April 16, 2025

expert reaction to study of vegan protein consumption and amino acid intake

A study published in PLOS One looks at protein consumption and amino acid intake in vegan.

Prof Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London, said:

“Protein consists of mixtures of 20 amino acids and 8 of these are regarded as dietary essential because they cannot be synthesised from other amino acids in adults. This cross-sectional study has calculated the intakes of essential amino acids in adult vegans from food tables and compared them with reference intakes. The authors report that intakes of lysine and leucine are lower than reference amounts in vegans. 

“Limitations include:

1) There is no omnivore control group for comparison. 

2) The amino acid compositional data on foods were limited particularly on the amounts that may be digestible. 

3) No account was made of contribution by gut microbiota to dietary intake of lysine. 

4) Was the comparator reference intake appropriate? While vegans probably do have lower intakes of lysine and leucine it does not been the intakes suggest deficiency especially as the reference intakes are based mainly on American studies where intakes of protein were high and based mainly on animal products. 

“Interpretation of the results: 

“Human leucine deficiency has not been described. However, higher intakes have been promoted for body building in the form of whey protein. On the other hand, there is growing evidence that the growth promoting effects of high intakes of leucine and other branch chain amino acids may be linked to increased risk of cancer (especially prostate cancer). 

“In practice, protein requirements are estimated for the amounts required to maintain nitrogen balance and support growth. Although plant proteins when tested alone have a lower biological value than milk, eggs, meat and fish (measured by how they support growth in rats) when mixtures of plant proteins (e.g. cereals and pulses) are tested they have high biological value. In most human diets lysine is regarded as the amino acids most likely to limit protein quality. Physiological adaptations do occur on low protein intakes and lysine may be salvaged from lysine synthesised by gut microbiota in the large bowel.  This concept was supported by a recent study comparing vegans and omnivores (https://doi.org/10.1007/s00394-021-02790-y). That study measured plasma lysine concentrations did find levels to be 25% lower in vegans compared with omnivores but concluded the difference was unlikely to be of any significance.”

‘Evaluation of protein intake and protein quality in New Zealand vegans’ by Bi Xue Patricia Soh et al. was published in PLOS One at 19:00 UK time on Wednesday 16^th April.

DOI: https://doi.org/10.1371/journal.pone.0314889

Declared interests

Prof Tom Sanders: I have received grant funding for research on vegans in the past. I have been retired for 10 years but during my career at King’s College London, I formerly acted as consultant for companies that made artificial sweeteners and sugar substitutes.

I am a member of the Programme Advisory Committee of the Malaysia Palm Oil Board which involves the review of research projects proposed by the Malaysia government.

I also used to be a member of the Scientific Advisory Committee of the Global Dairy Platform up until 2015.

I did do some consultancy work on GRAS affirmation of high oleic palm oil for Archer Daniel Midland more than ten years ago.

My research group received oils and fats free of charge from Unilever and Archer Daniel Midland for our Food Standards Agency Research.

Tom was a member of the FAO/WHO Joint Expert Committee that recommended that trans fatty acids be removed from the human food chain.

Member of the Science Committee British Nutrition Foundation.  Honorary Nutritional Director HEART UK.

Before my retirement from King’s College London in 2014, I acted as a consultant to many companies and organisations involved in the manufacture of what are now designated ultraprocessed foods.

I used to be a consultant to the Breakfast Cereals Advisory Board of the Food and Drink Federation.

I used to be a consultant for aspartame more than a decade ago.

When I was doing research at King’ College London, the following applied: Tom does not hold any grants or have any consultancies with companies involved in the production or marketing of sugar-sweetened drinks.  In reference to previous funding to Tom’s institution: £4.5 million was donated to King’s College London by Tate & Lyle in 2006; this funding finished in 2011. This money was given to the College and was in recognition of the discovery of the artificial sweetener sucralose by Prof Hough at the Queen Elizabeth College (QEC), which merged with King’s College London. The Tate & Lyle grant paid for the Clinical Research Centre at St Thomas’ that is run by the Guy’s & St Thomas’ Trust, it was not used to fund research on sugar. Tate & Lyle sold their sugar interests to American Sugar so the brand Tate & Lyle still exists but it is no longer linked to the company Tate & Lyle PLC, which gave the money to King’s College London in 2006.”