People on vegan diets may be missing key muscle-building nutrients, even if their total protein intake seems sufficient, claims a new study.
Researchers in New Zealand found that some long-term vegans lacked essential amino acids – the building blocks of protein – which could have implications for overall nutrition.
Proteins are made up of amino acids, nine of which are considered “indispensable” because our bodies can’t produce them. These include lysine and leucine, both vital for healthy growth, energy production, and muscle repair.
The study, published in the journal PLOS One, analysed four-day food diaries from 193 long-term vegans.
Researchers found that while around 75 per cent of participants met recommended daily protein levels, only about half were getting enough lysine and leucine once protein digestibility was taken into account.
“Vegan diets are the most restrictive form of plant-based eating, relying entirely on plant sources for all nutrients,” the authors of the study said.
“Achieving high protein quality on a vegan diet requires more than just consuming enough protein – it also depends on the right balance and variety of plant foods to supply all the amino acids in the quantities that our body needs.”
Lysine is crucial for healthy growth and plays a key role in producing carnitine – a nutrient that helps convert fatty acids into energy and supports cholesterol regulation.
Leucine, meanwhile, also supports growth, helps muscles recover and even plays a role in weight control.
But before you start rethinking that steak, it’s worth considering the limitations of the study.
“I think you know it's a useful study that looks at adequacy of protein in people consuming a vegan diet,” Prof Shireen Kassam, an expert on plant-based nutrition at the University of Winchesterm, UK, told BBC Science Focus.
“But like many of these things, this study is one snapshot in time, with people being asked to recall what they consumed – it’s self-reported data that may or may not reflect how the diet is affecting health.”
She also pointed out that the digestibility of amino acids was estimated using animal models and that more accurate insights could have come from directly measuring amino acid levels in the blood.
Moreover, the study didn’t compare the vegan participants to people following omnivorous or vegetarian diets.
So, what’s the takeaway for vegans? Variety and quality matter just as much as quantity when it comes to protein. “The trick is having a diet that prioritises high-quality sources of plant proteins like legumes – beans, pulses, and soya foods like tofu, tempeh and edamame,” Kassam said.
About our expert
Shireen Kassam is a Consultant Haematologist and Honorary Senior Lecturer at King’s College Hospital, London, with a specialist interest in the treatment of lymphoma. She is also a visiting professor at the University of Winchester, Hampshire, where she has developed and facilitates the UK's first University-based course on plant-based nutrition.
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