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Debunking the ‘Incomplete’ Protein Myth : A Comprehensive Guide to Plant-Based Proteins

Many of us are under the impression that the proteins derived from plants are inferior to animal proteins. This is why plant proteins are often referred to as “incomplete” proteins. This causes fear mongering among health conscious people that the type and the quality of the protein, which they are getting is not good which is sourced from vegetables.

In this article we will talk about different reasons why this is considered as a myth and debunk this myth and will discuss the truth about incomplete proteins.

We will differentiate “incomplete” and “complete” proteins and why people who are vegans or vegetarians need not fear that they are getting insufficient protein.

What is Meant By ‘Incomplete’ Proteins?

Amino acids are the building blocks which constitute proteins. There are several forms of amino acids; however, only 20 are required to manufacture the ones present in the body. These are then divided into three primary categories.(1)

Essential amino acids comprise of nine amino acids, which cannot be made by the body. The only way to get them is through diet.

Non-essential amino acids consist of the remaining 11 amino acids that the body can often manufacture from the 9 essential amino acids.

Conditionally essential amino acids are often thought of as non-essential; however, turn into essential during pregnancy, adolescence or under certain situations, such as illness or trauma.

Foods which have sufficient quantities of these nine essential amino acids are usually thought of as sources of “complete” protein and those which do not, are referred to as “incomplete” protein.

Which Foods are Sources of ‘Incomplete’ Proteins?

It is not known, but both the plant and animal based proteins do have all the nine essential amino acids. The only difference being the quantities they contain. For example eggs, fish, meat and dairy have increased quantities of all the nine essential amino acids. Whereas plants have lesser amount of a minimum of one or two essential amino acids according to the group to which they belong.

For example, veggies and legumes have quantities of cysteine and methionine; whereas nuts grains and seeds will have lysine in lesser amounts.(2)

This means that consumption of either of the diets gives very less of either food group resulting in insufficient intake of essential amino acids. This is the reason why animal-based foods are usually considered as “complete” sources of protein and majority of the plant-based foods are referred to as “incomplete.”

However, there are some exceptions, such as quinoa, soy, buckwheat, amaranth and nutritional yeast, as well as chia and hemp seeds, where there are sufficient amounts of all the nine essential amino acids and is thought to be “complete” sources of plant protein.

Can a vegan or vegetarian diet provide sufficient ‘complete’ proteins?

It is a common belief that vegetarian and vegan diets have decreased amount of animal-based protein and hence they lack enough quantities of “complete” protein. However, this is very seldom the reality and there are few exceptions to it. As of now, there’s no evidence of deficiency of protein in people following vegan or vegetarian diet barring a few who consume very less calories or follow a restricted or monotonous patterns of eating, such as potato-based or fruitarian diets.(3)

Nevertheless, the protein present in plants can be a tad bit difficult for the body to absorb, when compared to the protein present in animal-based foods. This is the reason vegans and vegetarians are usually encouraged to consume slightly more protein than people who consume meat, which is around 0.5 grams per pound in a day.(4)

However, according to the current evidence, this difference in protein absorption is not that much to cause vegans or vegetarians to get insufficient quantities of essential amino acids from their diet.(3)

In conclusion, as long as a plant-based diet has enough calories and contains variety of sources of protein, there is no need to worry of less “complete” protein on a vegan or vegetarian diet.


Foods that are rich in protein and have sufficient amounts of all the nine essential amino acids are usually considered “complete” protein sources and which don’t contain the 9 essential amino acids are referred to as “incomplete” sources of protein. This is the reason why many plant foods are thought to be “incomplete” proteins, leading to the formation of the myth that plant-based diets cannot provide sufficient amount or form of protein.

To sum up this article, if the plant-based diet contains sufficient calories and good variety of food groups, then it can provide sufficient or complete proteins so, in fact there is nothing to worry for the vegans or vegetarians with regards to being on the receiving end of “incomplete” proteins.


Team PainAssist
Team PainAssist
Written, Edited or Reviewed By: Team PainAssist, Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:September 9, 2023

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