A Primer on Protein, Part 1
Today’s Dietitian
By Becky Dorner, RD, LD
Vol. 6 No. 4 p. 54

Dietetics professionals in long-term care often raise questions about protein: Can we provide enough for residents who eat poorly? How much is enough? How much is too much? Can we use protein to help heal wounds? How do we know our interventions work?

Protein Basics
Proteins account for approximately 17% of body weight, mostly in the form of lean tissue (muscle and connective tissue). Half of the body’s protein consists of collagen, actin, and myosin, which provide structure to the body, and hemoglobin, which transports oxygen to the cells.

Proteins perform many roles that are essential to life: growth and maintenance, fluid and electrolyte balance, acid-base regulation, blood clotting, enzymes, hormones, transportation, and antibodies.

Amino Acids
Every cell in the body contains protein. Proteins are made up of amino acids (AAs), often called the “building blocks” of protein. There are 20 AAs that make up all body proteins:
• Nine essential AAs (EAAs) — must be included in the diet because the body cannot synthesize them in sufficient amounts
• Eleven nonessential AAs — can be synthesized by the body in sufficient amounts
• Six of the nonessential AAs are also classified as semiessential — in certain conditions, these nonessential AAs become essential.

AAs bond together to form polypeptide chains that twist into complex protein shapes. There are an infinite number of formations depending on how AAs are combined. Proteins may be formed as strong rodlike shapes for structures such as tendons, or may have hollow formations to allow them to carry materials, such as hemoglobin carrying oxygen.

Protein Synthesis
The healthy adult body constantly turns over proteins, creating and degrading 250 to 300 grams of protein every day. Much of the protein comes from recycling AA. The body disassembles proteins from food and the body and reassembles them to make new proteins it needs to stay healthy. To achieve this, the body must have all the AAs it needs at the same time. If a specific AA is not readily available, the body will disassemble a protein or another AA and redesign it to make what it needs. If necessary, the body will break down its own proteins to obtain the needed AA.

Protein Digestion and Metabolism
Proteins in the foods we eat are not automatically ready to go to work. They must be broken down to supply the AAs the body needs to create its own proteins. Chewing grinds and moistens proteins in preparation for transport to the stomach, where hydrochloric acid denatures protein, unraveling the structure and allowing it to be further broken down into polypeptides and shorter AA chains. In the intestine, pancreatic and intestinal digestive enzymes divide these polypeptides into short peptide chains, tripeptides and dipeptides, and AAs, which are absorbed into the lumen of the small intestine, and any peptides are broken into AAs in the intestinal cells. AAs travel through the portal vein to the liver where they enter the bloodstream.

Protein Needs
For healthy adults, 0.8 grams of protein per kilogram of body weight per day is recommended. For older adults, 1 gram of protein per kilogram of body weight per day is recommended. However, needs increase for malnutrition, stress, or trauma. Pressure ulcers increase requirements to 1.2 to 2.0 grams per kilogram of body weight depending on the number and severity of pressure ulcers.

There is no way for the body to store extra AAs, so new sources of protein must be provided every day. If any of the EAAs are missing for protein synthesis, the remaining AAs are converted for use as energy, carbohydrate, or fat storage. For healthy adults, this is not usually a concern because the typical diet supplies an average of 50% of the total protein requirement in the form of EAA. Our bodies need only approximately 11% of the total protein requirement in the form of EAA.

Protein Sources and Quality
Animal proteins are considered the highest-quality proteins, as their composition resembles human tissue more closely than plant tissue. (The exception is gelatin, which is missing the EAA tryptophan). High-quality proteins, or complete proteins, contain sufficient amounts of all 9 EAAs. Plant proteins are considered incomplete or low-quality protein because they are either low in or missing one or more of the EAAs. Combining low- and high-quality proteins (complementary proteins) through a varied daily diet can achieve a healthy diet.

The purpose of quality measures is to assess whether sources of protein have the EAAs in the proportions needed by the human body. This is useful when trying to utilize a protein source that in and of itself will support protein synthesis (ideal for residents who are totally dependent on enteral or parenteral feedings). For adults who are consuming varied diets with multiple sources of protein, protein sources do not always have to be complete because the body will combine AA as needed to create the proteins it needs at any given time.

Thus, it is most important to concentrate on providing a diet that has a variety of foods and proteins with a balance of vitamins, minerals, and adequate energy sources.

— Becky Dorner, RD, LD, is a speaker and author who provides publications, presentations, and consulting services to enhance the quality of care for our nation’s older adults. Visit www.BeckyDorner.com for free articles, newsletters, and information, or call 800-342-0285.

References for this article are available upon request by e-mailing TDeditor@gvpub.com.

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