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Title: Relationships between exercise, energy balance, appetite and dietary restraint in overweight and obese women
Author: Brown, Gemma L.
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2012
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Background: Exercise may acutely and chronically up-regulate appetite and energy intake in overweight and obese women preventing body mass reduction in the long term. Overweight and obese women may be most prone to compensatory responses to exercise but the possible mechanism for this is unclear. Appetite regulating hormones have been investigated as a possible mechanism but to date the evidence is somewhat mixed. Identifying compensatory energy intake responses in overweight and obese women is complicated by the high prevalence of dietary under-reporting in this group. The laboratory-based buffet meal method has frequently been used in research studies that have assessed food intake in these women, but this method has only undergone preliminary validation. Dietary restraint may also affect individual appetite responses to exercise; it has been theorised that restraint may be a behavioural adaptation to diminished energy requirements, and differences in physical activity levels could also contribute. Evidence thus far has produced mixed results, possibly because two distinct sub-groups of restrained eaters exist, those with flexible and rigid control of restraint. It is not known if there are differences in energy requirements between these two sub-groups. Participants and Methods: Participants in all studies were sedentary, healthy, pre-menopausal, overweight and obese, adult women. Study 1: Fourteen women completed four trials; two exercise and two control, following the same protocol as study 1. Energy intake at three buffet meals and subjective appetite ratings were measured, and the reproducibility of these values under control and exercise conditions was tested using intraclass correlation coefficient (ri). Study 2: Twenty-nine women completed two trials in a randomised, counterbalanced order; exercise and control. Each trial lasted 24 hours spanning 2 days; the afternoon of day 1 and morning of day 2. An exercise session to expend 1.65 MJ was completed on day 1 of exercise trials, and three buffet meals were served during each trial to measure energy intake. Appetite was assessed using a visual analogue scale and blood samples were taken to determine acylated ghrelin (n=15) and peptide YY (n=10) concentrations. A repeated measures ANOVA was used to investigate the effects of trial and time on appetite hormones, EI and appetite. Study 3: Fifteen women participated in a sixteen week exercise intervention to expend 8360 kJ week-1. Participants exercised unsupervised in the University gym, and compliance was measured via heart rate monitoring. Sub-maximal fitness and body composition assessments were carried out at baseline, and after 8 and 16 weeks of exercise. Energy expenditure, energy intake, appetite, and acylated ghrelin (n=14) and peptide YY concentrations (n=11) were measured at baseline and after 8 weeks of exercise. Paired t tests were used to assess differences in time-averaged AUC for appetite, total and relative EI, metabolic rate, and exercise responses between trials. Repeated measures ANOVA was used to assess changes over time in body composition, appetite ratings, EI, acylated ghrelin, peptide YY, and cardiovascular fitness levels. Study 4: Forty-one sedentary women in a one week observational study. Participants were classed as restrained or unrestrained using the three factor eating questionnaire, and the former group were further classified as having flexible or rigid control of restraint. All participants completed a food frequency questionnaire, sub-maximal fitness test, body composition assessment and two fasted metabolic rate measurements. Average daily energy expenditure was calculated from a seven day physical activity diary combined with continuous heart rate data. Differences between restrained and unrestrained eaters, and restrained eaters with flexible and rigid control, were assessed using a paired t-test. Results Study 1: The ri for energy intake in control trials was significant but had large associated confidence intervals (ri 0.50 (95% CI 0.03, 0.80) p=0.0003). The ri was for energy intake in exercise trials was (ri 0.04 (95% CI -0.53, 0.55; p=0.45) and for the difference between control and exercise trials was (ri -0.05 (95% CI -0.54, 0.48; p=0.57) this was not significant. The ri values for satiety, fullness and desire to eat were significant in both control and exercise trials (p<0.05), but the associated confidence intervals were large. Study 2: There was no effect of exercise on subjectively rated appetite, acylated ghrelin, or peptide YY concentrations (all p>0.05). Total energy intakes were not significantly different between trials (exercise: 10.9 ± 0.5 MJ, control: 10.8 ± 0.5 MJ; mean ± SEM). Study 3: Total exercise energy expenditure during the intervention was 80.8 ± 7.7 MJ, which resulted in a significant reduction in total body mass (-1.9 ± 0.9 kg), fat mass (-1.7 ± 0.7 kg) and BMI (-0.7 ± 0.4 kg m-2). However individual changes in body and fat mass ranged from +2.8 to -9.9kg, and +1.78 to -6.55 kg respectively. There were no significant differences in appetite, energy intake, or expenditure after 8 weeks of exercise (p>0.05). Study 4: There were no differences in metabolic rate, daily energy expenditure or physical activity patterns between restrained and unrestrained eaters (p>0.05), or between restrained eaters with flexible and rigid control of restraint (p>0.05). Conclusions: Study 1: The laboratory-based buffet meal method of measuring energy intake does not provide reliable, reproducible values in overweight and obese, pre-menopausal women either under control or exercise conditions. Study 2: A walking-based exercise session which induces a moderate energy deficit of 1.65 MJ does not appear to affect subsequent twenty four hour energy intake, subjectively rated appetite, or plasma acylated ghrelin and peptide YY concentrations during the subsequent twenty four hours. Study 3: This study concluded that 16 weeks aerobic exercise in overweight and obese women produces a small, but significant, reduction in body and fat mass (-1.9 ± 0.9 kg); however the extent of these changes varies greatly between individuals (+2.8 to -9.9kg). No evidence of compensatory changes in energy intake or expenditure, subjective appetite ratings, or circulating levels of acylated ghrelin and peptide YY was apparent after 8 weeks of exercise. Study 4: This study concluded that there is no evidence of a difference in body composition or energy requirements between overweight and obese female restrained and unrestrained eaters, or between sub-groups of restrained eaters. Dietary restraint does not appear to be an adaptation to diminished energy requirements.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: RZ Other systems of medicine ; QP Physiology ; Q Science (General)