Re: Does CR really lower metabolism?

[Guest guest]

Hi folks:

Thinking about this issue LOGICALLY one might have expected that

evolution would have created a mechanism whereby, when calories are

in short supply, the body's tissues would economize on their use of

energy, in the interests of preventing, or at least delaying,

starvation. And similarly, for them to use energy more liberally

when it is freely available.

So, if these studies are accurate (and I have no reason to doubt

them) then it is further evidence of the risks associated with coming

to logical conclusions about things like this in the absence of

empirical evidence.

fwiw.

Rodney.

>

> In several studies and discussions, the idea that lower metabolism

> leads to longer lifespans has been called into question, as some of

> you may know already. It seems that CR does not lower energy

> expenditure to the degree (theoretically?)expected by cutting

certain

> given percentages of daily calories but there has been " the recent

> suggestion that under some circumstances (CR?)we might expect

> mitochondria to produce fewer free radicals when metabolism is

> higher--particularly when they are uncoupled " .

>

> 1: Mech Ageing Dev. 2005 Jun-Jul;126(6-7):783-93. Epub 2005 Mar 16.

> Related Articles, Links

>

> Energy expenditure of calorically restricted rats is higher than

> predicted from their altered body composition.

>

> Selman C, T, Staib JL, Duncan JS, Leeuwenburgh C,

> Speakman JR.

>

> University of Florida, Department of Aging and Geriatric

Research,

> College of Medicine, Gainesville, 32608, USA. c.selman@...

>

> Debate exists over the impact of caloric restriction (CR) on the

> level of energy expenditure. At the whole animal level, CR decreases

> metabolic rates but in parallel body mass also declines. The

question

> arises whether the reduction in metabolism is greater, smaller or

not

> different from the expectation based on body mass change alone.

> Answers to this question depend on how metabolic rate is normalized

> and it has recently been suggested that this issue can only be

> resolved through detailed morphological investigation. Added to this

> issue is the problem of how appropriate the resting energy

expenditure

> is to characterize metabolic events relating to aging phenomena. We

> measured the daily energy demands of young and old rats under ad

> libitum (AD) food intake or 40% CR, using the doubly labeled water

> (DLW) method and made detailed morphological examination of

> individuals, including 21 different body components. Whole body

energy

> demands of CR rats were lower than AD rats, but the extent of this

> difference was much less than expected from the degree of caloric

> restriction, consistent with other studies using the DLW method on

CR

> animals. Using multiple regression and multivariate data reduction

> methods we built two empirical predictive models of the association

> between daily energy demands and body composition using the ad lib

> animals. We then predicted the expected energy expenditures of the

CR

> animals based on their altered morphology and compared these

> predictions to the observed daily energy demands. Independent of how

> we constructed the prediction, young and old rats under CR expended

30

> and 50% more energy, respectively, than the prediction from their

> altered body composition. This effect is consistent with recent

> intra-specific observations of positive associations between energy

> metabolism and lifespan and theoretical ideas about mechanisms

> underpinning the relationship between oxygen consumption and

reactive

> oxygen species production in mitochondria.

>

> PMID: 15888333 [PubMed - indexed for MEDLINE]

>

>

>

> I'm sure the following has already been discussed here. I wonder how

> much light is shed upon its principal hypothesis as a result of the

> above abstract.

>

>

> 1: Aging Cell. 2004 Jun;3(3):87-95.

>

> Uncoupled and surviving: individual mice with high metabolism

have

> greater mitochondrial uncoupling and live longer.

>

> Speakman JR, Talbot DA, Selman C, Snart S, McLaren JS, Redman P,

> Krol E, DM, MS, Brand MD.

>

> Aberdeen Centre for Energy Regulation and Obesity (ACERO),

School

> of Biological Sciences, University of Aberdeen, Aberdeen, Scotland,

UK

> AB24 2TZ. j.Speakman@...

>

> Two theories of how energy metabolism should be associated with

> longevity, both mediated via free-radical production, make

completely

> contrary predictions. The 'rate of living-free-radical theory'

(Pearl,

> 1928; Harman, 1956; Sohal, 2002) suggests a negative association,

the

> 'uncoupling to survive' hypothesis (Brand, 2000) suggests the

> correlation should be positive. Existing empirical data on this

issue

> is contradictory and extremely confused (Rubner, 1908; Yan & Sohal,

> 2000; Ragland & Sohal, 1975; Daan et al., 1996; Wolf & Schmid-

Hempel,

> 1989]. We sought associations between longevity and individual

> variations in energy metabolism in a cohort of outbred mice. We

found

> a positive association between metabolic intensity (kJ daily food

> assimilation expressed as g/body mass) and lifespan, but no

> relationships of lifespan to body mass, fat mass or lean body mass.

> Mice in the upper quartile of metabolic intensities had greater

> resting oxygen consumption by 17% and lived 36% longer than mice in

> the lowest intensity quartile. Mitochondria isolated from the

skeletal

> muscle of mice in the upper quartile had higher proton conductance

> than mitochondria from mice from the lowest quartile. The higher

> conductance was caused by higher levels of endogenous activators of

> proton leak through the adenine nucleotide translocase and

uncoupling

> protein-3. Individuals with high metabolism were therefore more

> uncoupled, had greater resting and total daily energy expenditures

and

> survived longest - supporting the 'uncoupling to survive'

hypothesis.

> Copyright 2004 Blackwell Publishing Ltd.

>

> PMID: 15153176 [PubMed - indexed for MEDLINE]

>

>

>

[Guest guest]

>

> In several studies and discussions, the idea that lower metabolism

> leads to longer lifespans has been called into question, as some of

> you may know already. It seems that CR does not lower energy

> expenditure to the degree (theoretically?)expected by cutting

certain

> given percentages of daily calories but there has been " the recent

> suggestion that under some circumstances (CR?)we might expect

> mitochondria to produce fewer free radicals when metabolism is

> higher--particularly when they are uncoupled " .

[cut for length]

I have a possibly newbie-esqe question and observations. The studies

do not make any sense to me... Let's say that as a 'normal'

American, I eat 2500 kcal per day and maintain my weight. Whatever

my RMR is, I am still " using " that 2500 per day, one way or another.

Now, wouldn't you call 2500 my metabolic rate, based on that?

If I am CRing and am now eating 1500kcal per day and maintaining

weight, isn't 1500 my new metabolism, thereby meaning it is lower

than before?

My basic question is this - no matter how much you take in in kcal,

if you are maintaining your weight, can you call the number of kcal

you eat 'your metabolism'?

Thanks, and I hope I haven't confused the issue further.

in Albuquerque

[Guest guest]

> I have a possibly newbie-esqe question and observations. The

> studies

> do not make any sense to me... Let's say that as a 'normal'

> American, I eat 2500 kcal per day and maintain my weight. Whatever

> my RMR is, I am still " using " that 2500 per day, one way or another.

> Now, wouldn't you call 2500 my metabolic rate, based on that?

>

> If I am CRing and am now eating 1500kcal per day and maintaining

> weight, isn't 1500 my new metabolism, thereby meaning it is lower

> than before?

>

> My basic question is this - no matter how much you take in in kcal,

> if you are maintaining your weight, can you call the number of kcal

> you eat 'your metabolism'?

>

> Thanks, and I hope I haven't confused the issue further.

>

>

,

Calorie Restriction decreases Basal Metabolic Rate while overeating

increases it. My CR calculator web page has references to

several scientific papers on this issue:

http://www.scientificpsychic.com/health/cron1.html

Tony

[Guest guest]

Hi :

A couple of points. First, perhaps you already realize this, but

metabolic rate is not always equal to caloric intake. Someone who

had been consuming 2500 calories and whose weight had been stable,

who decided to start CRON by dropping their intake to 1500 (not

recommended here, dropping by 100 at a time would be far preferable)

would be consuming 1500 but would still have a metabolic rate equal

to 2500 initially. The metabolic rate would decline gradually until

body weight had dropped to the level at which the body's daily use of

energy was 1500 calories. During this intervening period the

difference would be made up by mobilizing fat reserves.

Second, the recent discussion about whether resting metabolic rate

rises or falls in CRON is not trying to address the issue of whether

total calories consumed at a lower weight, or even the total calories

expended at a lower weight, will be less. It is acknowledged that,

AEE, resting metabolic rate will be lower at a lower body weight.

Rather, instead, the discussion refers to the question of whether the

calories expended RELATIVE TO THE THE NEEDS, **PER UNIT**, FOR EACH

OF THE VARIOUS ACTIVE TISSUES, remains the same or rises or falls.

In a person who loses 25% of their weight, for example, their brain

will likely be using about the same number of calories. Their fat

reserves, being much smaller than they were will be using less, but

they never used much in the first place, so the decline there will

not be huge. The skin, organs, bones, muscles, blood etc. will all

be smaller to varying extents and so will use less calories at the

lower body weight.

But the interesting question is whether, given those reductions in

weight among all the various tissues, the resting caloric expenditure

is the same as one would expect given the reduced size of each of

these tissues, or less, or more.

The answer appears to be " more " . So it appears that, with a loss of

weight, the body does not economize on energy usage per unit of

tissue weight - if these studies are correct.

Rodney.

> I have a possibly newbie-esqe question and observations. The

studies

> do not make any sense to me... Let's say that as a 'normal'

> American, I eat 2500 kcal per day and maintain my weight. Whatever

> my RMR is, I am still " using " that 2500 per day, one way or

another.

> Now, wouldn't you call 2500 my metabolic rate, based on that?

>

> If I am CRing and am now eating 1500kcal per day and maintaining

> weight, isn't 1500 my new metabolism, thereby meaning it is lower

> than before?

>

> My basic question is this - no matter how much you take in in kcal,

> if you are maintaining your weight, can you call the number of kcal

> you eat 'your metabolism'?

>

> Thanks, and I hope I haven't confused the issue further.

>

>

> in Albuquerque

>