Importance of skeletal muscle mass and function

Skeletal muscle accounts for 30–40 % of adult male and 20–30 % of female body size with losses of about 1 % per year starting after age 50 years⁽ Reference Mitchell, Williams and Atherton ^{4 )}. Muscle strength also declines with age and is associated with muscle loss. Muscle mass, strength and function are also correlated with each other leading to poor health outcomes and mortality⁽ Reference Malmstrom, Miller and Herning ^{5 ,} Reference Cruz-Jentoft, Landi and Schneider ^{6 )}. The loss of so much of this important body compartment with age leads to a number of conditions relating to public health and chronic health conditions as shown in Table 1 ⁽ Reference Hernlund, Svedbom and Ivergård ^{7 –} Reference Gale, Cooper and Sayer ^{9 )}.

Table 1. The impact of age-related skeletal muscle loss on conditions relating to public health and chronic health conditions

The mechanisms and causes for the loss of skeletal muscle mass strength and function with age were described during the meeting. The known causes of the loss of skeletal muscle mass are related to age, physical activity and smoking behaviours. However, other potential causes are under intensive research. The major research in nutrition has been in the type and amount of protein relevant for prevention and treatment of sarcopenia and cachexia. Although research indicates that there may be anabolic resistance to uptake of amino acids in older people, the current evidence suggests that sufficient dietary protein will overcome these issues⁽ Reference Murton ^{3 )}. Other aspects of diet may be relevant but have not been extensively studied⁽ Reference Welch ^{10 )}. Malnutrition is complex in its aetiology and treatment, and cannot always be corrected. The root causes may be clinical, social or economic. Clinically, it is likely to be due to poor appetite as a consequence of disease (physical or mental) and/or to the presence of disease that interferes with the utilisation of nutrients and, in cachexia increases metabolic rate. Malnutrition in the elderly can be due to a range of problems (physical ones such as poor hand grip, eyesight and teeth; underlying chronic diseases such as cancer; mental health issues (dementia, depression, etc.) and psycho-social issues such as loneliness). Problems often interact in a complex cycle which drives body weight and muscle mass down.

Skeletal muscle mass and malnutrition

Malnutrition can cause a wide range of adverse consequences as shown in Table 2. Compared with older people at low risk of malnutrition, those with medium to higher risk are estimated to consult a general practitioner about 60 % more, have over 30 % more outpatient visits and 82 % more inpatient visits. This estimate equates to a healthcare cost of more than £7·3 billion each year⁽ Reference Elia ^{11 )}. Thus there are clear physiological, social and economic interests in addressing skeletal muscle loss and malnutrition.

Table 2. The adverse consequences of malnutrition

Although the National Institute for Health and Clinical Excellence identified that oral nutritional supplementation reduced length of hospital stay by 1·4 d^{( 12 )} there remains uncertainty about the dietary and other interventions to effectively prevent malnutrition in community settings. Improving dietary intake and maintaining skeletal muscle mass and function are likely not only to have cost savings for the health and social care systems, but may also have benefit for the psychosocial aspects of an older person's life; with wider impact on morbidity.

Current messages for public health nutrition

Although research is ongoing, current messages for public health nutrition can follow the UK Government healthy eating advice which is pictorially represented in the eatwell plate (Fig. 1), depicting the proportions of four main food groups that should form the diet, namely: bread, rice, potatoes, pasta and other starchy foods; fruit and vegetables; milk and dairy foods; meat, fish, eggs, beans and other non-dairy sources of protein. Foods and drinks high in fat and/or sugar should be consumed in small amounts and infrequently. UK Government advice is based upon recommendations from the expert committees such as the Scientific Advisory Committee on Nutrition^{( 13 )}. Despite long-standing advice on the constituents of a healthier diet, many in the population fail to achieve these recommendations with consequent increased risk of diet-related morbidity and mortality.

Fig. 1. The eatwell plate. The UK national food model showing the proportions and types of foods that contribute to a balanced diet.

These recommendations underpin much public health guidance and catering standards in England, including the statutory school meal standards^{( 14 )}, Public Health England's Healthier and More Sustainable Catering Toolkit^{( 15 )} and recommendations from the Hospital Food Standards Panel^{( 16 )}. While underlying mechanisms and treatments for age-related muscle loss, sarcopenia, cachexia and malnutrition continue to be investigated, the key to prevention remains to encourage older people to achieve their energy and other dietary requirements in keeping with the Government's eatwell plate and associated messages relating to dietary supplements.

Public Health England's toolkits are based upon principles that meet the dietary reference values for population groups. For older people, Public Health England recognise that achieving appropriate energy levels does not necessarily mean choosing higher (saturated) fat and sugar foods given the wider diseases to which they contribute; although such foods may have a role in the short term to boost energy intake^{( 17 )}.