Posted by: Prospector PJ13 NOV 2008
There could be a good reason why determined gym users’ attempts to speed up their metabolic rate are such hard work and ultimately a waste of time. Recent research suggests that nature sets an optimum metabolic rate for all organisms, and the ones closest to this value are the best equipped for survival.
A study published in New Scientist appears to disprove the previously held theory that larger animals have a slower metabolism because they need to be more energy efficient. The study compared the metabolic rates of over 3,000 different species, ranging from bacteria to elephants.
It found that the average resting metabolic rate per unit mass varied by a factor of only 10,000, despite the fact that body mass varied by a factor of 1020.
The metabolic range for most species was even narrower, at 1–10W/kg, with no consistent relationship between metabolic rate and body mass. The smallest organism in the study, a bacterium, has a metabolic rate of 4W/kg, while an elephant ambles along at only 1W/kg. The previously held quarter-power scaling model predicted a multimillion-fold difference.
(Quarter-power scaling predicted that a range of biological variables could be determined by calculating body mass to the one-quarter power or to the minus one-quarter power. So an animal 100 times more massive than another would live about 100 to the quarter power, or three times longer than the other and heart rate would be a third as fast.)
It is unclear what evolutionary advantages an optimum metabolic rate might confer. The researchers suggest that the need to stay close to this value may help explain certain aspects of evolution, such as the size at which invertebrates needed to evolve a breathing mechanism, or the shape and size of tree leaves.
Metabolic rate is also one of the few biological functions that has been found to correlate with sleep patterns. Species with high metabolic rates for their size need less non-REM sleep. This suggests that animals with high metabolic rates sleep less because they burn more calories and so have to spend more time awake looking for food.
The attempts of Homo sapiens to confound these laws of nature by altering their lifestyle and taking drugs have not proved successful in the long term.