Impact of Human Ageing on Energy & Protein Metabolism and Requirements
IDECG convened 27 scientists from 10 countries at the USDA Human Nutrition Research Center for the Ageing at Tufts University in Boston on 3-6 May 1999 to discuss the Impact of Human Ageing on Energy and Protein Metabolism and Requirements. Following are some of the main conclusions derived from the information presented at this workshop. An attempt was made to summarize what is known about major biological changes seen in elderly populations. Several of these changes seem to occur primarily as a result of the biological process of ageing (and can be referred to as primary), while others are frequently seen in elderly populations but seem to be more due to environmental and lifestyle factors (and can be referred to as secondary). There is evidence to suggest that several of the following changes are primary, have a biological basis, and are associated with the process of ageing in humans:
à a gradual loss in bone density with age that is accelerated in women after menopauseThe following age related changes have been observed although they may not be intrinsic to the process of ageing per se and may hence be considered as secondary. These changes may be caused by or influenced by extrinsic factors, which include the nature of the diet and level of physical activity as well as the lifestyle of the individual. (1) increased blood pressure; (2) reduced insulin action; (3) deranged fat metabolism; and (4) although strongly culturally influenced, there is a tendency for the aged to experience more social isolation and economic privation that can affect their health in multiple ways. While there are no specific data on elders, data from population studies, which include older persons, suggest that the following factors affect health and survival at any age but seem especially important for elders:
à sarcopenia (a loss of skeletal muscle), which may be slowed by resistance exercise
à a gradual reduction in basal metabolic rate (BMR) and total energy requirement as a consequence of sarcopenia and changes in organ size and function
à a gradual reduction in VO2 max and aerobic capacity
à loss of estrogens after menopause in women and a gradual decrease in androgens in men may contribute to sarcopenia
à although highly variable, there tends to be a gradual loss of acuity of taste and smell that may affect food intake
à a tendency to gastric atrophy which may result in a decreased absorption of vitamin B12
à cognitive impairment seen in the elderly is sensitive to vitamin and mineral status; reduced B vitamin and mineral status is known to adversely affect cognition in older persons.
à Aerobic and resistance exercise promotes health and contributes to a better quality of life for elders. Aerobic exercise slows age-related bone loss, improves balance, lowers lipids, reduces glycemia and risk of diabetes, and improves cardiovascular status. Strength training may stop or reverse sarcopenia, increase muscle strength and muscle mass in the elderly and can be the first step towards a lifetime of increased physical activity. Both forms of exercise are realistic strategies for maintaining functional status and independence.Recommendations and interventions should be based on these considerations.
à Increased vitamin D and dietary calcium intake may help slow the development of osteoporosis.
à Overweight and obesity predispose to co-morbidities including hypertension, heart disease, diabetes, osteoarthritis, and some cancers.
à Cessation of smoking improves health at any age.
à A diet with a relatively high variety of fruits and vegetables is highly beneficial.
à Diets relatively low in saturated fats reduce the risks of hypertension, coronary heart disease and some forms of cancer.
à The consumption of alcohol in moderation is compatible with sustained good health; however, it is better to abstain rather than to consume alcohol in excess.
à Although sensitivity to salt varies greatly within a population, salt intakes should be moderate; the higher the salt intake the greater the proportion of the population that will develop hypertension with an increased risk of cerebrovascular stroke.
à Improving the psycho-social environment of the elderly and alleviating economic privation will improve dietary intake and health maintenance.
à For elderly in nursing homes, physical and social activity, varied diets and assistance should be provided as required for mobility and eating.
à A major contributor to morbidity in the elderly are falls associated with poor balance and co-ordination that can be improved by activities that promote improved balance (e.g., Tai'chi, dancing, etc.).
Energy and protein requirements: The definition of energy requirements of the 1985 FAO/WHO/UNU Consultation as "the level of energy intake from food that will balance energy expenditure when the individual has a body size and composition, and level of physical activity consistent with long term good health" applies also to older people. Energy requirements are derived from estimates or measurements (with the doubly-labelled water method) of total energy expenditure (TEE), and most conveniently expressed as the Basal Metabolic Rate multiplied by a Physical Activity Level (PAL). One of the main problems is that the elders form a very heterogeneous group, some remaining healthy and very active, others becoming ill and/or very inactive. Most of the available data come from cross-sectional studies of elders in high-income countries. The PAL in reasonably healthy elders from such countries ranges from 1.5 to 1.8 with a mean of 1.65. The prevalence of many diseases increases with age. Many of these diseases limit the physical activity of patients, and even though the BMR may be slightly higher (e.g. because of an increase in body temperature), the net effect of disease is in general a lowering of TEE. The range of PAL becomes more variable, ranging from 1.1 to 1.6. In practical terms this means that in the ill. PAL may need to be determined on an individual rather than a group basis, taking also into account desirable body weight changes. Low energy intakes may endanger the adequacy of micronutrient intake, which may have to be monitored more closely.
Data on protein requirements are limited and suffer from methodological problems. Despite these limitations most currently available evidence suggests that, in healthy elders, a mean intake of 0.8 g of protein/kg bodyweight daily results in nitrogen balance. This is more than the current mean recommended intake of 0.6 g/kg/day. Information from nitrogen balance studies suggests that an even higher protein intake per kg bodyweight may be desirable for the elders. Even though further studies are needed before a recommendation to increase requirements can be made, it appears that protein intakes of 0.9-1.1 g/kg/day may be beneficial in healthy elders and are not harmful in the general population (i.e. in the absence of renal or hepatic disease).
Contact Beat Schurch, IDECG, PO Box 581, Lausanne, Switzerland; email firstname.lastname@example.org