Re: Energy Expenditure under CR.

March 8, 2006

Back in 2004 (Message 14018), I brought up the topic that rodents on a

40%CR diet ate 18% more food per body weight than ad libitum controls

based on data by Mattson and Masoro. As these authors have found,

this 18% more food by weight translates to 30% to 50% more calories.

The fact that their model does not predict accurately means that they

don't have a good theoretical model.

Tony

>

> 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.

> =======================

> PMID: 15888333 // June 2005

> -----------------------

> 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. "

> -----------------------

> 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.

>

March 8, 2006