Busting the Myth of the Complete Protein

Bag of potatoes on tabletop

Annie Spratt / Unsplash

Some of our many vegetarian readers probably learned this long ago, but I will admit to remaining a sucker regarding the myth of the "complete protein." So I am thinking maybe there are a lot of people with lingering fears of failing to combine the right vegetarian foods to make a "complete protein."

My path to enlightenment started with the story of magician and entertainer Penn Jillette's amazing weight loss. Success stories in dramatic weight loss maintenance are few and far between, so Jillette's accomplishment perks my interest. Many reports focus on the "potato diet" to which Jillette attributes his ability to break with his old ways. If you read the whole story, though, you see that he only stuck to a potato mono-diet for the first weeks before adopting a healthy diet rich in vegetables.

Surfing along this theme I learned that a mono-diet is a well-established method to "reset" tastes for salt and sugar as well as build a new relationship with food for sustenance rather than for entertainment, comfort, or pleasure. This led to the story of an Australian man who plans to eat only potatoes for a year (CAUTION: there are serious health risks from a potato-only diet, especially in cases of weak kidneys, so don't attempt this without the supervision of your doctor), as well as Dr. Walter Kempner's rice diet, in which rice is the only source of protein.

Let's be honest here: this is a pretty stupid way to diet and anyone out there desperately looking for a dietary solution to serious health problems should not try any crazy diets without excellent medical advice, because those health issues may be made worse by over-dosing on any single foodstuff.

But these crazy diets opened my eyes: how is it that doctors are saying a diet of all potatoes or all rice could be fine? Aren't those "incomplete proteins?"

Complete Protein Defined

So I dug a bit deeper. First, one has to understand what we mean by "complete protein." Proteins are made up of building blocks called amino acids. In order to grow a healthy body, you need many different kinds of amino acids - kind of like needing the lego blocks with two dots, four dots, and six dots before you can build anything real fun. Many of the building blocks can be made by our own bodies. But some cannot. These amino acids that we can only get into our bodies by eating are called "essential amino acids."

Also important: our bodies cannot store amino acids. Whatever we don't use gets eliminated. If we don't get enough in one day, our body loses some of its ability to maintain itself. (This is what makes "incomplete proteins" scary!)

Incomplete Protein Myth Explained

It turns out that potatoes and rice, and most every vegetable you can think of, do have all of the different amino acids. The myth of the incomplete protein got started from comparing the amounts of these essential amino acids in vegetarian sources with those in meats. In the vegetable sources, if you eat only the amount of the plant-based food necessary to get the minimum recommended dose of "total protein," you would come up short on specific amino acids.

But almost no one in the world eats only the amount of food that gives the minimum total protein. Eat a little bit more than the minimum and you get some extras of certain amino acids, but you get the minimum of all of the essential ones. If you still are not sure how this works, look at the math behind a simple example:

If an average size person should get at least 46.2 grams of protein, they would need to eat a bit more than 600 grams of rice. This would end up giving them only 88% of the daily recommended amount of one amino acid, lysine (which occurs in excess in beans, hence the famous beans-and-rice solution to the "complete protein" problem).

But here's the trick: there are approximately 130 Calories in 100 grams of rice. So the amount of rice needed to eat the minimum amount of total protein is less than 800 Calories of rice! If you eat closer to 700 grams of rice (still just over 900 Calories or under half of what even a sedentary adult needs), then you get a "complete protein" from the rice alone. Again, eating only rice all the time is not a good idea: even in Dr. Kempner's diet he had to add calories from fruits and sugar in order to avoid over-dosing his patients on some of the nutrients rice has in excess.

The point is that the foods we eat have way more proteins than we need, even the plant-based foods. The extra amino acids just pass through us and we get plenty of the amino acids essential to a healthy body. The myth of the incomplete protein is dead! That makes adopting a healthier and more sustainable lifestyle seem so much easier.