Harvard Health Letter

By the way, doctor: Isn't quinoa a supplier of complete proteins?

Q. I read in your June 2010 issue that soybeans are the only plant food that could serve as a person's sole source of protein because they contain all eight essential amino acids. I thought quinoa does too.

A. Quinoa (KEEN-wah) is native to the Andes in South America. It's caught on lately in the United States as a healthful whole grain. Experts sometimes refer to quinoa as a "pseudocereal" because the Chenopodium quinoa plant it comes from is in the same botanical family as sugar beets and spinach, and not the grass family like wheat, rice, and the other grains we typically think of as being cereals.

There are eight essential amino acids (nine for children) — essential in the sense that they can't be synthesized by the body so they must be supplied by what we eat each day. Quinoa is a better source of these amino acids than many other grains. Most notably, it contains more lysine than wheat or rice does, and lysine is the amino acid most lacking in these two major sources of dietary protein for many people in the world. But the protein in soy contains substantially more lysine than the protein in quinoa, and by some standards, quinoa falls just short of the lysine needed to be classified as a complete provider of all eight essential amino acids.

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