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The aim of the studies described in this thesis was to investigate the effects of the intensity of treadmill walking and training status on lipoprotein metabolism in the fasted and postprandial states in normolipidaemic individ uals. Twelve young (28±2 years) adults walked on the treadmill on two occasions, for 90 min at low intensity (30% maximal oxygen uptake, V02max) and moderate intensity (60% V02max) after an overnight fast. Venous blood samples were taken during, immediately, 1 and 24 hours after the end of each walk, all in the fasted state. Both exercise bouts reduced the serum triacylglycerol (TAG) concentrations 24 hours after exercise but these decreases were independent of the intensity of the previous exercise bout. In the light of the suggestion that the fasted state may not be a sensitive model to study the TAG metabolic capacity, the above experiment was repeated in young adults (n=12), with the two bouts of treadmill walking taking place 16 hours prior to the ingestion of a high fat meal 0.3 g fat·kg body weight·l , 67% energy from fat). In addition a third trial was introduced in which volunteers did not exercise prior to the ingestion of the meal (control trial). Venous samples were obtained in the fasted state and after the ingestion of the meal at hourly intervals for 6 hours. Moderate, but not low intensity, walking significantly attenuated (26%) the total lipaemic response to the meal compared with the control trial (5.51±0.5 mmoJ.l-l.h vs 7.40±0.7 mmol·J-l·h; p<0.05). However, the moderate intensity bout expended twice the energy expended during low intensity exercise as the two bouts were of similar duration (90 min). The third study, therefore, examined the effect of the intensity of walking on the lipaemic responses to a similar high fat meal in young adults (n=9), when the energy expenditure of the two walking bouts was held constant (90 min at 60% V02max vs 180 min at 30% V02max). In addition, expired air samples were collected before and after the meal in order to examine the metabolic responses to this meal. Both bouts of exercise attenuated to a similar degree (=30%) the total serum TAG response to the meal compared with the non-exercise trial (5.46±0.63 mmol·J-l·h and 5.53±0.58 mmol-l-l.h at low and moderate intensity respectively vs 8.09±1.09 mmol·J-l·h; p<0.05). Mean respiratory exchange ratio over 6 hours after the meal was lower (p<0.05) in both exercise trials than in the control trial indicating an enhanced fat oxidation during the observational period. All the above three studies were conducted in young adults. The aim of the last study was two-fold (i) to examine whether a bout of moderate intensity walking (60% V02max) would influence the lipaemic and metabolic responses to a fat meal in middle-aged women, as already shown for young adults and (ii) to test the hypothesis that this effect would be greater in trained individuals, by comparing these responses between a trained (n=9) and an untrained (n=13) group. Walking attenuated the total postprandial TAG response to the meal compared to the control trial in both trained (4.9±O.3 mmol·j-1·h vs 7.0±O.S mmol·j-1·h; p<O.OS) and untrained (7.0±O.8 mmol·j-1·h vs 8.4±O.8 mmol·P·h; p<O.OS) women groups. The TAG response to the meal was not significantly different between the two groups in the control trial but it was lower (p<O.OS) in the trained compared to the untrained group 16 hours after the exercise trial. In both groups walking enhanced fat oxidation and decreased fat storage during the postprandial period to a similar degree. The studies described in this thesis have shown that, in young adults and in middle-aged women, one prolonged bout of walking reduces the magnitude of postprandial lipaemia during the recovery period. This effect appears to be dependent on the energy expended during exercise, rather than on its intensity per se, and may be greater in the trained state.

The role of free radicals and antioxidants in human disease, particularly cardiovascular disease is an area of intensive research. Diabetes mellitus is the most common condition associated with increased oxidative stress and accelerated a therosclerosis.Increased levels of lipid peroxides and diminished antioxidant vitamin status have been reported in diabetic patients and are also implicated in the chronic complications of diabetes. The autoxidation and glycoxidation reactions of glucose are sources of free radicals in vitro and a preliminary investigation that these reactions may be a source of free radicals in vivo was undertaken in patients admitted to hospital with severe hyperglycaemia or diabetic ketoacidosis. Plasma lipid peroxides were elevated 2-7 fold above the reference range, but decreased during the recovery period in these patients. Plasma urate and ascorbate levels decreased rapidly, whilst interestingly, a-tocopherol levels / lipid ratios were preserved. The study indicated the resilient nature of the antioxidant defences in plasma, although further studies are required in order to elucidate fully the role of autoxidation and glycoxidation reactions in vivo. Insulin resistance and hyperinsulinaemia are also tightly linked with atherogenesisin type II diabetes and weight loss in obese subjects plays an important part in the reversal of insulin resistance. The safety and efficacy of two weight loss interventions - very low calorie diet (VLCD) and intensive conventional dietetic (ICD) therapy - on cardiovascular risk factors and indices of oxidative stress were investigated in obese diabetic and non-diabetic subjects. The ICD therapy produced modest weight loss in patients with established diabetes with transient improvements in diastolic blood pressure and plasma ascorbate, but with a reduction in vitamin E/ serum lipid ratios. The VLCD produced large and rapid weight loss in diabetic and non-diabetic patients with improvements in cardiovascular risk factors, lipid peroxides and vitamin E/ serum lipid ratios, which were maintained after 12 months. Plasma ascorbate concentrations were significantly lower in diabetic patients than nondiabetic patients on the VLCD, indicating that formulated diets may require higher concentrations of vitamin C for diabetic patients and this requires further investigation. The VLCD successfully reversed type II diabetes and normalized plasma lipid peroxide levels in two newly diagnosed patients.