Download Protein is essential for lean muscle growth and repair

Protein is essential for lean muscle growth and repair
A Fanning – September 2016
Over 20% of muscle is protein.
Many of us don’t give a second thought to muscle, believing it to be the domain of elite athletes interested in
peak physical performance. However adequate muscle is essential for everyday activity, and helps maintain
health throughout life (Deer and Volpi, 2015). Like bone, muscle mass unfortunately declines during later life
in a process called sarcopenia. Muscle makes up 30-40% of bodyweight in a healthy young person
(Janssen et al,. 2000) but from middle age this declines by 0.4 – 2.6% per year (Mitchell et al,. 2012),
increasing the risk of frailty, disability and physical dependence in older adults (Deer and Volpi, 2015).
Protein is a key nutrient for muscle mass. This is because muscle is largely comprised of a range of
proteins, from myosin and actin which are the major proteins that allow for muscle contraction, to other
proteins which allow for normal muscle metabolism.
Muscle is an adaptive tissue which can regenerate and respond to changes in its environment (Goldspink,
1998) by the constant turnover of the tissue that it is built from. This muscle protein turnover is driven by two
dominant forces - muscle protein breakdown, where old tissue is broken down, and muscle protein
synthesis, where new tissue is created. To support this turnover, our diet needs to provide the protein
building blocks for the body to create new muscle.
Healthy adults should consume at least 0.8g of protein per kilogram of bodyweight every day to
meet the minimum amino acid requirements for body tissue repair.
A number of factors determine how much protein is required. Global dietary protein recommendations are
defined as the lowest level of dietary protein intake that will balance the losses of nitrogen from the body,
and thus maintain the body protein mass, in persons at energy balance with modest levels of physical
activity (WHO/FAO/UNU, 2007). Typically this level is approximately 0.8g of protein per kilogram
bodyweight (Institute of Medicine, 2002; Commonwealth Department of Health and Ageing Australia, 2006;
EFSA, 2012). This recommendation would be around 68g and 54g per day for an 85kg man and 67kg
woman, respectively.
It is important to note that this level of protein is not developed to be the optimal intake of protein to maintain
health (WHO/FAO/UNU, 2007). In fact some countries provide acceptable distribution ranges for protein
where this minimum recommendation is at the bottom end of the recommended distribution (Institute of
Medicine) or even below the bottom end (Commonwealth Department of Health and Ageing Australia,
2006). While these ranges of protein, carbohydrate and fat intakes are required, recommended minimums
do not take into account the role played by other nutrients (Wolfe and Miller, 2008). Current acceptable
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ranges for dietary protein fall between 10-35% (Institute of Medicine) and 15-25% (Commonwealth
Department of Health and Ageing Australia, 2006) of energy intake.
Intakes of protein higher than the minimum recommendations are protective of muscle with ageing, where
1.2g per kilogram of bodyweight attenuated losses (Houston et al,. 2008). These data also match recent
guidance from medical and research groups which recommend 1-1.2g of protein per kilogram of bodyweight
per day for older adults (Bauer et al,. 2013; Deutz et al,. 2014).
The protective effect of protein is thought to be driven by a complex interaction of dietary protein providing
amino acids as a substrate to build and maintain new muscle. By delivering these amino acids, it also
provides a key anabolic signal to the muscle to synthesise new muscle (Groen et al,. 2015).
Consuming the required quantity of protein is crucial for rebuilding and toning muscle after
exercise.
The type of protein eaten can also impact the muscles’ response. Dairy protein is an excellent source of
high quality protein (Rutherfurd et al,. 2015) and is an excellent source to help support the growth and
maintenance of muscle. It contains high levels of the essential amino acids required by the body, and it is
also able to stimulate muscle protein synthesis to a greater extent than plant proteins, such as soy
(Wilkinson et al, 2007; Yang et al, 2012; Tang et al, 2009). When this protein source is combined with
resistance exercise, it leads to greater gains in muscle mass (Hartman et al, 2007; Volek et al, 2013).
This reinforces the requirement for high quality proteins in our diet and consolidates the view that protein
from dairy sources is an excellent product to meet protein and essential amino acid requirements, especially
for those interested in exercise, healthy lifestyles, and ageing well.
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References
1. Bauer, J., Biolo, G., Cederholm, T., Cesari, M., Cruz-Jentoft, A. J., Morley, J. E., … Boirie, Y. (2013). Evidence-based
recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group. Journal of
the American Medical Directors Association, 14(8), 542–59.
2. Commonwealth Department of Health and Ageing Australia, Ministry of Health New Zealand & National Health and Medical
Research Council (2006)
Nutrient Reference Values for Australia and New Zealand: Including Recommended Dietary Intakes. National Health and Medical
Research Council and The Ministry of Health, Canberra.
3. Deer, R. R., & Volpi, E. (2015). Protein intake and muscle function in older adults. Current Opinion in Clinical Nutrition and
Metabolic Care, 18(3), 248–253.
4. Deutz, N. E. P., Bauer, J. M., Barazzoni, R., Biolo, G., Boirie, Y., Bosy-Westphal, A., … Calder, P. C. (2014). Protein intake and
exercise for optimal muscle function with aging: Recommendations from the ESPEN Expert Group. Clinical Nutrition (Edinburgh,
Scotland), (April), 1–8.
5. EFSA Panel on Dietetic Products Nutrition and Allergies (NDA) (2012)
Scientific Opinion on Dietary Reference Values for protein. EFSA Journal, 10, 2557.
6. Groen, B. B. L., Horstman, A. M., Hamer, H. M., De Haan, M., Van Kranenburg, J., Bierau, J., … Van Loon, L. J. C. (2015). Postprandial protein handling: You are what you just ate. PLoS ONE, 10(11), 1–22.
7. Houston, D. K., Nicklas, B. J., Ding, J., Harris, T. B., Tylavsky, F. A., Newman, A. B., … Kritchevsky, S. B. (2008). Dietary protein
intake is associated with lean mass change in older, community-dwelling adults: the Health, Aging, and Body Composition (Health
ABC) Study. The American Journal of Clinical Nutrition, 87(1), 150–5.
8. Institute of Medicine. (2002) Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein,
and Amino Acid. National Academies Press, Washington DC.
9. Mitchell, W. K., Williams, J., Atherton, P., Larvin, M., Lund, J., & Narici, M. (2012). Sarcopenia, dynapenia, and the impact of
advancing age on human skeletal muscle size and strength; a quantitative review. Frontiers in Physiology, 3(July), 260.
10. Janssen, I., Heymsfield, S. B., Wang, Z., & Ross, R. (2000). Skeletal muscle mass and distribution in 468 men and women aged
18–88 yr. Journal of Applied Physiology, 89(1), 81–88.
11. Rutherfurd, S. M., Fanning, A. C., Miller, B. J., & Moughan, P. J. (2015). Protein digestibility-corrected amino Acid scores and
digestible indispensable amino Acid scores differentially describe protein quality in growing male rats. The Journal of Nutrition,
145(2), 372–9.
12. WHO/FAO/UNU (2007) Protein and amino acid requirements in Human Nutrition. Report of a Joint WHO/FAO/UNU Expert
Consultation. WHO, Geneva (Switzerland).
13. Wolfe, R. R., & Miller, S. L. (2008). The recommended dietary allowance of protein: a misunderstood concept. JAMA : The
Journal of the American Medical Association, 299(24), 2891–3.
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