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Everywhere I read people talking about how to increase metabolism in order to improve weight loss and fitness. Be it with frequent meals, special foods, developing more muscular mass, etc. Overall people seem to have the idea that is one of the best goals for the human body.

No matter how naive it sounds, I can never stop comparing metabolism with a very old proverb:

'The flame that burns twice as bright burns half as long.' Lao Tzu

Is there any evidence on the effects of an increased metabolism on lifespan, health or wellbeing? Or just any known disadvantage?

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I would say that it does have the effect of lowering life span.

My main argument for that hypothesis is the fact that calorie restriction has been scientifically shown to increase the life span.

What happens when you are on calorie restriction?

  • Your metabolism lowers due to the lower intake of energy. The less you eat, the less energy the body has to waste, in the form of heat etc. (ncbi.nlm.nih.gov/pubmed/11113597). ( "FIRKO (fat insulin receptor knock-out) mouse, engineered so its fat cells lack the normal insulin receptors. The resulting animals dine on normal amounts of food, yet still grow up lean, resistant to diabetes and also live longer than usual, apparently because of altered mitochondrial metabolism." - Insulin is the main satiety hormone. With its action blocked, in just one cell population, longevity was achieved http://www.ellisonfoundation.org/research/metabolism-and-caloric-restriction).
  • Foods contain substances which cause oxidative stress to cells. Exercise also creates reactive oxides. Oxidative stress damages DNA and has a correlation with cancer, and an inverse correlation with longevity.
  • It also slows down almost all biochemical processes (aging processes as well) in the body, such as protein buildup in cells (eg. Alzheimers) (ncbi.nlm.nih.gov/pubmed/17183154). "The lifetime of mice can be extended simply by keeping them chilly. In other words, despite diet, if the animals’ core body temperature is kept slightly below normal, lifespan can be extended" - lowering temperature induces a lowering of metabolism. http://www.ellisonfoundation.org/research/metabolism-and-caloric-restriction)
  • By slowing down cellular biochemical processes, you also slow down the rate of their proliferation (cell division). By doing this you lower the risk of mutations during DNA replication, i.e. the risk of cancer is lower. The length of the chromosomal telomeres is also slower to shorten, which has been proven to be an excellent indicator of life span. (http://learn.genetics.utah.edu/content/begin/traits/telomeres/)

Our definitions of health and wellbeing are mutually exclusive of life span. That is, having a long life span doesnt necessitate wellbeing in the form of fitness. Exercising is highly stressful for the body. For an as long life span as possible, your best bet is to restrict calories and to have continuous low intensity physical activity (basically, try to stay as active when you are 80 as when you were 20, without the exercise part).

Arguments like these are very hard to follow up on, and it will take time before arguments like mine will be proven in humans, so this is purely speculative at the moment. They are however based on extensive knowledge and numerous scientific studies within the life sciences.

I would like to add a note on exercise. I mentioned that exercise induces oxidative stress. It indeed does, in small amounts. This is bad for the body in the acute phase, but in the long run the body becomes better adapted to dealing with those oxygen species; it increases enzymes and antioxidants, and as such helps protect the body from such stress. This is why continuous low intensity exercise, such as housework or walking, is better than an-hour-a-day high-intensity fitness training (en.wikipedia.org/wiki/Hormesis).

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This is all very, very speculative. Have you got any sources to back up these claims? –  Lego Stormtroopr Nov 2 '13 at 22:48
    
"FIRKO (fat insulin receptor knock-out) mouse, engineered so its fat cells lack the normal insulin receptors. The resulting animals dine on normal amounts of food, yet still grow up lean, resistant to diabetes and also live longer than usual, apparently because of altered mitochondrial metabolism." - Insulin is the main satiety hormone. With its action blocked, in just one cell population, longevity was achieved. –  Darko Sarovic Nov 3 '13 at 8:08
    
"the lifetime of mice can be extended simply by keeping them chilly. In other words, despite diet, if the animals’ core body temperature is kept slightly below normal, lifespan can be extended" - lowering temperature induces a lowering of metabolism. –  Darko Sarovic Nov 3 '13 at 8:08
    
These two comments come from ellisonfoundation.org/research/… –  Darko Sarovic Nov 3 '13 at 8:09
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Would you mind inserting those references into your answer? –  Lego Stormtroopr Nov 3 '13 at 22:11
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