Body size and metabolism

Kleiber, Max

doi:10.3733/hilg.v06n11p315

Cited by 1,886 publications

(1,367 citation statements)

References 24 publications

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“…An increase in BMR with ageing is not only a real observation, but an ominous one. This observation is reminiscent of Kleiber's (1975Kleiber's ( ) (1932 pre-mortal rise in RQ seen in fasting animals. The conclusion that may be reasonably reached is that whilst BMR may decline slowly on a population basis there may be some populations and individuals that show negligible changes in BMR whilst others show an increase.…”

Section: Mechanisms Of Changes In Bmrmentioning

confidence: 52%

Mechanisms of changes in basal metabolism during ageing

Henry

2000

Eur J Clin Nutr

103

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A considerable number of physiological functions are known to show a gradual decline with increasing age. However, the effects of ageing differ widely between organ systems. It is believed that basal metabolic rate (BMR) falls dramatically with age. These observations, largely based on cross-sectional surveys, are discussed in light of our present understanding of the biology of ageing. This paper reviews both the longitudinal and crosssectional studies of BMR and presents evidence that the fall in BMR with ageing may be less dramatic than previously perceived. Indeed, some subjects may show an increase in BMR with ageing. The mechanism of changes in BMR during ageing will be discussed. Organ weight changes appear to have a profound impact on BMR. The use of BMR to predict total energy expenditure in the`old elderly' ( b 75 y) is unlikely to be of any practical use due to wide intra-and inter-individual variation in BMR. This wide intra-and inter-individual variation in BMR is due to illness, disease and other metabolic disorders seen in the elderly. Finally, the importance of measuring BMR in elderly populations for its use in clinical medicine will be discussed. Descriptors: aging; basal metabolic rate; body composition

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Section: Mechanisms Of Changes In Bmrmentioning

confidence: 52%

Mechanisms of changes in basal metabolism during ageing

Henry

2000

Eur J Clin Nutr

103

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“…It seemed to apply as much to ectotherms as to endotherms, undermining the theoretical basis of its derivation. By 1932, Kleiber 16 was already advocating an exponent of 0.72, which in the days before computers were widely available became 'rounded' to 3 4 or 0.75. In recent years, a body of theoretical work has become established, based on fractal geometry of O 2 supply networks, explaining why 0.75 would be expected to be the exponent for the scaling of metabolic rate.…”

Section: Comparison Of Energy Expenditure In Lean and Obese Animalsmentioning

confidence: 99%

Some mathematical and technical issues in the measurement and interpretation of open-circuit indirect calorimetry in small animals

et al. 2006

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Indirect calorimetry is increasingly used to investigate why compounds or genetic manipulations affect body weight or composition in small animals. This review introduces the principles of indirect (primarily open-circuit) calorimetry and explains some common misunderstandings. It is not widely understood that in open-circuit systems in which carbon dioxide (CO 2 ) is not removed from the air leaving the respiratory chamber, measurement of airflow out of the chamber and its oxygen (O 2 ) content paradoxically allows a more reliable estimate of energy expenditure (EE) than of O 2 consumption. If the CO 2 content of the exiting air is also measured, both O 2 consumption and CO 2 production, and hence respiratory quotient (RQ), can be calculated. Respiratory quotient coupled with nitrogen excretion allows the calculation of the relative combustion of the macronutrients only if measurements are over a period where interconversions of macronutrients that alter their pool sizes can be ignored. Changes in rates of O 2 consumption and CO 2 production are not instantly reflected in changes in the concentrations of O 2 and CO 2 in the air leaving the respiratory chamber. Consequently, unless air-flow is high and chamber size is small, or rates of change of O 2 and CO 2 concentrations are included in the calculations, maxima and minima are underestimated and will appear later than their real times. It is widely appreciated that bigger animals with more body tissue will expend more energy than smaller animals. A major issue is how to compare animals correcting for such differences in body size. Comparison of the EE or O 2 consumption per gram body weight of lean and obese animals is misleading because tissues vary in their energy requirements or in how they influence EE in other ways. Moreover, the contribution of fat to EE is lower than that of lean tissue. Use of metabolic mass for normalisation, based on interspecific scaling exponents (0.75 or 0.66), is similarly flawed. It is best to use analysis of covariance to determine the relationship of EE to body mass or fat-free mass within each group, and then test whether this relationship differs between groups.

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“…It includes, however, an extremely important feature, i.e. the fractal nature of the input power term, which is assumed, for all living organisms, to be proportional to their mass m to the power p=3/4 (Kleiber scaling law [9]). …”

Section: Introductionmentioning

confidence: 99%

Cancer metabolism and the dynamics of metastasis

Dattoli¹,

Guiot²,

Delsanto³

et al. 2009

Journal of Theoretical Biology

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Cancer growth dynamics, commonly simulated with a Gompertzian model, is analysed in the framework of a more recent and realistic model. In particular, we consider the setting of a tumor embedded in a host organ and investigate their interaction. We assume that, at least in some cases, tumor metastasis may be triggered by an 'energetic crisis', when the tumor exceeds the 'carrying capacity' of the host organ. As a consequence, dissemination of clusters of cancer cells is set in motion, with a statistical probability given by a Poisson distribution. The model, although still at a preclinical level, is fully quantitative and is applied, as an example, to the case of prostate cancer. The results confirm that, at least for the more aggressive cancers, metastasis starts very early during tumorigenesis and a quantitative link is found between the tumor's doubling time, its 'aggressiveness' and the metastatic potential.

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Body size and metabolism

Cited by 1,886 publications

References 24 publications

Mechanisms of changes in basal metabolism during ageing

Mechanisms of changes in basal metabolism during ageing

Some mathematical and technical issues in the measurement and interpretation of open-circuit indirect calorimetry in small animals

Cancer metabolism and the dynamics of metastasis

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