Nutrition

NUTRITION

Adequate research plays a crucial role in preserving the health status and functional independence of older adults. Conversely, malnutrition is associated with an increased rate of morbidity, mortality, and a failure to thrive in the elderly population.

Factors affecting adequate nutrition in elderly individuals

There are a number of factors that manifest in older age that may adversely effect nutritional status and promote significant weight and muscle loss. This weight loss, or anorexia of aging, is associated with further deterioration in nutritional status, increased hospitalization and disease rates, and premature death.

Factors influencing nutritional status in elderly persons may be divided into three categories: psychological, social, and medical. For instance, psychological disorders such as depression and dementia are highly correlated with loss of body weight in nursing homes and are the major causes of weight loss in free-living elderly individuals. In addition, numerous studies have suggested that social isolation, low socioeconomic status, and poverty are also associated with reduced dietary intake and weight loss. Moreover, numerous medical factors such as the use of prescription medicines, poor dentition, institutionalization, a decrease in taste and smell sensations, and an inability to regulate food intake have all been suggested to decrease appetite and adversely affect nutritional status in older adults.

Challenges in assessing energy requirements

There are numerous problems that have hindered the establishment of nutritional recommendations in older adults. These problems are due, in part, to the reliance on measuring caloric intake to derive daily energy needs. Research has shown that when validated against newly developed techniques, the older methods used to assess caloric intake, such as self-recorded diaries, dietary interviews, and twenty-four-hour dietary recalls, consistently underestimate actual daily energy needs. In addition, the heterogeneity of the elderly population presents additional challenges. For instance, the current recommended daily allowances (RDAs) are suggested for individuals up to age fifty and to those over fifty-one years of age. However, this broad categorization of persons over fifty-one years does not take into consideration the numerous physiological differences and differing nutritional needs of individuals within this broad age group.

An alternative to assessing energy requirements by using energy intake methodologies is the utilization of daily energy expenditure, or the sum of calories burned throughout the course of a day. When an individual is weight stable, daily energy expenditure can be used as a proxy measure of daily energy needs.

Daily energy expenditure is comprised of three components: resting metabolic rate, the thermic effect of feeding, and the thermic effect of physical activity. Resting metabolic rate represents the greatest proportion of daily energy expenditure (60–75 percent), and is a measure of the energy required to sustain homeostasis and basic physiological functions. The thermic effect of feeding constitutes approximately 10 percent of daily energy expenditure and represents the energy cost of digesting, absorbing, storing, and metabolizing a meal. The most variable component of daily energy expenditure is the thermic effect of physical activity (15–50 percent), which includes the energy expended through both voluntary exercise and involuntary activities, such as shivering, fidgeting, and postural control. Research has suggested that age is associated with a decrease in all three of these components of daily energy expenditure.

A new and more accurate method to assess energy expenditure is the doubly labeled water technique, which was first validated for use in humans in the 1980s. This technique involves the oral administration of two isotopes of water (deuterium and oxygen-18), and is based on the fact that deuterium labeled water is lost from the body through the usual routes of water loss (urine, sweat, evaporation), whereas oxygen-18 labeled water is eliminated from the body not only as water, but also as carbon dioxide. Approximately one to three weeks following administration of the isotopes, urine samples are collected and analyzed to calculate carbon dioxide production, which is determined by the difference in the turnover rates of the two isotopes. Carbon dioxide production, in turn, is used to determine oxygen consumption, and hence energy expenditure.

The advantages of the doubly labeled water technique are: 1) it provides an accurate, noninvasive assessment of daily energy expenditure in the free-living environment; 2) measurements are performed over extended periods of time (two to three weeks), which helps account for the daily perturbations in energy expenditure; and 3) when used in combination with indirect calorimetry, it is possible to assess the thermic effect of physical activity. The disadvantages of the method lie mainly in its cost, which makes it impractical for widespread use in large-scale studies. Despite this limitation, however, doubly labeled water provides a more accurate measure of energy requirements than previous methods.

To support this claim, a 1996 summary of six studies utilizing doubly labeled water concluded that energy requirements in older individuals may be higher than the given recommendations. Other studies have also concluded that current recommendations underestimate energy needs of older, Caucasian men and women and African American men, but not African American women. These studies suggest that doubly labeled water may help us understand true energy needs and alleviate the various problems that have hindered the development of adequate nutritional recommendations for elderly persons. Furthermore, studies highlight the heterogeneity of the elderly population and the necessity to focus on the development of individual, rather than group, recommendations.

Summary and future considerations

Due to the pivotal role proper nutrition plays in preserving health, preventing morbidity and premature death in older adults, and the myriad of factors that can compromise nutritional status in older age, there is a critical need to provide well-founded recommendations for age-related changes in energy requirements. However, the heterogeneity of the aging population, along with the inaccuracy of traditional energy intake methods to assess energy requirements, have hindered the development of such recommendations.

The development of the doubly labeled water technique has enabled the accurate measurement of daily energy expenditure in free-living individuals. The majority of doubly labeled water studies have suggested that current recommendations may underestimate the actual energy needs of the elderly population. Despite the cost, long-term longitudinal studies utilizing this new method are needed to accurately assess the age-related changes in energy requirements.

Christopher L. Gentile Eric T. Poehlman

See also Congregate and Home-Delivered Meals; Malnutrition; Sarcopenia; Taste and Smell.

BIBLIOGRAPHY

Roberts, S. B. "Energy Requirements of Older Individuals." European Journal of Clinical Nutrition 50 (1996): S112–S118.

Starling, R. D., and Poehlman, E. T. "Assessment of Energy Requirements in Elderly Populations." European Journal of Clinical Nutrition 54 (2000): S104–S111.