Effect of acute exercise and diet manipulations on postprandial metabolism in boys and girls

Elevated postprandial triacylglycerol concentrations ([TAG]) are associated with the development and progression of atherosclerosis, and are established as an independent risk factor for future cardiovascular disease. Considering the majority of the daytime is spent in a postprandial state typically, and the paediatric origins of atherosclerosis are well established, lifestyle interventions including manipulations of exercise energy expenditure and dietary energy intake should be initiated early in life. Therefore, this thesis aimed to investigate the postprandial metabolic responses to different exercise and energy intake manipulations in boys and girls, with concentrations of circulating TAG representing the primary outcome of interest. To achieve this, a total of 60 healthy 11 to 13 year old boys and girls were recruited into five experimental studies. The first experimental study (Chapter 4) demonstrated that a single session of high-intensity interval running (HIIR) involving 10 x 1 min intervals at 100% maximal aerobic speed (MAS) resulted in a moderate reduction in postprandial plasma [TAG] in 11 to 12 year old boys. In the second experimental study (Chapter 5), immediate replacement of the moderate-intensity exercise-induced energy deficit negated the reduction in postprandial plasma [TAG] in 11 to 13 year old boys. Furthermore, an exercise-induced energy deficit was required to promote an increase in whole-body fat oxidation. The importance of the associated energy deficit was explored further in Chapter 6, which demonstrated that a moderate-intensity exercise-induced energy deficit elicited a greater reduction in postprandial plasma [TAG] than an isoenergetic diet-induced energy deficit in 11 to 13 year old girls (21% vs. 10% respectively). Chapter 7 compared the effect of 10 x 1 min interval runs at 100% MAS (HIIR) and 5 x 1 min interval runs at 100% MAS combined with a mild reduction in habitual energy intake by 0.82 MJ (195 kcal; HIIR-ER) on postprandial metabolism in 11 to 13 year old girls. Acute manipulations of low volume HIIR and ER reduced postprandial plasma [TAG] and increased resting whole-body fat oxidation, with the magnitude of effect marginally, although not meaningfully, greater following HIIR than HIIR-ER. The final experimental chapter (Chapter 8) compared directly healthy 11 to 13 year old boys and girls postprandial TAG responses to acute HIIR. Although postprandial plasma [TAG] was substantially lower in boys compared with girls, the magnitude of reduction following HIIR was similar between the sexes (11% vs. 10% respectively). Collectively, these studies demonstrate the efficacy of acute moderate- and high-intensity exercise, and to a lesser extent energy-intake restriction, to reduce postprandial plasma [TAG] and increase resting whole-body fat oxidation in boys and girls. Furthermore, the beneficial effect of exercise on postprandial metabolism appears dependent on the maintenance of the associated energy deficit. These lifestyle interventions have the potential to provide a practical, effective and engaging stimulus to promote a healthier cardiovascular risk profile in early adolescence.