Muscle Function and Protein

Original Editor - Lucinda hampton

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Protein Intake and Muscle Function in Older Adults[edit | edit source]

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Age-related loss of muscle mass and function increases the morbidity and mortality risk of age-related chronic diseases and increases the risk of disability. These concerns are going to become an even greater issue given the global increases in the aging population. The etiology of sarcopenia is complex and multifaceted and there is no widely available pharmacologic intervention with an appropriately low side-effect profile to directly combat this condition.

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Recent evidence shows that the recommended amounts of protein may be too low for elderly people.

  • Seniors may need 1.0-1.3 grams of protein for every kilogram of body weight. eg if you weight 82 kg this could mean consuming 80-104 grams of protein every day, regardless of your calorie intake.
  • The current protein RDA does not appear to meet the optimal protein requirements for older people to maintain skeletal muscle mass. Given that sarcopenia is, in part, underpinned by the reduced ability of dietary protein to stimulate muscle protein synthesis (MPS), increasing amounts of protein have been shown to result in better preservation of muscle mass.
  • As part of a multimodal intervention, increasing dietary protein intakes may support not only muscle mass maintenance but also bone health when calcium and vitamin D intakes are adequate.[1]

Why do older adults require more protein than younger individuals?[edit | edit source]

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The original RDA recommendations were made based on studies conducted in young healthy adults and do not take into account the many physiological changes that occur with aging. These recommendations were based on the concept of preventing deficiency as opposed to promoting optimal health, which may be of greater importance in the elderly.

  • There is mounting evidence that older adults need more dietary protein than their younger counterparts to support good health, promote recovery from illnesses, and maintain functionality.

The most common age-related causes of protein shortfall are inadequate intake of dietary protein (loss of appetite, gastrointestinal issues, reduced energy need, changes in food preference), a reduction in the utilization of available protein (anabolic resistance, insulin resistance, higher splanchnic extraction), and a higher basal requirement (acute and chronic diseases, inflammatory disease, increased oxidation of protein)[2]

  • Anabolic resistance is responsible, in part, for skeletal muscle atrophy with aging, muscle disuse, and during disease states. Anabolic resistance describes the reduced stimulation of muscle protein synthesis to a given dose of protein/amino acids and contributes to declines in skeletal muscle mass.[3]
  • Physical inactivity induces: anabolic resistance (that is likely exacerbated with aging), insulin resistance, systemic inflammation, decreased satellite cell content, and decreased capillary density[3].

Protein[edit | edit source]

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Proteins are essential nutrients for the human body. They are one of the building blocks of body tissue and can also serve as a fuel source. Protein is the only macronutrient that does not have an inactive compound to serve as a reservoir. Dietary amino acids must be incorporated into functional proteins[4].

  • Protein is a macronutrient that is essential to building muscle mass (there are three macronutrients: protein, fats and carbohydrates).
  • It is commonly found in animal products, though is also present in other sources, such as nuts and legumes.
  • Chemically, protein is composed of amino acids. Proteins are the building blocks of muscle mass

The nine amino acids that humans cannot produce on our own are called essential amino acids (EAAs). Essential amino acids are: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.

  • Protein foods that contain all essential amino acids are called complete proteins. They are also sometimes called ideal proteins or high-quality proteins. Complete proteins include fish, meat, dairy products, quinoa, hemp seeds, chia seeds and soy.
  • Many plant-based proteins are not complete proteins. These include beans, grains and legumes as well as vegetables, which contain small amounts of protein. Incomplete proteins can be combined to create complete proteins. Creating complete protein include eg. Beans and rice, peanut butter and whole grain bread, and macaroni and cheese[4]

Skeletal muscle contractile proteins are the largest protein reservoir and can be rapidly utilized to supply amino acids to the entire organism during fasting or stress. Insufficient protein intake to satisfy daily requirements leads to negative protein balance and results in skeletal muscle atrophy, impaired muscle growth, and functional decline. Therefore, it is important that the proper amount of protein is consumed to prevent muscle wasting and maintain skeletal muscle mass and function.[2]

Optimising Muscle Preservation[edit | edit source]

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Optimising nutritional intake through the introduction of protein-rich whole-foods, isolated proteins and nutrient compounds with purported pro-anabolic and anti-catabolic properties could offset impairments in muscle protein turnover and, ultimately, the degree of muscle atrophy.[5]The greatest effects are observed when resistance training and high protein diets are combined and appear to act synergistically.[6]

  • To get the best results exercise is needed: Older individuals should perform strength exercise using both heavy and light loads three times per week, ingest at least 1.2 g of protein/kg/day, evenly distribute their meals into protein boluses of 0.40 g/kg, and consume protein within 2 h of retiring for sleep[3]
  • Rapidly digested proteins that contain high proportions of essential amino acids (EAAs) and adequate leucine, are most effective in stimulating MPS. Protein intake should focus on whole food sources of protein that contain all of the EAAs (equired to stimulate MPS).[7] 

At every meal and snack try the over 65s should consider eg these diet ideas:

  • Swap out a starch or carbohydrate for a higher protein food eg smoked salmon; Cheese; Nuts (almonds, hazelnuts, mixed nuts, peanuts, peanut butter, sunflower seeds, walnuts); Seeds; Healthy meat jerky
  • Protein shakes. Protein shakes make a quick and easy protein breakfast. You can use a plant-based or animal-sourced form of protein. Some protein powders will even mix right into your coffee or tea. You want to make sure you use a high-quality protein powder that does not contain: Sugar; Salt; Additives. It's not clear if using supplements is superior to boosting protein in the diet[8].
  • Substitute meat for bread. Instead of going for a sandwich, make a meat roll-up. To make a quick lunch-to-go use a couple slices of thin turkey breast wrapped around salad.
  • Add Legumes, eggs, lean meats, fish, chicken, soy based products (tofu, tempeh); seaweed.
  • Increase Leucine intake. Leucine performs a number of functions in the body. It helps to regulate blood sugar, improves wound healing, and produces growth hormone. Leucine is best known for its role in the muscular system, including: Muscle Building. Scientists know that leucine is vital for muscle building and muscle repair. They aren't sure whether supplementing with leucine will build or repair muscles faster. According to the National Institutes of Health, Leuine supplements don't seem to increase endurance but may increase muscle mass when combined with strength training[8].

Conclusions[edit | edit source]

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Elderly adults are less responsive to the anabolic stimulus of low doses of amino acid intake compared to younger adults. However, this lack of responsiveness in elderly adults can be overcome with higher levels of protein consumption combined with appropriate exercise.

  • The lack of muscle responsiveness to lower doses of protein in older adults can be overcome with a higher level of protein intake.
  • The greatest effects are observed when resistance training and high protein diets are combined and appear to act synergistically.[6]
  • The requirement for a larger dose of protein to generate responses in elderly adults similar to the responses in younger adults provides the support for a beneficial effect of increased protein in elderly populations.
  • The consumption of high-quality proteins that are easily digestible and contain a high proportion of EAAs are the most beneficial.[9]

References[edit | edit source]

  1. Traylor DA, Gorissen SH, Phillips SM. Perspective: protein requirements and optimal intakes in aging: are we ready to recommend more than the recommended daily allowance?. Advances in Nutrition. 2018 May 1;9(3):171-82.Available from:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5952928/ (accessed 14.3.2021)
  2. 2.0 2.1 Deer RR, Volpi E. Protein intake and muscle function in older adults. Current opinion in clinical nutrition and metabolic care. 2015 May;18(3):248.Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4394186/(accessed 14.3.2021)
  3. 3.0 3.1 3.2 Morton RW, Traylor DA, Weijs PJ, Phillips SM. Defining anabolic resistance: implications for delivery of clinical care nutrition. Current opinion in critical care. 2018 Apr 1;24(2):124-30.Available from:https://pubmed.ncbi.nlm.nih.gov/29389741/ (last accessed 14.3.2021)
  4. 4.0 4.1 Live science What is protein. Available from: https://www.livescience.com/53044-protein.html(accessed 15.3.2021)
  5. Marshall RN, Smeuninx B, Morgan PT, Breen L. Nutritional strategies to offset disuse-induced skeletal muscle atrophy and anabolic resistance in older adults: From whole-foods to isolated ingredients. Nutrients. 2020 May;12(5):1533.Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7284346/ (accessed 14.3.2021)
  6. 6.0 6.1 Nutrition advance The 20 Highest Protein Foods Per 100 Grams Available from: https://www.nutritionadvance.com/highest-protein-foods-per-100-grams/ (accessed 10.3.2021)
  7. Jäger R, Kerksick CM, Campbell BI, Cribb PJ, Wells SD, Skwiat TM, Purpura M, Ziegenfuss TN, Ferrando AA, Arent SM, Smith-Ryan AE. International society of sports nutrition position stand: protein and exercise. Journal of the International Society of Sports Nutrition. 2017 Dec;14(1):1-25.Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5477153/ (accessed 15.3.2021)
  8. 8.0 8.1 Webmd Top Foods High in Leucine Available from: https://www.webmd.com/diet/foods-high-in-leucine#1 (last accessed 14.3.2021)
  9. Baum JI, Kim IY, Wolfe RR. Protein consumption and the elderly: what is the optimal level of intake?. Nutrients. 2016 Jun;8(6):359.Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4924200/(accessed 15.3.2021)