Weight loss in human obesity
Hypothesis: The work examined the effect of rate and extent of WL on body composition, physiological function (e.g. respiratory function), psychological function (e.g. mood), appetite and behaviour. Methods: The PhD was designed as a series of structured, longitudinal studies examining specific physiological and psychological parameters, in the three groups of six healthy, but obese (BMI 30-35) men. Subjects were assigned to either a WL group: (1) total fast to achieve 5% WL in 6 days; (2) VLCD (2.5 MJ/d) to achieve 10% WL in 3 weeks; (3) LCD (5.0 MJ/d) to achieve 10% WL in 6 weeks. Results: The main findings of this thesis are, (i) There was little evidence of energy balance regulation in response to an acute total fast (36 h) in human subjects; (ii) Rate of WL is important in determining tissue loss. A slowest rate of WL (with LCD) induced the greatest loss of fat mass, relative to lean tissue. The VLCD only had a protein sparing effect, relative to fasting, after initial loss of LBM; (iii) Rate of WL had a pronounced effect on subjectively-rated fatigue. This, in turn, influenced physical activity and hence total daily energy expenditure. The faster the rate of weight loss, the more fatigued the subject felt. WL had no effect on muscle function nor central nervous fatigue; (iv) Fasting is a stressful means of weight loss leading to a negative mood, which was reversed upon re-feeding. Extent of WL positively influenced mood; (v) All groups cognitively restrained ad libitum intake, post weight loss. There was a negative correlation between increased restraint score and body weight maintenance (-0.519; p=0.027). Conclusion: Rate and extent of WL are both important in determining the success of WL in terms of tissue loss, health, well-being and quality of life. Starvation cannot be recommended as a means of WL. The most effective WL strategy, should be a LCD, conducted over a period of weeks, resulting in a slow rate of WL to maximise fat loss and health benefits.