Energy Expenditure under CR.

[Guest guest]

Hi folks:

This is interesting, imo. There is occasionally talk about the

supposed fact that when animals are put on CR the body redoubles its

efforts to conserve energy. This study's results suggest the

opposite is true. Which is rather surprising, to me.

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PMID: 15888333 // June 2005

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Key conclusion: " 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. "

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Full abstract:

" 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. "

Rodney.