Human body composition : measurement and relationship with exercise, dietary intakes and cardiovascular risk factors
This thesis describes studies related to human body composition, concentrating upon methodology of measurement, and a study on the influence of brisk walking programme upon healthy, previously sedentary middle-aged men. In chapter I, the principles of the techniques used for measurement of body composition in this thesis are discussed. The limitations and potential sources of error associated with each are discussed. The response of body composition to exercise, and the relationship of this response to changes in cardiovascular risk factors are considered. General methods are described in chapter 2. Techniques suitable for measurement of body composition in "field" conditions are evaluated in chapters 3 and 4. Near infra-red interactance was found to under-estimate fatness, to an increasing extent with increasing fatness. Bio-electrical impedance estimates of body composition from different sets of prediction equations from the literature differed significantly. Most overestimated fatness, to an increasing extent with increasing fatness. In chapter 5 techniques for measurement of subcutaneous adipose tissue are evaluated by comparison with A-mode ultrasound. Skinfold thicknesses were better correlated with subcutaneous adipose tissue thickness than were interactance data. Chapters 6 and 7 describe a year-long study on the effects of a brisk walking programme on healthy, previously sedentary middle-aged men. Volunteers were randomly allocated to walking or control groups (n = 42 and 23 respectively). Brisk walking for on average 27 minutes per day was not found to influence body composition, although significant changes in lower limb skinfold thicknesses were observed. The relationship of changes in blood pressure and blood concentrations of total cholesterol, lipoprotein-cholesterol subfractions and triglycerides with changes in body composition and fat distribution is examined. Energy intake did not change during the study, despite the expected increase in energy expenditure, and lack of change in body composition. Changes in dietary cholesterol and fatty acid intakes during the year are described, and related to changes in cardiovascular risk factors. In conclusion, newer field techniques were not found to be a better predictor of body composition than skinfold thicknesses. Participation in the walking programme did not significantly influence body composition or energy intake.