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The Journal of Nutrition Vol. 129 No. 1 January 1999,
pp. 308S-310S
Department of Medicine, The University of Vermont, Burlington, Vermont 05405
Life expectancy at age 70 in the U.S. is 14 years longer than in most other industrialized nations. Unexplained weight loss and cachexia is a growing health problem and is one of the leading causes of death among the elderly population. Unexplained weight loss is a frequent clinical finding in elderly individuals and is often observed in apparently healthy individuals as well as in several disease states including, Alzheimer's disease, Parkinson's disease and congestive heart failure. For example, the National Institute of Neurological and Communicative Disorders and Strokes Task Force has included weight loss as a "clinical feature consistent with the diagnosis of Alzheimer's Disease". (Mckhann et al. 1984). Surprisingly little is known regarding the pathobiologic pathways leading to wasting in healthy or diseased elderly persons.
Weight loss is due to the mismatching of energy intake with energy expenditure. Energy dysregulation in older men and women leads to atrophy of muscle mass and accelerated loss of functional independence. The transition from vigor to frailty resulting from wasting increases the risks of decubitus ulcers, systemic infection, mortality and results in a greater consumption of health care resources (Pinchofsy and Kaminski 1986, Sandman et al. 1987 The specific charge of the Geriatric Discussion group was to address the following issues:
The following is a summary of the highlights of our group discussion:
Our first task was to define wasting. A working definition decided upon by the groups was: unintentional loss of body weight (5 to 10)% coupled with a functional impairment (body mass index < 28) in apparently healthy individuals.
A. Body Composition
INTRODUCTION
Introduction
References
). Despite the common clinical observations of weight loss in the elderly, the influence of these changes on health outcomes are as of yet unknown. In old age, episodic weight loss may occur in response to multiple chronic conditions. Age-related physiologic processes may limit the response to stress and accelerate change in body composition, leading to incomplete recovery from illness and a high probability of functional decline. The amelioration of nutritional problems related to wasting may prove to be one strategy for increasing quality of life, enhancing functional independence and possibly lessening the burden of a specific disease in the elderly population.
DEFINITION
ENDPOINTS
). Moreover, many of the techniques lack an accurate and valid criteria method to which other techniques can be compared. For example, studies have questioned the use of underwater weighing (together with the inherent assumptions of the Siri 2-compartment model) as a criteria method in the elderly because this approach does not account for possible heterogeneity in the density of fat-free mass. The derivation of fat-free mass from the measurement of total body water relies on the assumption that the hydration of fat-free mass is constant. Slight deviations from the assumed density values can result in large errors (Kehayias 1993). A rather new method for estimating body composition is dual-energy x-ray absorptiometry (DEXA) which, however, cannot as of yet be regarded as a "gold standard" (Roubenoff et al. 1993). The DEXA assumes a constant hydration factor of fat-free mass, which may be violated in older individuals. Moreover, there is increasing evidence that standard body composition assessment methods such as skinfold thickness and bioelectrical impedance analysis may not adequately estimate body composition in individuals over 65 years of age (Baumgartner et al. 1991, Deurenberg et al. 1990, Heymsfield et al. 1986). Recent developments in low radiation exposure measurement of body carbon and oxygen by neutron inelastic scattering and body protein by gamma ray resonance are possible examples of new technology that may provide more sophisticated measurements of the compartments of body composition (Kehayias 1993). It is becoming clear that improvements in body composition techniques are permitting a detailed examination of changes in the specific compartments of body composition and their impact on physiological function. The drawbacks of newer and more sophisticated methodologies are however, limited because of their availability, expense and complexity. This issue emphasizes the importance of age-dependent cross-calibration between widely used techniques (underwater weighing, DEXA, etc) with reference methods such as elemental partition analysis.
B. Energy Expenditure
Body weight is ultimately determined by the regulation of energy intake and energy expenditure. The unexplained loss of body weight suggests that low food intake, high levels of energy expenditure or a combination of both processes are contributing factors. The Discussion group agreed that accurate assessments of energy intake and energy expenditure would be useful in increasing our understanding of the pathophysiology of wasting in healthy and diseased elderly., Johnson et al. 1994). Moreover, it was noted that with increasing levels of adiposity, the degree of reporting bias increased (Johnson et al. 1994). Thus, although the assessment of food intake may provide a general or global estimate of caloric intake, its utility as a instrument to estimate individual energy needs is limited.
), congestive heart failure (Toth et al. 1997) and Alzheimer's disease (Poehlman et al. 1997). These initial findings suggest that problems of low energy intake, and not abnormally high levels of energy expenditure contribute to weight loss. Nonetheless, the capacity to measure total daily energy expenditure with doubly labeled water in free-living individuals in combination with measures of body composition can provide new information on the dynamic changes in energy output and its relation to loss body weight and composition in the cachectic elderly.
C. Functional Endpoints
Age-related decreases in body composition are least, in part, a cause for increased prevalence of disability in older adults. The Geriatric Discussion group suggested that both laboratory-based measures of function and practical (or field measures) of function be included in clinical trials examining the functional significance of wasting. Laboratory based measures are those tests that require specialized equipment and provide very precise assessments of function. Examples of these tests include: measurement of maximal or submaximal exercise capacity or assessments of muscular strength and size. Also deemed useful were other tests that assessed the ability to perform daily tasks such as carrying a bag of groceries, walking distance and velocity and specific tests of balance. The assessment of functional endpoints becomes useful given that recent studies have shown that particularly after strength conditioning, older women not only incease strength but also show improvements in walking velocity and the ability to carry out daily tasks such as rising from a chair and carrying a box of groceries (Hunter et al. 1995). Other endpoints considered by the Discussion group that are more related to disease outcomes included hospitalization time, survival endpoints, complication rates and wound healing.
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FOOTNOTES |
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LITERATURE CITED |
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Introduction
References
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