The following is part two of a series from nutritionist Dipa Shah-Patel, MPH:
In my last article, I included a list of different foods and the grams of protein they contain. I also mentioned that although certain items appear to have similar amounts of protein, they differ in the composition of those proteins.
You may think of protein as a single nutrient, but it actually consists of building blocks called amino acids, each with a somewhat different structure. The human body uses about twenty amino acids to make body proteins. Eight of these are called “essential” amino acids because they cannot be produced by the adult body. They must be found in the foods that you eat. These eight essential amino acids are: isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. For children, histadine is also an essential amino acid, so they require a total of nine essential amino acids. Other amino acids are "nonessential", which means that your body makes them if you consume enough essential amino acids and enough calories during the day.
Some foods are considered to be “complete proteins.” A complete protein is a protein that contains all nine essential amino acids for the dietary needs of humans.1 In general, complete proteins can be found in animal foods, including meat, poultry, seafood, eggs and dairy. Some plant and microbial sources also contain complete proteins, including spirulina, quinoa, soy, buckwheat, hempseed, and amaranth.
Meals consisting of different foods can also provide essential amino acids. Wheat, rice, and corn have low amounts of lysine, while beans and lentils contain significant amounts, making beans and rice a complete protein. Other combinations include:
- beans and tortillas
- rotis (Indian bread) and lentils
- a peanut butter sandwich
- tofu with rice
- hummus with pita bread
Also, you do not need to eat foods containing all of the essential amino acids together at every meal. The myth of protein combining was widely accepted in the seventies largely due to the book “Diet for a Small Planet” by Frances Moore Lappe, but this was revised in a later edition. A 1997 position paper of the American Dietetic Association emphasized that because amino acids obtained from food can combine with amino acids made in the body, it is not necessary to combine protein foods at each meal. Adequate amounts of amino acids will be obtained if a varied diet containing unrefined grains, legumes, seeds, nuts and vegetables is eaten on a daily basis.2
Stay tuned for the next article, “Super Foods for Vegetarians!”
Dipa is available to answer any nutrition questions you may have. Email them to email@example.com.
1."Protein in diet". Medline Plus Medical Encyclopedia. (June 26th, 2008). U.S. National Library of Medicine and National Institute of Health, Retrieved on July 12th, 2008.
2. Meddina, VK, Burke, KI. Position of the American Dietetic Association: Vegetarian Diets (1997). J Am Diet Assoc. 1997;97:11.
Fürst P, Stehle P (2004). "What are the essential elements needed for the determination of amino acid requirements in humans?". J. Nutr. 134 (6 Suppl): 1558S–1565S.