A link between metabolism and longevity was first proposed by Rubner (Rubner, 1883). From measurements on five different mammals (guinea pigs, cats, dogs, cattle, and horses), he observed that long-lived species are bigger and spend less energy per gram of tissue mass relative to short-lived species. The assumption of such link was rooted from the idea that animals have a limited supply of energy and the quicker they utilise it, the sooner they will die. This idea later became a principle of the rate of living theory (ROL, (Pearl, 1928). In line with this model, previous research on mice, and Glanville fritillary butterflies (Melitaea cinxia) revealed that individuals with higher metabolic rates, corrected for body mass, had a longer life span due to activation of uncoupling proteins(Niitepõld & Hanski, 2013; Wiersma et al., 2004). Similar findings were also reported in mice in which the activation of uncoupling proteins by both chemical and genetic approaches, caused higher metabolic rates and increased longevity (Caldeira da Silva et al , 2008; Keipert et al, 2011). Many other studies on different species have also shown that life span was positively correlated with resting metabolic rate or daily energy metabolism ((Lin et al., 2002; Oklejewicz & Daan, 2002; J R Speakman et al., 2003; Wiersma et al., 2004). However, other studies found no relationship between metabolism and longevity measured in voles ((Selman et al., 2008), blowflies Calliphora stygia ((Hulbert et al, 2004b), Drosophila melanogaster ((Hulbert et al. 2004a). Experiments where metabolism was manipulated by a cold exposure have failed to have impacts on both oxidative stress and longevity in short tailed field voles (Microtus agrestis) (Selman et al., 2008) and on longevity in mice (Vaanholt et al, 2008). Increased metabolism through exercise also had no effects on longevity in mice ((Vaanholt, et al, 2010). However, some other studies where energy expenditure has been manipulated have revealed a negative relationship between energy expenditure and life span (Daan, et al, 1996; Lemon & Barth, 1992), consistent with the predictions of the ROL theory. It has been demonstrated that most of the previous studies examining the link between metabolism and life span across species were performed using inappropriate statistical analysis, in which a correction for body size and phylogenetic independence effects were not applied (Furness & Speakman, 2008; Speakman, 2005).<br /> <br />The metabolic regulation of aging<br /> Witten by: <br />Assistant Professor Dr. Aqeel Handil Al Jothery (PhD UK, Physiology) Anaesthesia Techniques Department, College of Health and Medical Technologies, Al Mustaqbal University, Hilla, Iraq<br /><br />References,<br />Rubner, M. (1883). 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