Guy Hoelzer  wrote or quoted:
> Tim Tyler at tim{at}tt1lock.org

> > The best known and most effective intervention for extending the lifespan
> > of mammals (or practically anything else) is calorie restriction
- i.e. see:
> > 
> >   http://calorierestriction.org/
> > 
> > It doesn't work by changing the organism's metabolic rate - but rather by
> > activating adaptations for dealing with famine conditions - i.e. see:
> > 
> >   http://cr.timtyler.org/why/
> 
> I will have a look at this web site, but your claim seems illogical because
> the rate of calorie consumption is generally taken as a direct measure of
> metabolic rate.

Metabolic rate itself - in terms of raw energy consumption - is not a
very useful measure when comparing organisms of different size - since
it takes no account of body size.

A mouse has a much smaller body than an elephant - and while the
mouse burns far fewer calories, it is normally regarded as having
a metabolism that burns through them much faster than an elephant's
metabolism does.

There are various ways to adjust metabolic weight for body size.
In particular there is the notion of "specific metabolic rate".

This is desribed on:

  http://webusers.xula.edu/cdoumen/CAP/Metabolism3.html

Once you factor weight into the equation somehow (as you obviously
must if you want to claim any negative correlation between metabolic
rate and longvity) then it is no longer clear that dieting organisms
have reduced specific metabolic rates, since - while they burn energy
more slowly - they have fewer metabolically demanding tissues to support.

There are empirical studies of the issue - e.g.:

``Controlled trial of the metabolic effects of a very-low-calorie diet: 
  short- and long-term effects''

 - http://calorierestriction.org/pmid/?n=2407096

....shows an initial energy deficit - followed by weight loss and a 
recovery of the original specific metabolic rate.

There are several explanations of why this happens.

One is that the body of the dieting organism is pumped full of stress 
hormones, and it is thus encouraged into activity in the hope that 
activity will result in food.

Also - on a longer term basis - the non-restricted animals normally tend 
to become increasingly sleepy and sedentary - compared to the restricted
subjects - due to the onset of old age.

There's a nice 1:43 minute video of this on:
http://www.biomarkerinc.com/html/press.htm that provides a
dramatic demonstration of the effect.
-- 
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