Energy expenditure and aging

Abstract

The study of energy expenditure (EE) has deep roots in understanding aging and lifespan in all species. In humans, total EE decreases substantially in advanced age resulting from parallel changes in resting metabolic rate (RMR) and activity EE. For RMR, this reduction appears to be due to a reduction in organ mass and specific metabolic rates of individual tissues. However, these anatomical changes explain very little regarding the decline in activity EE, which is governed by both genetic and environmental sources. The biological control centers for activity EE are closely coupled with body mass fluctuations and seem to originate in the brain. Several candidate neuromodulators may be involved in the age-related reduction of activity EE that include: orexin, agouti-related proteins and dopaminergic pathways. Unfortunately, the existing body of research has primarily focused on how neuromodulators influence weight gain and only a few studies have been performed in aging models. Recent evidence suggests that activity EE has an important role in dictating lifespan and thus places emphasis on future research to uncover the underlying biological mechanisms. The study of EE continues to unlock clues to aging. IntroductionAmong the enormous literature on theoretical explanations of aging the role of energy expenditure (EE) has received the most attention. For thousands of years, energy expenditure and metabolism have provided an understanding of how we function today, tomorrow, and eventually when we cease to function altogether. The study of EE and aging has been spurred along by the intriguing association between high rates of EE in short-lived mammals and low rates of EE in long-lived mammals. Some propose that EE per lifespan is fixed and abundant usage will accelerate aging (Rubner, 1908). While many works have challenged and severely criticized the rate of living theory (Holloszy and Smith, 1986;Austad and Fischer, 1991), EE and the biological processes that control the machinery are very much under intense study (Speakman, 2005).Energy expenditure has often been purported as a cause of aging without a complete understanding of changes in each of EE components with age. A thorough understanding of the age-related changes in EE components will help reveal the potential compensatory strategies that preserve lifespan. For example, it remains unclear why EE due to physical activity declines across all mammalian phylogenetic lines. Although many hypotheses on aging have involved in some manner the rates of metabolism, the debate on the role of altering EE for enhancing lifespan continues with new data in humans (Manini et al., 2006). The results add new light to the role of EE in preserving average lifespan among older adults.Correspondence: Todd Manini, University of Florida, Institute on Aging, Department of Aging and Geriatric Research, 210 E Mowry Rd, PO Box 112610, Gainesville, FL 32611-2610, tmanini@aging.ufl.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted ...

The ActivityStat Hypothesis

“…However, it is likely that the activitystat setpoint may be flexible and dynamic; varying for example with season, age or energy intake. It is widely accepted that total energy expenditure [12] and moderate to vigorous physical activity [13][14][15] vary systematically with age and physical activity levels are higher in the warmer months and decline during the colder seasons [16] . Layered on top of this is a large intra-individual variability in daily physical activity levels of approximately 20% [2,17] .…”

Developmental stress has sex-specific effects on nestling growth and adult metabolic rates but no effect on adult body size or body composition in song sparrows

“…For example, individuals with higher metabolic rates have higher energy requirements and may have to spend more time foraging for food or be less likely to survive food shortages. High resting metabolic rates have also been linked to decreased longevity (Manini, 2010;Speakman, 2005). In addition, basal metabolic rates (BMRs) are positively correlated to reproduction, such that species with high BMRs often have higher reproductive rates (Hennemann, 1983).…”

Daily variability of resting energy expenditure in acute kidney injury patients on dialysis

“…[36][37][38][39] In addition, it has also been suggested that the appearance of these REE changes may depend on gender, adiposity, and lean body mass. 35,40 The study has some limitations. First, it was performed in a single center, and despite the substantial number of IC measurements, only 24 patients completed the five-day follow-up.…”