What is An “Incomplete Protein?”

by Claire Harrison on March 30th, 2012


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For me, being happily gluten-free means eating many different kinds of foods—from meats to nuts—rather than just trying to replace bread products. This approach has sent me into the world of legumes, and I eat lots of beans. As a result, I’ve become more interested in the nutritional value of beans. More specifically, I began to wonder why beans are considered an “incomplete” protein.

I don’t know about you, but I’ve never really understood the term: incomplete protein. I know we have to “complete” the protein with other food, but what does that mean, and how are we supposed to do it?

Clearly, it was time to do some research, and here is what I learned.

There are 9 essential amino acids that come only from food.

Your body contains thousands of different proteins that have different metabolic functions. However, all proteins are molecules that include the same amino acids. It’s the arrangement of these amino acids that determines the type and function of a protein.

Your body can make many of these amino acids on its own, but not all. The nine essential amino acids that come from food and their main purposes are

  • Histidine—physical and mental growth
  • Isoleucine—muscle production, blood formation
  • Leucine—growth hormone production, tissue production and repair
  • Lysine—bone development, hormone production
  • Methionine—digestion of fats, removal of plaque
  • Phenylalanine—brain processes and mood
  • Threonine—monitoring of body proteins
  • Tryptophan—mood, pain, and sleep regulation
  • Valine—muscle production

 

    The proportion of these 9 essential amino acids in a food determines whether it is “complete” or “incomplete.”

    The “complete” or protein-rich foods: Certain foods contain the nine amino acids in a balanced ratio that enables your body to access them. Another way to put this: these foods deliver the protein to you immediately—in “one bite,” so to speak.

    Meat, poultry, fish, eggs, and dairy fall into this category as well as plant products made from quinoa and soy.

    The “incomplete” or less protein-rich foods: The plant-based foods—legumes, whole grains, nuts, seeds, fruits, and vegetables—also contain all the essential amino acids.

    However, they have a low amount in one or more of these acids. For example, lentils have a low amount of methionine, and brazil nuts have a low amount of lysine.

    This lower amount or “limiting amino acid(s)” creates an imbalance that limits the ability of the food to make its other amino acids available to you. To put it another way, you cannot get the protein in “one bite.”

    Your body creates a nutrition resource—an “amino acid pool”—from the food you eat during the day.

    Let’s say you eat rice cereal in the morning, salad at lunch, and legumes at dinner. Your body “pools” together the various essential amino acids from these foods and uses them, as needed, to create proteins.

    In other words, you do not have worry about creating the right balance of essential amino acids at any one meal. Your body handles the “balance-making” for you.

    The moral of the story: Eat a wide variety of non-processed, plant-based foods.

    Your body does the nutrition work for you, but you must give it the tools to get the job done.

    Highly processed foods, e.g., potato chips, and the “white” foods, e.g., white rice, are not good tools because they have been stripped of many good nutrients.

    To get the most efficient, effective use of the amino acids stored in your body, make sure your diet includes beans, whole-grain cereals and breads, sweet potatoes, brown rice, nuts and seeds, and fruits and vegetables.

    Helpful links for more information:

    • The Savvy Vegetarian: A good overview of this subject along with a helpful chart of complementary foods.
    • Self Nutrition Data: This website displays the amino acid proportions for individual foods.

     

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    Author Information: Claire Harrison, Ottawa, Canada

    By Claire Harrison: Claire writes The Food Refashionista blog about food and recipes for people who are gluten-sensitive, lactose-intolerant, and watching the weight for health reasons. (www.foodrefashionista.wordpress.com)

     


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