Article: Protein and Aging -- July 2008
July 1, 2008
The article, under the title “Protein & Aging,” was first published in the May, 2008 issue of Dietary Manager. For more information, see the end of this article. — Eds.
It is easy to appreciate the importance of protein in maintaining the health and quality of life of older adults, including their independence. A majority of our muscles and organs are made of protein. Muscle mass is critical for performance of the activities of daily living (ADLs), such as getting in and out of bed, eating, dressing, bathing and toileting. Further, maintenance of the protein content of certain tissues and organs, like skin, heart and liver, is essential for survival.
Although the recommended dietary allowance (RDA) is currently the same for all adults, 0.8g complete protein/kg body weight, there is considerable evidence that the protein requirement is probably greater for older adults. It is possible that the protein requirement for healthy older adults is as high as 1.0g or even 1.2g/kg body weight.
What Makes a Protein “High Quality”?Our body uses 20 amino acids to make body proteins. There is a dietary requirement for nine indispensable amino acids (also known as essential amino acids) that cannot be made by the body (see chart “Indispensable and Conditionally Indispensable Amino Acids in Protein”).
Sometimes, the dispensable amino acids, which can normally be made in sufficient quantities, must also be consumed in the diet, because the individual’s body is not making them fast enough due to disease or injury. When this is the case, these amino acids are called conditionally indispensable (a.k.a., conditionally essential amino acids).
Which Proteins Are High Quality?The Institute of Medicine recommends that the Protein Digestibility Corrected Amino Acid Score (PDCAAS) be used to evaluate how well a protein provides the human requirement for each indispensable amino acid.3 A single score is generated for each protein that indicates how well that protein provides all of the indispensable amino acids. A perfect score of 1.0 or 100% shows that the protein provides all of the indispensable amino acids at a level at or above the human requirement. If the score is less than 1.0 or 100%, one or more of the amino acids are deficient — compared to the requirement.
Using the amino acid composition data from the USDA Nutrient Database
The chart shows that almost all of the animal sources of protein previously taught as being “complete” proteins also have a PDCAAS percentage of 100. These provide all of the indispensable amino acids at levels at or above the human requirement.
The surprising exceptions to the perfect PDCAAS score are beef and some ground products, like sausage. As it turns out, beef and ground meat products can have a higher amount of connective tissue in them, which affects the protein quality. This connective tissue, which is mostly collagen, is comprised of protein, but it is completely missing the indispensable amino acid tryptophan. If there is a significant amount of collagen in a product, the product as a whole may be relatively deficient in the amino acid tryptophan, resulting in a PDCAAS of less than 100.
Use of PDCAAS in Menu PlanningOf course, well-written institutional menus have always included a variety of animal and vegetable sources of protein (e.g., dairy, egg, meat, beans, nuts, etc.). Across the menu, proteins of lesser quality are complemented by proteins of higher quality. It is the combined amino acid content of the meal, not the content of each individual food, which determines the amounts of indispensable amino acids available for protein synthesis. As long as the facility menu approximates the food group pattern of the USDA Food Guidance System (i.e., provides five to six servings from the meat/bean group and two to three servings from the dairy group), the menu will provide adequate amounts of overall protein and all of the indispensable amino acids.
Increasing Protein Intake in the Older Adult With a Poor AppetiteThe 80-100g protein and ~2,000 Kcal provided by most nursing home menus is adequate to meet the calorie and protein needs of most older adult residents who are eating well. However, these amounts may not be adequate for someone who has a wound or is recovering from surgery or an infection. Further, it is well-known that many residents consume less than 50% of their meals, on average. When residents do not eat enough food to maintain their weight, the protein they are consuming is being used by the body to provide calories instead of as a source of protein. For these residents, the facility will have to provide additional opportunities to consume foods that are high in calories and serve as additional sources of protein.
If energy and protein needs of an individual resident are not being met, a range of interventions can be implemented by the care team, including diet liberalization, honoring of food preferences, provision of additional assistance at meal time and snacks, liquid supplements, calorie- and protein-enhanced foods and drinks, and the addition of modular protein supplements. It is best to take a “food first” approach to nutrition intervention, as food enjoyment is an important aspect of the resident’s quality of life, and food is the best way to increase intakes of all the components that are likely to be deficient in a person who is not eating well: calories, protein, water and micronutrients.
If various approaches to increase food intake do not achieve desired improvements in protein status, liquid supplements and modular supplements are two types of commercial products that can be used to increase protein intakes. (The PDCAAS of the various proteins used in supplements is provided in the chart “PDCAAS of Protein Sources for Supplements.”) Most complete liquid supplements are made with casein and/or soy protein; these proteins have a PDCAAS of 100. Protein sources used in modular protein supplements (modular supplements are those that are not nutritionally complete) vary widely in their protein quality. In particular, the liquid collagen-based supplements have a wide range of PDCAAS scores. In general, it is best to offer a supplement with a PDCAAS of 100, so that the resident is sure to get enough of all of the indispensable amino acids as well as enough total protein.
Bottom LineOlder adults have high protein requirements which are not easily met if they have a small appetite. Therefore, it is the responsibility of dietary managers to assure that institutional menus provide a variety of high-quality sources of protein. When nutrition interventions are needed to increase the energy and protein intakes of an older adult, it is appropriate to first encourage intakes of high-calorie, high-protein foods and/or liquid supplements. If the protein needs of an older adult are still unmet, and it is determined that a modular protein supplement is needed, it is best to provide one with a PDCAAS of 100%.
This article was reprinted with permission from the Dietary Managers Association (DMA). DMA is a national, not-for-profit association established in 1960 that today has over 14,000 professionals dedicated to the mission of providing optimum nutritional care through foodservice management. For more information, see www.dmaonline.org.