Plant Proteins in Human Nutrition—Myths and Realities

Posted by Caroline Hodges on 14/1/2015

I am rather surprised to find many textbooks on nutrition and biochemistry still using phrases to describe vegetarian and vegan diets as lacking in ‘essential’ or ‘complete amino acids’. As far back as 1994, Young published the information listed below, but the majority of nutrition sites or textbooks still use the word ‘incomplete’ to describe proteins from vegetable sources, and I am wondering why.

This may be appropriate in some cases where dietary sources of protein are limited, but it is not so in most developed Western countries.

Furthermore if might also be worth considering that to the best of my knowledge, none of the current recommendations for protein intake allows for, or considers, the environmental impact of meat consumption in the West.

Myth Reality
Plant proteins are not complete; they lack certain amino acids Most dietary combinations of proteins are complete; certain food proteins may be low in specific amino acids.
Plant proteins are lower in quality than animal proteins. Protein quality depends not only on the source but also on the dietary mixture of plant proteins; plant proteins can be as high in quality as animal proteins.
Proteins from different plant foods must be carefully mixed and eaten together in the same meal. Proteins do not have to been eaten at the same meal; the mixture over a day is important for nutritional value.
Animal procedures can provide good indices of the human nutritional value of food proteins. Animal procedures may underestimate plant protein quality for humans and have overestimated human requirements
Plant proteins are difficult to digest. Depending on the source and method of food preparation, plant proteins can be easy to digest.
People cannot meet protein needs with plant proteins alone. Plant protein or animal protein can provide adequate protein for human needs.
Plant proteins are lacking in nutritional value because they are not balanced. Plant proteins do not create a practical problem in terms of balance; possible imbalances are observed in amino acid supplementation.

*Studies show the average requirement = 0.66 g /kg body weight

Safe and adequate level of intake = 0.825 g /kg body weight (UK average = 1.2)

Safe and adequate level of intake = 8% of energy intake (UK average = 15)

Table adapted from:

Young VR, Pellett PL. Plant proteins in relation to human protein and amino acid nutrition. Am J Clin Nutr. 1994; 59(suppl):1203S–1212S.


The 2009 American Dietetic Association’s Position Paper on Vegetarian Diets says:

“Plant protein can meet requirements when a variety of plant foods is consumed and energy needs are met. Research indicates that an assortment of plant foods eaten over the course of a day can provide all essential amino acids and ensure adequate nitrogen retention and use in healthy adults, thus complementary proteins do not need to be consumed at the same meal.”

If you go to the USDA Database Standard Reference 25 and look up the analysis of any one whole plant food, you will see that all the amino acids exist in the food.

I would appreciate anyone’s feedback please.


2 thoughts on “Plant Proteins in Human Nutrition—Myths and Realities

  1. Pingback: The Great Protein Fiasco? Understanding Plant Proteins in Human Nutrition | Brighton and Sussex Universities Food Network

  2. André

    As trusting humans, we have been duped my cartels of ill repute, backed by their lackeys in Government, who disgracefully bow down to an agricultural lobby, hell bent on spreading lies.
    This is purely for profit and nothing to do with the metabolic or health needs of a nation.
    Exploiting animals to vile and cruel practises, some, in these cartels, should be in a jail for cruelty on a massive scale, the most of which is arrogantly ignored by those in power.
    The most powerful and strong creatures on earth do not need animal protein either to grow, or to perform phenomenal feats of strength and neither do humans.
    As a life long vegetarian who works as a labourer, I have experiential proof that a plant based diet suffices perfectly well. I don’t need false industry paid for research, I have my life as proof.


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