Factors Affecting Energy Expenditure And The Efficiency Of Fuel Utilization: Feeding And Exercise Models

Abstract

The first aim of this dissertation was to monitor both rat and

human responses to short-term perturbations in energy balance

brought about through food energy restriction and refeeding,

exercise training and the cessation of exercise training or

surgical lipectomy. The second aim of this dissertation was

to identify factors which might explain differences in food

energy intake in weight-matched, weight-stable "large and

small eaters". The final aim of this dissertation was to

identify factors which might explain differences in resting

energy expenditure in a large sample of weight-stable men and

women, including exercising and non-exercising persons, and

including persons who may be regarded as "restrained eaters".

In the first study, Long-Evans rats underwent pre-weaning

litter size manipulation and were exposed to either a standard

chow diet or a diet comparatively high in fat during the

initial 18 weeks following weaning. Additionally, some of

the rats were housed as pairs, and others were housed singly

during the post-weaning period. Metabolic efficiency was

quantified by calculating feeding efficiency, changes in body

size, and body fat accretion. In this study, there was no

persistent effect of pre-weaning nutrition on post-weaning

growth and feeding efficiency.

In the second study of this dissertation, Long-Evans rats,

which were habituated to spontaneous running activity in

specially designed wheel cages trained for 8 weeks, after

which randomly-selected rats were placed in ordinary cages

without wheels for 2 weeks. The metabolic responses to shortterm

detraining were quantified by measuring feeding

efficiency, body mass, body fat accretion, and changes in

adipose tissue lipogenic enzyme activity in trained, detrained

and untrained rats. Rats which had stopped training

demonstrated an increased feeding effiency, a two- to threefold

increase in adipose tissue lipogenic activity, and

increased fat cell size and fat pad mass, when compared to

trained or sedentary counterparts.

The metabolic responses to stopping training were studied

further in human athletes. Resting and glucose-stimulated