Complementary Protein Myth Won't Go Away!

Written by Dr. Fuhrman’s colleague Jeff Novick, M.S., R. D. for the May 2003 edition of Healthy Times:

Recently, I was teaching a nutrition class and describing the adequacy of plant-based diets to meet human nutritional needs. A woman raised her hand and stated, “I’ve read that because plant foods don’t contain all the essential amino acids that humans need, to be healthy we must either eat animal protein or combine certain plant foods with others in order to ensure that we get complete proteins.”

I was a little surprised to hear this, since this is one of the oldest myths related to vegetarianism and was disproved long ago. When I pointed this out, the woman identified herself as a medical resident and stated that her current textbook in human physiology states this and that in her classes, her professors have emphasized this point.

I was shocked. If myths like this not only abound in the general population, but also in the medical community, how can anyone ever learn how to eat healthfully? It is important to correct this misinformation because many people are afraid to follow healthful, plant-based, and/or total vegetarian (vegan) diets because they worry about “incomplete proteins” from plant sources.

How did this “incomplete protein” myth become so widespread?

No small misconception

The “incomplete protein” myth was inadvertently promoted in the 1971 book, Diet for a Small Planet, by Frances Moore Lappe. In it, the author stated that plant foods do not contain all the essential amino acids, so in order to be a healthy vegetarian, you needed to eat a combination of certain plant foods in order to get all of the essential amino acids. It was called the theory of “protein complementing.”

Frances Moore Lappe certainly meant no harm, and her mistake was somewhat understandable. She was not a nutritionist, physiologist, or medical doctor. She was a sociologist trying to end world hunger. She realized that there was a lot of waste in converting vegetable protein into animal protein, and she calculated that if people just ate the plant protein, many more people could be fed. In a later edition of her book (1991), she retracted her statement and basically said that in trying to end one myth—the unsolvable inevitability of world hunger, she created a second one—the myth of the need for “protein complementing.”

In these later editions, she corrects her earlier mistake and clearly states that all plant foods typically consumed as sources of protein contain all the essential amino acids, and that humans are virtually certain of getting enough protein from plant sources if they consume sufficient calories.

Amino acid requirements
Where did the concept of “essential amino acids” come from? In 1952, William Rose and his colleagues completed research that determined the human requirements for the eight essential amino acids. They set the “minimum amino acid requirement” by making it equal to the greatest amount required by any single person in their study. To set the “recommended amino acid requirement,” they simply doubled the minimum requirements. This “recommended amino acid requirement” was considered a “definitely safe intake.”

Today, if you calculate the amount of each essential amino acid provided by unprocessed plant foods and compare these values with those determined by Rose, you will find that any single one, or combination, of these whole natural plant foods provides all of the essential amino acids. Furthermore, these whole natural plant foods provide not just the “minimum requirements” but provide amounts far greater than the “recommended requirements.”

Modern researchers know that it is virtually impossible to design a calorie-sufficient diet based on unprocessed whole natural plant foods that is deficient in any of the amino acids. (The only possible exception could be a diet based solely on fruit.)

Pride and prejudice
Unfortunately, the “incomplete protein” myth seems unwilling to die. In an October 2001 article in the medical journal Circulation on the hazards of high-protein diets, the Nutrition Committee of the American Heart Association wrote, “Although plant proteins form a large part of the human diet, most are deficient in one or more essential amino acids and are therefore regarded as incomplete proteins.”1 Oops!

Medical doctor and writer John McDougall wrote to the editor pointing out the mistake. But in a stunning example of avoiding science for convenience, instead of acknowledging their mistake, Barbara Howard, Ph.D., head of the Nutrition Committee, replied on June 25, 2002 to Dr. McDougall’s letter and stated (without a single scientific reference) that the committee was right and “most (plant foods) are deficient in one or more essential amino acids.” Clearly, the committee did not want to be confused by the facts.

Maybe you are not surprised by this misconception in the medical community. But what about the vegetarian community?

Behind the times
Believe it or not, an article in the September 2002 issue of Vegetarian Times made the same mistake. In a story titled “Amazing Aminos,” author Susan Belsinger incorrectly stated, “Incomplete proteins, which contain some but not all of the EAAs [essential amino acids], can be found in beans, legumes, grains, nuts and green leafy vegetables.... But because these foods do not contain all of the EAAs, vegetarians have to be smart about what they eat, consuming a combination of foods from the different food groups. This is called food combining.”

A dangerous myth
To wrongly suggest people need to eat animal protein for nutrients will encourage them to add foods that are known to contribute to the incidence of heart disease, diabetes, obesity, and many forms of cancer, to name just a few common problems.


1. Circulation 2001;104: 1869-74.

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Comments (11) Read through and enter the discussion with the form at the end
Bree - February 9, 2007 2:40 PM

I am looking for the reference to support this information to prove it to someone who does not believe me. The "Circulation" source listed is missing which month the article was in. Any other sources for this would be great too.

Kelly - February 13, 2007 6:01 PM

Where is the proof that this is a myth?
I just looked up several plant foods on a nutritional analysis website. It gives the AA content of each plant food, and as I was taught, several of them were defiecient in one or more AA.
If this is a myth, where can I find accurate AA content of plant proteins? How come so many textbooks and research articles still talk about incomplete proteins if it is such a false science?

Claudia - February 18, 2007 12:38 PM

The 8 essential and 12 non-essential amino acids occur in varying proportions in each of the plant foods. The fact that you looked up several plant foods and found that they had a lower proportion of several AAs does not mean that it would constitute a deficiency in terms of human nutrition. In other words, the point is that if a great enough quantity is eaten to satisfy caloric needs, then the protein needs would automatically be met. Here is some more information on this which is complete with references:

Dr. McDougall's debate with the AHA in the Correspondence section of 'Circulation':

Info from the VegSource website:

Sam - March 18, 2007 9:15 PM

Thank you so much for doing your part to dispel this myth. I imagine the meat industry has done its share to see it taught for as long as it has.

My only concern would be a hope for some references to nutritional assays in articles, etc. This would be the next step in supplanting the established theory.


Annie - March 15, 2009 12:03 PM

I'm not surprised at all that this is still being taught in school. I took a nutrition course for nursing school and they are still saying that formula is just as good for babies as breast milk - it's just a matter of choice. It's a shame that we live in a society where lobbiests have a say in what gets put into our textbooks.
Next thing you know, they'll want to start teaching religion in science class!! Oh, wait.....

Vicki Louise - April 5, 2009 12:42 PM

It's amazing how so many people gain the ear of the public and espouse to know more than what is FACT. How often do we hear of others who try and try to educate people as to what they know to be true, show how strongly they believe in it and yet no one seems to listen. They rant and chant and speak louder if others don't believe. Strangely, if you rant loudly, many more will beleive. Volume matters. Time and time again. Snake oil and magic waters; when will they learn?

Technology is so important, but it does not change how some individuals think and act and claim to know the "truth". Technology helps us discover the truth better than we could have 150 or more years ago, when snake oil salesmen were common in western towns, riding in with their horse-drawn wagons filled with crates of bottles of magic water or snake oil, claiming amazing cures - and people bought it. We still have that type of person, yet, with technology it is so easy to see through their, well, lack of knowledge or understanding or adequate training.

Some colleges are teaching that if an individual is placed on a diet low in certain amino acids, such as the various amino acids which are lacking in high protein plant foods, there is "no problem" since measurements of amino acids found in blood are found to be in normal levels after a short period of time. Therefore, how could Anyone think that you need to use complimentary proteins, since the body obviously shows no signs of lacking the amino acids which are lacking in their diet?

Because our body will digest itself in order to get the amino acids it can't get from the diet! That is how we find "Essential" amino acids in our blood regardless of our current diet. Those amino acids come from plant food which we had already eaten, when either we ate the plant or the cow did, before the person started the diet.

As far as our body digesting itself, muscle, for example, has a lower priority than enzymes and some hormones (both made from amino acids), because we die without those enzymes and hormones. We don't die without our muscles. Or do we?

Heart muscle is not spared the self-digestive process and heart muscle that gets broken down CANNOT be replaced! The heart becomes weaker and tries to compensate. Spending years with a seriously weakened heart becomes a form of heart disease. Karen Carpenter's family understands this FACT all too well.

Dispelling a myth.... Truly amazing. We need better education and to teach critical thinking in our public schools, because not enough of our population can take Anatomy and Physiology in college.

Jovette - November 25, 2009 8:43 AM

I've heard that is not necessary to eat complementing plant-proteins if you are eating a variety of foods. Everything contains protein except for fruit. How could anyone possibly be deficient in protein? Eating a well balanced diet will provide your body with all the essential AA. And for this reason standard North American diets are way too high in protein and we could all use some non-animal proteins to limit the amount of 'bad' cholesterol and fat assosicated with eating animal protein which lead to CVD.

Unfortunately, I have not found any evidence, even in the articles referenced above, that there are plant products, other than Soy, that are complete proteins. I think the myth that needs to be busted is that meat protein is necessary with a well balanced diet to ensure that you are getting your RDI of protein. Would you be able to e-mail some Journals that contain information stating that plant proteins are not deficient in AA? I would love to show it to some of my dietary critics. I love your article by the way. Have your read: The China Study? It's a great book. Check it out:

William Keever - March 3, 2010 1:16 PM

Where is the proof that combining is a myth. Combining may not be necessary. It may not be necessary if a person is eating a normal amount of calories. THE QUESTION IS NOT WHETHER COMBINING IS NECESSARY BUT IF IT WORKS.

Dan - March 23, 2011 6:26 AM

The AHA gave a better reply after that, see

Circulation: Journal of the American Heart Association
Issue: Volume 106(20), 12 November 2002, p e148

Will - April 25, 2011 9:20 AM

But vitamin B12 is hard for vegans. that's where the algae, chorella, spirulina, etc. come in.

i don't care what anybody says. rice goes so well together w/ beans!

TruthDetector - May 30, 2011 5:42 PM

This article begins by identifying a myth, the myth of incomplete protein. No fact, evidence or rationale for this position is given. Labeling something a myth is a very poor approach to rhetoric. It is usually the last refuge for basis arguments. So, lets see some solid explanation for this position or simply retract you statements

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