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

Acute effects of energy deficit induced by moderate-intensity exercise or energy-intake restriction on postprandial lipemia in healthy girls

Eleven healthy girls (mean ± SD: age 12.1 ± 0.6 years) completed three 2-day conditions in a counterbalanced, crossover design. On day 1, participants either walked at 60 (2)% peak oxygen uptake (energy deficit 1.55[0.20] MJ), restricted food energy intake (energy deficit 1.51[0.25] MJ) or rested. On day 2, capillary blood samples were taken at predetermined intervals throughout the 6.5 hr postprandial period before, and following, the ingestion of standardized breakfast and lunch meals. Fasting plasma triacylglycerol concentrations (TAG) was 29% and 13% lower than rest control in moderate-intensity exercise (effect size [ES] = 1.39, p = .01) and energy-intake restriction (ES = 0.57, p = .02) respectively; moderate intensity exercise was 19% lower than energy-intake restriction (ES = 0.82, p = .06). The moderate-intensity exercise total area under the TAG versus time curve was 21% and 13% lower than rest control (ES = 0.71, p = .004) and energy-intake restriction (ES = 0.39, p = .06) respectively; energy-intake restriction was marginally lower than rest control (–10%; ES = 0.32, p = .12). An exercise-induced energy deficit elicited a greater reduction in fasting plasma TAG with a trend for a larger attenuation in postprandial plasma TAG than an isoenergetic diet-induced energy deficit in healthy girls

Acute high-intensity interval running reduces postprandial lipemia in boys

INTRODUCTION: Acute moderate-intensity exercise reduces postprandial lipemia in boys. However, the effect of high-intensity exercise has not been investigated. This study examined the effect of low-volume, high-intensity interval running (HIIR) on postprandial plasma triacylglycerol concentrations [TAG]. METHODS: Fifteen healthy, active boys (means(SD): age 11.8(0.4) years; body mass 42.8(8.0) kg; peak oxygen uptake (V ̇2) 55(6) mL·kg·min) completed two, 2-day trials in a counter-balanced, cross-over design separated by 14 days. On day 1, participants rested (CON) or completed 10 x 1 min running intervals at 100% maximal aerobic speed, determined from an incremental peak V ̇2 test, with 1 min recovery between intervals (HIIR). On day 2, capillary blood samples were taken in the fasted state and at pre-determined intervals throughout the 6.5 h postprandial period while participants rested. A standardised breakfast was consumed at 08:00 immediately after the fasting sample and a standardised lunch meal at 12:00. RESULTS: Differences in fasting plasma [TAG] were small to moderate (95% confidence interval (95% CI) -0.11 to 0.01, Effect size (ES) = 0.40). Postprandial [TAG] was lower during HIIR compared with CON (95% CI -0.19 to -0.02, ES = 0.58). The total area under the [TAG] versus time curve was lower following HIIR compared with CON (5.2(1.1) vs. 5.8(1.5) mmol·L 6.5 h; 95% CI -1.18 to -0.12, ES = 0.50). CONCLUSIONS: This is the first study to show that low volume, high-intensity interval running attenuates postprandial [TAG] in healthy, active 11 to 12 year old boys

High-intensity running and energy restriction reduces postprandial lipemia in girls

PURPOSE: This study examined the potency of combining acute high-intensity exercise and energy-intake restriction on postprandial triacylglycerol concentrations ([TAG]) in healthy girls. METHODS: Sixteen 11- to 13-year-old girls (mean(SD): body mass 45.1(7.6) kg; peak oxygen uptake (V˙O2) 43(6) mL·kg·min) completed three, 2-day conditions in a counterbalanced, crossover design separated by 14 days. On day 1, participants completed 10×1 min interval runs (HIIR), 5×1 min interval runs combined with 0.82(0.19) MJ energy-intake restriction (HIIR-ER) or rested (CON). Exercise was completed at 100% maximal aerobic speed, determined from an incremental peak V˙O2 test, with 1 min recovery between intervals. On day 2, capillary blood samples were taken in the fasted state and at pre-determined intervals throughout the 6.5 h postprandial period. A standardised breakfast and lunch were consumed immediately and 4 h, respectively, after the fasting sample. RESULTS: Based on ratios of the geometric means (95% confidence intervals (CI) for ratios), fasting [TAG] was 16% and 8% lower than CON in HIIR (-24 to -7%, effect size (ES) = 0.49, P = 0.002) and HIIR-ER (-17 to 1%, ES = 0.24, P = 0.09) respectively; HIIR was 8% lower than HIIR-ER (-17 to 1%, ES = 0.25, P = 0.08). The total area under the [TAG] versus time curve was 10% and 9% lower than CON in HIIR (-16 to -3%, ES = 0.30, P = 0.01) and HIIR-ER (-15 to -2%, ES = 0.28, P = 0.01) respectively; HIIR-ER and HIIR were similar (-1%; -8 to 6%, P = 0.80). CONCLUSION: Manipulations of HIIR and ER reduce postprandial [TAG] in girls. The magnitude of effect was marginally, though not meaningfully, greater following HIIR than HIIR-ER

Sex differences in postprandial lipaemia after acute high-intensity interval running in young people

Acute exercise reduces postprandial triacylglycerol concentrations ([TAG]) in boys and girls; however, it is not known whether between-sex differences exist in response to exercise. Fifteen boys (mean(SD): 11.8(0.4) years) and sixteen girls (12.1(0.7) years) completed two, 2-day conditions. On day 1, participants rested (CON) or completed 10×1 min high-intensity interval runs at 100% maximal aerobic speed with 1 min recovery (HIIR). On day 2, participants consumed a standardised breakfast and lunch over a 6.5-h period during which seven capillary blood samples were collected. Based on ratios of the geometric means (95% CI for ratios), fasting [TAG] was 32% lower in boys than girls (-44 to -18%, ES=1.31, P<0.001), and 12% lower after HIIR than CON (-18 to -5%, ES=0.42, P=0.003); the magnitude of reduction was not significantly different between the sexes (8% (ES=0.36) vs. 15% (ES=0.47), respectively; P=0.29). The total area under the [TAG] versus time curve was 27% lower in boys than girls (-40 to -10%, ES=1.02, P=0.005), and 10% lower after HIIR than CON (-16 to -5%, ES=0.36, P=0.001); the magnitude of reduction was similar between the sexes (11% (ES=0.43) vs. 10% (ES=0.31), respectively; P=0.87). The small-moderate reduction in postprandial [TAG] after HIIR was similar between the sexes

Acute exercise and postprandial lipemia in young people

Exaggerated postprandial triacylglycerol concentrations ([TAG]) independently predict future cardiovascular events. Acute exercise and diet interventions attenuate postprandial [TAG] in adults. This paper aims to examine the exercise postprandial lipemia studies published to date in young people. Nine studies satisfied the inclusion criteria adopted for this summary. The majority of studies are in boys (22% girls) and have shown a single ~60 min session of moderate intensity exercise, performed 12 to 16 h before a standardised meal, reduces postprandial [TAG]. Manipulations of exercise duration and intensity suggest an exercise energy expenditure dose-dependent response is not supported directly in healthy young people. Studies investigating alternative exercise bouts have reported lower postprandial [TAG] after simulated intermittent games activity, high intensity interval running and cumulative 10-min blocks over several hours, which may appeal to the spontaneous physical activity habits of young people. Although extension of these initial findings is warranted, exercise may be an effective strategy to promote regular benefits in TAG metabolism in children and adolescents; this may contribute to an improved cardiovascular disease risk profile early in life

Role of physical activity in regulating appetite and body fat

Recent articles in the press have questioned the role of physical activity in regulating appetite and controlling bodyweight. These articles can be confusing and misleading for the public. Yet this is a complex area and there is disagreement about the importance of physical activity even among academics. Uncertainty and misunderstanding in this area may be related to the heterogeneity of the term ‘physical activity’ which encompasses sporting pursuits with extremely high levels of energy expenditure over prolonged periods of time, as well as everyday tasks involving much lower levels of energy expenditure on an intermittent basis. This latter form of physical activity includes what has been termed ‘non-exercise activity thermogenesis’ (NEAT). In the right circumstances, physical activity can make a major contribution to the maintenance of a healthy weight even in the absence of dietary control although a combination of the two is almost certain to be more effective. In the long-term, evidence suggests that for most people exercise is likely to lead to only modest weight loss. This may be due to an insufficient amount of physical activity being performed together with compensatory changes in eating and exercise behaviours. This is hard to prove because energy intake and energy expenditure are difficult to quantify in free-living situations. Individual differences in the way people respond to exercise due to both environmental (e.g. social class, education level, income, eating and exercise behaviours of family and peers, weather etc.) and genetic factors also contribute to uncertainty about the effectiveness of physical activity for weight control. Nevertheless, physical activity remains a vital component of a healthy lifestyle due to its positive influence on energy balance as well as its potential to reduce the risk of lifestyle-related diseases

Energy replacement diminishes the effect of exercise on postprandial lipemia in boys

Purpose: Acute bouts of exercise reduce postprandial triacylglycerol concentrations ([TAG]) in healthy boys and girls; however, it is not known whether this effect is mediated by the energy deficit. This study examined whether the exercise-induced reduction in postprandial [TAG] persists after immediate dietary replacement of the exercise energy expenditure (EE). Methods: Eighteen healthy 11- to 13-year-old boys (mean(SD): body mass 41.3(8.4) kg; peak oxygen uptake ( VO 2) 55(5) mL·kg-1·min-1) completed three, 2-day conditions in a within-measures, crossover design separated by 14 days. On day 1, participants rested (CON), exercised at 60% peak VO 2 inducing a net EE of 32 kJ·kg-1 body mass (EX-DEF) or completed the same exercise with the net EE replaced immediately (EX-REP). On day 2, capillary blood samples were taken in the fasted state and at pre-determined intervals throughout the 6.5 h postprandial period. A standardised breakfast and lunch meal were consumed immediately and 4 h, respectively, after the fasting sample. Results: Based on ratios of the geometric means (95% confidence intervals (CI) for ratios), EX-DEF fasting [TAG] was 19% and 15% lower than CON (-32 to -4%, ES = 1.15, P = 0.02) and EX-REP (-29 to 0%, ES = 0.91, P = 0.05) respectively; CON and EX-REP were similar (-4%; P = 0.59). The EX-DEF total area under the [TAG] versus time curve was 15% and 16% lower than CON (-27 to 0%, ES = 0.55, P = 0.05) and EX-REP (-29 to -2%, ES = 0.62, P = 0.03) respectively; CON and EX-REP were not different (2%; -13 to 20%, P = 0.80). Conclusion: Immediate replacement of the exercise-induced energy deficit negates the reduction in postprandial [TAG] in boys; this highlights the importance of maintaining a negative energy balance immediately post-exercise to maximise the metabolic health benefits of exercise

Metabolism and exercise during youth — The year that was 2017

Two publications were selected because they are excellent representations of studies examining different ends of the exercise-sedentary behavior continuum in young people. The first study is an acute response study with 13 mixed-sex, mid to late adolescents presenting complete data from 4 different randomized experimental crossover conditions for analyses. Continuous glucose monitoring showed that interrupting prolonged continuous sitting with body-weight resistance exercises reduced the postprandial glucose concentration compared with a time-matched uninterrupted period of sitting. Furthermore, the effects of the breaks in sitting time were independent of the energy content of the standardized meals, but variations in the area under the glucose time curves expression were important. The second study adopted a chronic 12-week exercise training intervention design with a large sample of obese children and adolescents who were allocated randomly to high-intensity interval training (HIIT), moderate-intensity continuous training, or nutritional advice groups. HIIT was the most efficacious for improving cardiorespiratory fitness compared with the other interventions; however, cardiometabolic biomarkers and visceral/subcutaneous adipose tissue did not change meaningfully in any group over the 12 weeks. Attrition rates from both HIIT and moderate-intensity continuous training groups reduce the validity of the exercise training comparison, yet this still provides a solid platform for future research comparisons using HIIT in young people