Complete protein vs incomplete: 3 common myths. Picture of animal proteins and plant proteins. Veg Out With Maria.

Surprisingly, the debate over complete proteins versus incomplete proteins has persisted for decades and continues to be clouded by misconceptions and myths – even among educated healthcare professionals.

Animal protein is usually thought to be a “complete” protein source while most plant-based protein sources are looked down upon as being “incomplete.” However, it’s important to uncover the truth and put the debate to rest, especially for those attempting to eat more plant-based.

In this blog, we’ll cover what is considered a “complete” protein and debunk three common myths surrounding complete and incomplete proteins and how you can ensure you are meeting your protein needs.

What is a Complete Protein?

The protein that you eat is made up of “building blocks” called amino acids. There are a total of 20 amino acids, 11 are made by the body (non-essential). The remaining nine are what we call “essential” amino acids, meaning that your body cannot make these, so you need to obtain them from your diet.

These essential amino acids are crucial for various bodily functions, including muscle building, tissue repair, and immune system function.

The following 9 amino acids are considered essential:

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

Historically, a food is considered a “complete” protein when it contains all nine essential amino acids in relatively the same amounts.

Animal proteins such as meat, fish, eggs, and dairy are usually classified as complete proteins because they contain all 9 essential amino acids in what appears to be optimal amounts. However, this classification system is very misleading which leads us to the first myth.

Myth 1: Plant Proteins Are Incomplete

Scrabble tiles spelling Quest. Plant proteins are not incomplete proteins. Veg Out With Maria

A common myth – even to this day – is that in contrast to animal proteins, most plant proteins are lacking at least one essential amino acid, therefore making them “incomplete” proteins. However, this is just not true.

All plant foods contain all 20 amino acids, including all 9 essential amino acids!1 The difference with most plant proteins is that at least one of the amino acids is lower in proportion to the other amino acids.

For instance, grains are lower in lysine, and beans are lower in methionine. They are not missing these amino acids, the amounts are just smaller than what is considered optimal to meet your daily requirements. But, how relevant is this?

All protein-containing foods – including animal sources – do not contain equal proportions of the 20 amino acids. This is because our bodies do not need the same amount of each amino acid.

I love how Christopher Gardner, PhD compares it to the game of Scrabble. You don’t have exactly the same amount of tiles for the letters A, E, Q, and Z. There are more As and Es than there are Qs and Zs because we use them more in the English language. The same goes for amino acids.

Now, if you were to only eat rice or only beans for the entire day then you would be deficient in either lysine or methionine. But, this is not how we eat – at least not in developed countries. We eat a variety of foods in a day and, in general, we tend to consume well over the RDA for protein, easily meeting our daily requirements for all amino acids.

Plant Protein Superstars

There are, however, a few plant proteins that have a good amount of all the essential amino acids. Some of these “complete” plant proteins include:

  • Soy foods like tofu, tempeh, edamame, and miso
  • Quinoa
  • Buckwheat
  • Amaranth
  • Chia seeds
  • Hemp seeds
  • Spirulina
  • Nutritional Yeast
  • Ezekiel bread (because it is made from both sprouted grains. soybeans and lentils)

Myth 2: You Need To Combine Plant Proteins

a bowl of rice and beans. Complete protein.

The theory of needing to combine or “complement” plant proteins with each meal to ensure you get all of your essential amino acids surfaced back in the 70’s. It was popularized by a book written in 1971 called Diet for a Small Planet, by Frances Moore Lappé.

However, the author later retracted her position on the need for protein combining. She validated the fact that all plant foods contain all the essential amino acids.

She also stated that as long as you were consuming enough calories it was almost certain you would be able to meet all your protein needs from plant sources. The myth, however, seems to continue.

Your body cannot store protein the same way that carbohydrates and fats are stored. But, you do have this cool “free amino acid pool” to pull from instead.

The body maintains a small pool of amino acids that can be used for protein synthesis and other metabolic processes2,3. When you eat protein, it is broken down into individual amino acids during digestion and absorbed into the bloodstream. These amino acids can then be used to replenish the amino acid pool in the body.

This pool is constantly being replenished through the digestion of dietary protein, the non-essential amino acids synthesized in the liver, and the recycling of existing proteins in the body.

At the end of the day, as long as you are eating enough calories and incorporating a variety of plant foods in your diet, your body can take what it needs and you do not have to worry about combining!

Myth 3: It’s Difficult To Get Enough Quality Protein On A Plant-Based Diet

women laughing eating salad

Another myth is that vegetarians and vegans have a hard time getting enough quality protein in their diet. Well, thankfully plant-based eaters don’t survive on salad alone!

To date, there is no evidence of protein deficiency in vegetarian populations in Western countries1. An exception would be if you are not eating enough total calories or what you do eat provides little variety and is low in total protein.

People who are on super restrictive diets or the elderly with poor appetites would be populations at risk for this.

Another argument has to do with protein digestibility and that animal protein is much easier to absorb than plant protein. However, the two main methods used for measuring protein digestibility (PDCAAS and DIAAS) both have their limitations4,5.

In reality, most of us don’t eat protein in isolation or from only one food source. When considering the diet as a whole, if you are consuming enough calories and including variety, you can easily get enough quality protein on a plant-based diet. If you fall into one of the populations at risk then I would concentrate on choosing more from the plant protein superstars above.

Quality of Your Overall Diet

What really matters is the quality of your overall diet. When you include more vegetables, fruit, whole grains, legumes, soy foods, nuts and seeds in your diet you are including more fiber, phytochemicals, antioxidants, and nutrients. This, in combination with reducing saturated fat intake, has a positive impact on your overall health!

There are nutrients of concern, however, when following a plant-based diet such as vitamin B12 that warrant taking in supplement form. Refer to the blog Key Blood Tests For Vegans for a more detailed list.

Despite this, studies have shown that those with greater amounts of plant protein intake vs animal protein were associated with lower cardiovascular and overall-cause mortality6.

Vegetarians and vegans have also been found to have a reduced risk of heart disease, type 2 diabetes, high blood pressure, certain types of cancer, and obesity7.

Bottom Line

I think it is safe to say that we don’t have to worry about plant-based eaters dying from protein deficiency! It’s time we put the debate over complete vs incomplete protein and the need to combine proteins to rest.

Plant proteins like soy foods (tofu, tempeh, soy milk, edamame), seitan, beans and lentils (my fav!) contain high amounts of protein. You can also find protein in nuts and seeds, whole grains, and vegetables.

If you are eating enough calories and including a variety of plant foods in your diet then you are most likely meeting your protein needs.

For more guidance on how to put together a balanced plant-based meal check out the Supplement and Micronutrient Guide. It includes a plant-based food plate guide that shows you how to eat balanced meals to ensure you are satisfied and getting the right variety of nutrients in your diet.

Leave a Comment

Your email address will not be published. Required fields are marked *