overall protein needs—78.8% of males and 73.0% of females—a significant number still fell short on lysine and leucine.

For instance, soy protein, known for its high digestibility among plant foods, allows nearly complete nutrient utilization by the body. Conversely, wheat protein is less digestible, influenced by antinutrients among other factors.

This crucial distinction highlights how some evaluations of plant-based diets might overestimate the actual protein availability, a fact corroborated by this study’s findings.

After accounting for digestibility, about one-quarter of the participants did not meet their overall protein requirements. More specifically, only 43.5% met their digestible leucine needs, and just 56% consumed sufficient digestible lysine.

However, the study noted that all other essential amino acids were generally present in adequate amounts after considering digestibility.

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The Nine Essential Amino Acids

The essential amino acids necessary for human health are:

  • phenylalanine
  • valine
  • threonine
  • tryptophan
  • methionine
  • leucine
  • isoleucine
  • lysine
  • histidine

As the body cannot produce these amino acids, it is critical to consume a balanced diet, especially when following a vegan lifestyle.

“Essential amino acids are vital for overall health, and a prolonged deficiency can lead to negative health impacts,” Kristin Kirkpatrick, MS, RD, a nutritionist at the Cleveland Clinic and co-author of “Regenerative Health,” informed Healthline.

These amino acids are crucial for various bodily functions including muscle growth stimulation, fat metabolism, immune system support, sleep regulation, appetite control, blood sugar management, and calcium absorption.

“Lysine and leucine, in particular, are important for maintaining healthy bones, muscle mass, and facilitating DNA methylation. Leucine plays a significant role in cellular pathways that regulate muscle protein synthesis,” Soh added.

Strategies for a Nutritious Vegan Diet

“A simple and effective approach is to ensure a variety of plant proteins are included in all three daily meals, supplemented with one or two protein-rich snacks like nuts, seeds, or protein shakes that have high amino acid digestibility,” Soh recommended.

The study indicated that legumes and pulses such as edamame, black beans, chickpeas, and lentils were leading sources of digestible protein and lysine.

While numerous plant-based protein sources are available, including fruits, vegetables, grains, and non-dairy milks, they all contribute to the daily intake of essential amino acids.

“Achieving adequate protein levels is crucial, but a well-rounded diet rich in fiber and other nutrients is equally important,” Alyssa Kwan, MS, RD, a clinical dietitian in cardiology at Stanford Medicine, not involved in the study, told Healthline.

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Unlike proteins derived from animal sources, which naturally contain all nine essential amino acids, plant proteins often require combining to meet nutritional standards.

However, it’s not necessary to combine specific foods at every meal. Eating a variety of plant-based proteins throughout the day and focusing on high-quality sources like beans and soy products can help fulfill essential amino acid requirements.

Kwan emphasized that dietary assessment should be holistic, focusing less on individual components and more on overall dietary patterns.

“I don’t believe it’s necessary to target specific amino acids like lysine or leucine. Focusing on high-fiber, high-protein plant-based foods should address any gaps in essential amino acids,” she explained.

Kirkpatrick also pointed out that following a vegan diet doesn’t automatically ensure balanced nutrition. Making informed food choices is essential.

“Some vegan patients I’ve seen started independently and often made choices that were not nutritionally sound. This could involve opting for ultra-processed vegan items, neglecting nutrient density, or lacking awareness about when supplements might be necessary,” she concluded.