The Effect of Bed Rest on the Loss of Lean Muscle Mass

The Effect of Bed Rest on the Loss of Lean Muscle Mass

Sarcopenia is an age-related, insidious loss of lean muscle mass that is accelerated by physical inactivity and poor nutrition. Older adults are at increased risk of becoming physically incapacitated, so when they experience an acute event, such as pneumonia or a fracture, and are placed on bed rest, they lose muscle mass rapidly in addition to the normal aging process. However, extended bed rest and inactivity promotes loss of lean muscle mass regardless of age.

Dr. Paddon-Jones has been studying muscle metabolism and the effect of protein on muscle protein synthesis for a number of years. A study of healthy young adults with 28 days of bed rest found that they lost 2% of lean leg mass compared to healthy older adults who had 10% loss of lean leg mass in just 10 days. Even healthy, middle-aged adults had an 8% loss after 14 days. Older adults in the hospital had a 15% loss in just four days, which is a dramatic difference. This rapid loss of lean body mass in older adults is further compounded by the additional complications of hospitalization such as the decline in basal energy expenditure and reduced physical activity. Furthermore, it can lead to an increased risk of falls as well as increased morbidity and mortality.

Since dietary protein impacts muscle protein synthesis, the key is understanding what amount is beneficial and how protein should be distributed. Research on the ability of protein-rich foods to stimulate protein anabolism showed that a 4-ounce (oz) serving of meat (30 grams [g]) increased protein synthesis by 50% in both young and older adults. If exercise was added to the increased protein per meal, the result was a 100% increase in synthesis. Consuming 90 g of protein evenly over three meals provided a greater protein anabolic response then the typical pattern of eating 10 g at breakfast, 15 g at lunch, and 65 g in the evening. Based on a 75 kilogram (kg) adult, this equals 1.2 g/kg/day, which is above the current adult recommendation of 0.8 g/kg/day. Since we cannot store excess protein for later anabolism, the key is even distribution over 24 hours. Studies also indicate the ability for older adults to respond to a lower dose meal of 15 g per meal falls below the potential to build lean muscle mass. Once again, we need to advocate moving away from the tea-and-toast meal that is common when older adults live alone.

All healthy adults should focus on the concept of consuming a moderate amount of high-quality protein at each meal plus adding an exercise component to their daily plan, which can protect lean muscle mass over time. The registered dietitian nutritionist (RDN) can assist older adults in developing an individualized plan based on their energy requirements, activity level, and health status. The focus for adults experiencing short-term bed rest and injury is to aggressively implement a nutrition plan of 1.2 g of protein/kg/day (adjusted for body size) with the protein spread equally over

the day to reduce the rapid loss of muscle. Adding leucine in moderation to the meal plan has been effective to temporally protect muscle mass in hospitalized adults. Protecting lean muscle mass is just as important as protecting against rapid bone loss.

References and recommended reading

Kortebein P, Symons TB, Ferrando A, et al. Effect of 10 days of bed rest on skeletal muscle in health older adults. JAMA. 2007;297:1772-1774. doi:10.1001/jama.297.16.1772-b.

Mamerow MM, Mettler JA, English KL, et al. Dietary protein distribution positively influences 24-h muscle protein synthesis in healthy adults. J of Nutr . 2014;144(6):876-880. doi:10.3945/jn.113.185280.

Paddon-Jones D, Sheffield-Moore M, Zhang XJ, et al. Amino acid ingestion improves muscle protein synthesis in the young and elderly. Am J Physiol Endocrinol Metab . 2004;286(3):E321-8. http://www.ncbi.nlm.nih.gov/pubmed/14583440. Accessed May 18, 2016.

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