Exercise Energy Expenditure and Postprandial Lipemia in Girls

Keith Tolfrey; Alex Engstrom; Caoileann Murphy; Alice Thackray; Robert Weaver; Laura A. Barrett

Disclosures

Med Sci Sports Exerc. 2014;46(2):239-246. 

In This Article

Abstract and Introduction

Abstract

Purpose: This study aimed to examine the effect of 30 and 60 min of moderate-intensity treadmill walking on postprandial triacylglycerol concentrations ([TAG]) in healthy girls.

Methods: Eighteen 10- to 14-yr-old girls (mean ± SD; body mass = 48 ± 11 kg, body fat = 19.0 ± 4.6%, peak oxygen uptake [V̇O2] = 47 ± 6 mL·kg−1·min−1) completed three 2-d trials in a counterbalanced crossover design, each separated by 14 d. On day 1, they rested (CON) or completed 30 min (EX30) or 60 min (EX60) of intermittent treadmill exercise at 56% peak V̇O2, inducing energy expenditures of 777 and 1536 kJ (186 and 367 kcal), respectively. On day 2, after a 12-h fast, a capillary blood sample was taken for fasting [TAG] before a high-fat milkshake (80 kJ·kg−1 body mass) was consumed. Further blood samples were taken hourly over a 6-h postprandial rest period for [TAG]. ANOVA and Student's t-tests were used to analyze the data.

Results: Fasting [TAG] was lower in EX60 than CON (95% confidence interval [CI] = –0.36 to 0.04, effect size (ES) = 0.41) and EX30 (95% CI = –0.47 to 0.04, ES = 0.46); all group mean concentrations were low (≤0.90 mmol·L−1). The main effect for condition revealed differences in postprandial [TAG] over time (ES = 0.36). The EX60 total area under the [TAG] versus time curve was lower than CON (95% CI = –2.66 to –0.04, ES 0.40) and EX30 (95% CI = –2.11 to 0.15, ES = 0.30); CON and EX30 were similar (95% CI = –1.44 to 0.71, ES = 0.10).

Conclusion: This study demonstrates that 60 min but not 30 min of moderate treadmill exercise, with a gross energy expenditure of 1536 kJ (367 kcal), attenuated postprandial [TAG] in girls.

Introduction

Although the process of atherosclerosis is initiated during childhood, the clinical symptoms of athero sclerotic disease are not evident typically until adulthood.[25] Elevated plasma triacylglycerol concentrations ([TAG]) are associated with an increased risk of atherosclerosis.[38] The magnitude and duration of the rise in [TAG] in the postprandial period is positively related to the progression of atherosclerosis.[4] Furthermore, prospective cohort studies have demonstrated recently that nonfasting (postprandial) [TAG] independently predicts future cardiovascular events in men and women.[1,27] Indeed, accumulating evidence shows that postprandial [TAG] may better predict cardiovascular disease risk than traditional fasting measures.[1] Because most waking hours are postprandial, a combination of low physical activity and diets high in fat or carbohydrate may increase the risk of future cardiovascular disease with prolonged elevated [TAG].[28] Consequently, interventions that modulate postprandial lipemia by improving TAG metabolism should begin ideally during childhood and adolescence.[25]

Many studies have shown that acute aerobic exercise performed up to 18 h before a high fat meal attenuates postprandial [TAG] in adults, resulting typically in a 15%–25% reduction in the total area under the [TAG] versus time curve.[28] In contrast, only five studies that we are aware of have examined the influence of a single bout of moderate to vigorous-intensity exercise on postprandial [TAG] in adolescent boys.[2,21,30,34,36] In each of these studies, the postprandial TAG response was lower after exercise compared with a nonexercise control condition. Exercise-induced energy expenditure (EE) appears to reduce postprandial [TAG] in a dose-dependent manner in adults.[12,37] In contrast, this has not been shown in studies in boys.[34,36] In the most recent of these studies, both 30 and 60 min of intermittent treadmill exercise at 55% of peak V̇O2 were shown to be similarly efficacious at reducing mean postprandial [TAG] in 13-yr-old boys.[34] Although gross EE in the 60-min exercise condition (1967 kJ) was approximately double that for 30 min (982 kJ), the extra attenuation of postprandial [TAG] was only 4%, leading the authors to conclude a dose response was not evident.

Although accumulating evidence indicates that an exercise-induced reduction in postprandial [TAG] occurs in boys, it has not been possible to find any similar studies with girls. Studies have consistently demonstrated greater postprandial [TAG] in men than women,[7,16] which may reflect between sex differences in abdominal visceral adipose tissue, enhanced skeletal muscle clearance of circulating TAG and greater suppression of upper-body subcutaneous adipose tissue lipolysis in women.[7,15,18] Although the majority of exercise postprandial studies are with males, Gill et al.[13] compared 30 men and 43 women and reported that the exercise-induced attenuation in the postprandial TAG response was not different (23.5% vs 19.8%, respectively). However, it is not known whether exercise reduces postprandial [TAG] in girls, suggesting this is a serious gap in our understanding of this important marker of future atherogenic risk in young people.

International physical activity recommendations for children and adolescents generally range from 60 to 90 min·d−1.[8,17] Evidence suggests that girls are less likely than boys to meet these recommendations.[29] Furthermore, the decline in physical activity with age is more marked among young females.[26] Clearly, in order for exercise intervention strategies to be effective in the long term, the recommended exercise programs must be considered acceptable and sustainable by the target group. This highlights the need to identify the lowest dose of exercise EE that can reduce postprandial [TAG] in girls.

Therefore, the aim of this study was to examine the effect of 30 and 60 min of moderate-intensity exercise on postprandial [TAG] in healthy, but not endurance trained, girls for the first time.

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