A single bout of brisk walking increases basal very low-density lipoprotein triacylglycerol clearance in young men

Effectiveness of statins vs. exercise on reducing postprandial hypertriglyceridemia in dyslipidemic population: A systematic review and network meta-analysis

BACKGROUND

Individuals at risk of suffering cardiovascular disease (CVD) present with larger increases in blood triglyceride (TG) concentration after a high-fat meal than do healthy individuals. These postprandial hypertriglyceride levels are an independent risk factor for CVD. Prescription of statins and a bout of prolonged exercise are both effective in lowering postprandial hypertriglyceride levels. We aimed to evaluate the comparative effectiveness of statins vs. a bout of aerobic exercise in reducing fasting and postprandial TG (PPTG) concentrations in individuals at high risk of developing CVD.

METHODS

Thirty-seven studies from a systematic literature search of the PubMed, EMBASE, and Cochrane databases were included in this review. The selected studies conducted trials involving statin therapy (n = 20) or a bout of aerobic exercise (n = 19) and measured their impact on PPTG levels as the outcome. Two studies analyzed both treatments and were included in duplicate. The meta-analysis was constructed using a random-effects model to calculate the mean difference (MD). The Student t test was used to compare the data sets for statins vs. exercise.

RESULTS

Overall, statin and exercise interventions showed similar reductions in PPTG levels, with an MD of -0.65 mmol/L for statins (95% confidence interval (95%CI): -0.54 to -0.77; p < 0.001) and -0.46 mmol/L for exercise (95%CI: -0.21 to -0.71; p < 0.01). However, statins lowered fasting TG levels more than exercise (MD = -1.54 mmol/L, 95%CI: -2.25 to -0.83; p = 0.009).

CONCLUSION

Although aerobic exercise is effective in lowering blood TG levels, statins seem to be more efficient, especially in the fasted state. A combination of exercise and statins might reveal a valuable approach to the treatment and prevention of CVD. More studies are required to determine the underlying mechanisms and the possible additive effects of these interventions.

Impaired repletion of intramyocellular lipids in patients with growth hormone deficiency after a bout of aerobic exercise

BACKGROUND

Ectopic lipids such as intramyocellular lipids (IMCL) are depleted by exercise and repleted by diet, whereas intrahepatocellular lipids (IHCL) are increased immediately after exercise. So far, it is unclear how ectopic lipids behave 24 h after exercise and whether the lack of growth hormone (GH) significantly affects ectopic lipids 24 h after exercise.

METHODS

Seven male patients with growth hormone deficiency (GHD) and seven sedentary male control subjects (CS) were included. VO_2max was assessed by spiroergometry; visceral and subcutaneous fat by whole body MRI. ¹H-MR-spectroscopy was performed in M. vastus intermedius and in the liver before and after 2 h of exercise at 50% VO_2max and 24 h thereafter, while diet and physical activity were standardized.

RESULTS

Sedentary male subjects (7 GHD, 7 CS) were recruited. Age, BMI, waist circumference, visceral and subcutaneous fat mass was not significantly different between GHD and CS. VO_2max was significantly lower in GHD vs. CS. IMCL were diminished through aerobic exercise in both groups: (-11.5 ± 21.9% in CS; -8.9% ±19.1% in GHD) and restored after 24 h in CS (-5.5 ± 26.6% compared to baseline) but not in GHD (-17.9 ± 15.3%). IHCL increased immediately after exercise and decreased to baseline within 24 h.

CONCLUSION

These findings suggest that GHD may affect repletion of IMCL 24 h after aerobic exercise.

The Influence of Pre-Exercise Glucose versus Fructose Ingestion on Subsequent Postprandial Lipemia

Ingestion of low glycemic index (LGI) carbohydrate (CHO) before exercise induced less insulin response and higher fat oxidation than that of high GI (HGI) CHO during subsequent exercise. However, the effect on the subsequent postprandial lipid profile is still unclear. Therefore, the aim of this study was to investigate ingestion of CHO drinks with different GI using fructose and glucose before endurance exercise on the subsequent postprandial lipid profile. Eight healthy active males completed two experimental trials in randomized double-blind cross-over design. All participants ingested 500 mL CHO (75 g) solution either fructose (F) or glucose (G) before running on the treadmill at 60% VO₂max for 1 h. Participants were asked to take an oral fat tolerance test (OFTT) immediately after the exercise. Blood samples were obtained for plasma and serum analysis. The F trial was significantly lower than the G trial in TG total area under the curve (AUC; 9.97 ± 3.64 vs. 10.91 ± 3.56 mmol × 6 h/L; p = 0.033) and incremental AUC (6.57 ± 2.46 vs. 7.14 ± 2.64 mmol/L × 6 h, p = 0.004). The current data suggested that a pre-exercise fructose drink showed a lower postprandial lipemia than a glucose drink after the subsequent high-fat meal.

The Ability of Exercise-Associated Oxidative Stress to Trigger Redox-Sensitive Signalling Responses

In this review, we discuss exercise as an oxidative stressor, and elucidate the mechanisms and downstream consequences of exercise-induced oxidative stress. Reactive oxygen species (ROS) are generated in the mitochondria of contracting skeletal myocytes; also, their diffusion across the myocyte membrane allows their transport to neighbouring muscle tissue and to other regions of the body. Although very intense exercise can induce oxidative damage within myocytes, the magnitudes of moderate-intensity exercise-associated increases in ROS are quite modest (~two-fold increases in intracellular and extracellular ROS concentrations during exercise), and so the effects of such increases are likely to involve redox-sensitive signalling effects rather than oxidative damage. Therefore, the responses of muscle and non-muscle cells to exercise-associated redox-sensitive signalling effects will be reviewed; for example, transcription factors such as Peroxisome Proliferator Activated Receptor-gamma (PPARγ) and Liver X-Receptor-alpha (LXRα) comprise redox-activable signalling systems, and we and others have reported exercise-associated modulation of PPARγ and/or LXRα-regulated genes in skeletal myocyte and in non-muscle cell-types such as monocyte-macrophages. Finally, the consequences of such responses in the context of management of chronic inflammatory conditions, and also their implications for the design of exercise training programmes (particularly the use of dietary antioxidants alongside exercise), will be discussed.

Weekday variation in triglyceride concentrations in 1.8 million blood samples

Triglyceride (TG) concentration is used as a marker of cardiometabolic risk. However, diurnal and possibly weekday variation exists in TG concentrations. The objective of this work was to investigate weekday variation in TG concentrations among 1.8 million blood samples drawn between 2008 and 2015 from patients in the Capital region of Denmark. Plasma TG was extracted from a central clinical laboratory information system. Weekday variation was investigated by means of linear mixed models. In addition to the profound diurnal variation, the TG concentration was 4.5% lower on Fridays compared with Mondays (P < 0.0001). The variation persisted after multiple adjustments for confounders and was consistent across all sensitivity analyses. Out-patients and in-patients, respectively, had 5.0% and 1.9% lower TG concentrations on Fridays compared with Mondays (both P < 0.0001). The highest weekday variations in TG concentrations were recorded for out-patients between the ages of 9 and 26 years, with up to 20% higher values on Mondays compared with Fridays (all P < 0.05). In conclusion, TG concentrations were highest after the weekend and gradually declined during the week. We suggest that unhealthy food intake and reduced physical activity during the weekend increase TG concentrations which track into the week. This weekday variation may carry implications for public health and future research practice.

Intensity-dependent and sex-specific alterations in hepatic triglyceride metabolism in mice following acute exercise

Precise regulation of hepatic triglyceride (TG) metabolism and secretion is critical for health, and exercise could play a significant role. We compared one session of high-intensity interval exercise (HIIE) vs. continuous exercise (CE) on hepatic TG metabolism. Female and male mice were assigned to CE, HIIE, or sedentary control (CON). HIIE was a 30-min session of 30-s running intervals (30 m/min) interspersed with 60-s walking periods (5 m/min). CE was a distance- and duration-matched run at 13.8 m/min. Hepatic content of TG and TG secretion rates, as well as expression of relevant genes/proteins, were measured at 3 h (day 1) and 28 h (day 2) postexercise. On day 1, hepatic [TG] in CE and HIIE were both elevated vs. CON in both sexes with an approximately twofold greater elevation in HIIE vs. CE in females. In both sexes, hepatic perilipin 2 (PLIN2) protein on day 1 was increased significantly by both exercise types with a significantly greater increase with HIIE than CE, whereas the increase in mRNA reached significance only after HIIE. On day 2 in both sexes the increases in hepatic TG and PLIN2 with exercise declined toward CON levels. Only HIIE on day 2 resulted in reduced hepatic TG secretion by ∼20% in females with no effect in males. Neither exercise modality altered AMPK signaling or microsomal triglyceride transfer protein expression. Females exhibited higher hepatic TG secretion than males in association with different expression levels of related metabolic enzymes. These intensity-dependent and sex-specific alterations following exercise may have implications for sex-based exercise prescription.

Sexual dimorphism in the effects of exercise on metabolism of lipids to support resting metabolism

Exercise training is generally a healthful activity and an effective intervention for reducing the risk of numerous chronic diseases including cardiovascular disease and diabetes. This is likely both a result of prevention of weight gain over time and direct effects of exercise on metabolism of lipids and the other macronutrient classes. Importantly, a single bout of exercise can alter lipid metabolism and metabolic rate for hours and even into the day following exercise, so individuals who regularly exercise, even if not performed every single day, overall could experience a substantial change in their resting metabolism that would reduce risk for metabolic diseases. However, resting metabolism does not respond similarly in all individuals to exercise participation, and indeed gender or sex is a major determinant of the response of resting lipid metabolism to prior exercise. In order to fully appreciate the metabolic effects and health benefits of exercise, the differences between men and women must be considered. In this article, the differences in the effects of exercise on resting metabolic rate, fuel selection after exercise, as well as the shuttling of triglyceride and fatty acids between tissues are discussed. Furthermore, concepts related to sex differences in the precision of homeostatic control and sex differences in the integration of metabolism between various organs are considered.

The effect of high intensity interval exercise on postprandial triacylglycerol and leukocyte activation--monitored for 48 h post exercise

Postprandial phenomenon are thought to contribute to atherogenesis alongside activation of the immune system. A single bout of high intensity interval exercise attenuates postprandial triacylglycerol (TG), although the longevity and mechanisms underlying this observation are unknown. The aims of this study were to determine whether this attenuation in postprandial TG remained 2 days after high intensity interval exercise, to monitor markers of leukocyte activation and investigate the underlying mechanisms. Eight young men each completed two three day trials. On day 1: subjects rested (Control) or performed 5 x 30 s maximal sprints (high intensity interval exercise). On day 2 and 3 subjects consumed high fat meals for breakfast and 3 h later for lunch. Blood samples were taken at various times and analysed for TG, glucose and TG-rich lipoprotein (TRL)-bound LPL-dependent TRL-TG hydrolysis (LTTH). Flow cytometry was used to evaluate granulocyte, monocyte and lymphocyte CD11b and CD36 expression. On day 2 after high intensity interval exercise TG area under the curve was lower (P<0.05) (7.46±1.53 mmol/l/7h) compared to the control trial (9.47±3.04 mmol/l/7h) with no differences during day 3 of the trial. LTTH activity was higher (P<0.05) after high intensity interval exercise, at 2 hours of day 2, compared to control. Granulocyte, monocyte and lymphocyte CD11b expression increased with time over day 2 and 3 of the study (P<0.0001). Lymphocyte and monocyte CD36 expression decreased with time over day 2 and 3 (P<0.05). There were no differences between trials in CD11b and CD36 expression on any leukocytes. A single session of high intensity interval exercise attenuated postprandial TG on day 2 of the study, with this effect abolished by day 3.The reduction in postprandial TG was associated with an increase in LTTH. High intensity interval exercise had no effect on postprandial responses of CD11b or CD36.

The latest on the effect of prior exercise on postprandial lipaemia

This review examines the effect of prior exercise on postprandial triacylglycerol (pTAG) concentrations, an independent risk factor for cardiovascular diseases. Numerous studies have shown that a single bout of exercise reduces pTAG concentrations; however, several modulators such as exercise energy expenditure/deficit, mode of exercise (aerobic/resistance/high intensity/intermittent exercise or combinations), type of meal (moderate or high fat), time frame between exercise and meal and target group may individually or in conjunction influence this effect. On the other hand, at least for aerobic exercise, training reduces pTAG concentrations transiently (~2 days); therefore, exercise sessions should be frequent enough to maintain this clinically significant improvement. For the healthy population, it seems that a subject's preference and ability determine which type of exercise to undertake to attenuate pTAG concentrations; an energy expenditure of ~30 kJ/kg of body mass (or ~2-2.5 MJ) not combined with a corresponding increase in energy intake is required; for resistance or intermittent exercise, for those following a moderate rather than a high-fat diet, and for those with obesity (expressed as kJ/kg of body mass), a smaller energy expenditure is probably sufficient. More studies are needed to investigate dose-response/plateau effects, as well as the threshold of energy expenditure in those with diabetes mellitus and other high-risk populations. Finally, investigation of the underlying mechanisms may be clinically helpful in individualizing the appropriate intervention.

Effect of acute negative and positive energy balance on basal very-low density lipoprotein triglyceride metabolism in women

Background

Acute reduction in dietary energy intake reduces very low-density lipoprotein triglyceride (VLDL-TG) concentration. Although chronic dietary energy surplus and obesity are associated with hypertriglyceridemia, the effect of acute overfeeding on VLDL-TG metabolism is not known.

Objective

The aim of the present study was to investigate the effects of acute negative and positive energy balance on VLDL-TG metabolism in healthy women.

Design

Ten healthy women (age: 22.0±2.9 years, BMI: 21.2±1.3 kg/m²) underwent a stable isotopically labeled tracer infusion study to determine basal VLDL-TG kinetics after performing, in random order, three experimental trials on the previous day: i) isocaloric feeding (control) ii) hypocaloric feeding with a dietary energy restriction of 2.89±0.42 MJ and iii) hypercaloric feeding with a dietary energy surplus of 2.91±0.32 MJ. The three diets had the same macronutrient composition.

Results

Fasting plasma VLDL-TG concentrations decreased by ∼26% after hypocaloric feeding relative to the control trial (P = 0.037), owing to decreased hepatic VLDL-TG secretion rate (by 21%, P = 0.023) and increased VLDL-TG plasma clearance rate (by ∼12%, P = 0.016). Hypercaloric feeding increased plasma glucose concentration (P = 0.042) but had no effect on VLDL-TG concentration and kinetics compared to the control trial.

Conclusion

Acute dietary energy deficit (∼3MJ) leads to hypotriglyceridemia via a combination of decreased hepatic VLDL-TG secretion and increased VLDL-TG clearance. On the other hand, acute dietary energy surplus (∼3MJ) does not affect basal VLDL-TG metabolism but disrupts glucose homeostasis in healthy women.

Effect of high-intensity interval exercise on basal triglyceride metabolism in non-obese men

A single bout of high-intensity interval aerobic exercise has been shown to produce the same or greater metabolic benefits as continuous endurance exercise with considerably less energy expenditure, but whether this applies to very low density lipoprotein (VLDL) metabolism is not known. We sought to examine the effect of a single bout of high-intensity interval aerobic exercise on basal VLDL-triglyceride (TG) kinetics 14 and 48 h after exercise cessation to determine the acute and time-dependent effects of this type of exercise on VLDL-TG metabolism. Eight healthy sedentary men (age, 23.6 ± 6.1 years; body mass index, 23.1 ± 2.2 kg·m(-2), peak oxygen consumption (V̇O2peak), 36.3 ± 5.5 mL·kg(-1)·min(-1)) participated in three stable isotopically labeled tracer infusion studies: (i) 14 h and (ii) 48 h after a single bout of high-intensity aerobic interval exercise (60% and 90% of V̇O2peak in 4 min intervals for a total of 32 min; gross energy expenditure ∼500 kcal) and (iii) after an equivalent period of rest, in random order. Fasting plasma VLDL-TG concentration was 20% lower at 14 h (P = 0.046) but not at 48 h (P = 1.000) after exercise compared with the resting trial. VLDL-TG plasma clearance rate increased by 21% at 14 h (P < 0.001) but not at 48 h (P = 0.299) after exercise compared with rest, whereas hepatic VLDL-TG secretion rate was not different from rest at any time point after exercise. We conclude that high-intensity interval exercise reduces fasting plasma VLDL-TG concentrations in non-obese men the next day by augmenting VLDL-TG clearance, just like a single bout of continuous endurance exercise. This effect is short-lived and abolished by 48 h after exercise.

Acute effects of exercise and calorie restriction on triglyceride metabolism in women

PURPOSE

The mechanisms by which exercise reduces fasting plasma triglyceride (TG) concentrations in women and the effect of negative energy balance independent of muscular contraction are not known.The aim of this study was to evaluate the effects of equivalent energy deficits induced by exercise or calorie restriction on basal VLDL-TG metabolism in women.

METHODS

Eleven healthy women (age = 23.5 ± 2.7 yr, body mass index = 21.6 ± 1.4 kg·m-2; mean ± SD) underwent a stable isotopically labeled tracer infusion study to determine basal VLDL-TG kinetics after performing, in random order, three experimental trials on the previous day: (i) a single exercise bout (brisk walking at 60% of peak oxygen consumption for 123 ± 18 min, with a net energy expenditure of 2.06 ± 0.39 MJ, ∼500 kcal), (ii) dietary energy restriction of 2.10 ± 0.41 MJ, and (iii) a control day of isocaloric feeding and rest (zero energy balance).

RESULTS

Fasting plasma VLDL-TG concentration was approximately 30% lower after the exercise trial compared with the control trial (P < 0.001), whereas no significant change was detected after the calorie restriction trial (P = 0.297 vs control). Relative to the control condition, exercise increased the plasma clearance rate of VLDL-TG by 22% (P = 0.001) and reduced hepatic VLDL-TG secretion rate by approximately 17% (P = 0.042), whereas hypocaloric diet had no effect on VLDL-TG kinetics (P > 0.2).

CONCLUSION

(i) Exercise-induced hypotriglyceridemia in women manifests through a different mechanism (increased clearance and decreased secretion of VLDL-TG) than that previously described in men (increased clearance of VLDL-TG only), and (ii) exercise affects TG homeostasis by eliciting changes in VLDL-TG kinetics that cannot be reproduced by an equivalent diet-induced energy deficit, indicating that these changes are independent of the exercise-induced negative energy balance but instead are specific to muscular contraction.

Effect of exercise on postprandial endothelial function in adolescent boys

The ingestion of high-fat meals induces a state of endothelial dysfunction in adults. This dysfunction is attenuated by prior exercise. The response of young people to these nutritional and physiological stressors has not been established. Thus, the purpose of the present study was to investigate if a bout of moderate-intensity exercise influenced endothelial function (as indicated by flow-mediated dilation (FMD)) following the ingestion of a high-fat breakfast and lunch in adolescent boys (aged 12·6–14·3 years). Two, 2 d main trials (control and exercise) were completed by thirteen adolescent boys in a counter-balanced, cross-over design. Participants were inactive on day 1 of the control trial, but completed 60 min of walking at 60 % peak oxygen uptake in the exercise trial. On day 2, endothelial function was assessed via FMD prior to, and following, ingestion of a high-fat breakfast and lunch. There was no difference in fasting FMD between the control and exercise trial (P= 0·449). In the control trial, FMD was reduced by 32 % following consumption of the high-fat breakfast and by 24 % following lunch. In the exercise trial, the corresponding reductions were 6 and 10 %, respectively (main effect trial, P= 0·002). These results demonstrate that moderate-intensity exercise can attenuate the decline in FMD seen following the consumption of high-fat meals in adolescent boys.

Exercise-associated generation of PPARγ ligands activates PPARγ signaling events and upregulates genes related to lipid metabolism

The aim of the present study was to test the hypotheses that exercise is associated with generation of peroxisome proliferator-activated receptor-γ (PPARγ) ligands in the plasma and that this may activate PPARγ signaling within circulating monocytes, thus providing a mechanism to underpin the exercise-induced antiatherogenic benefits observed in previous studies. A cohort of healthy individuals undertook an 8-wk exercise-training program; samples were obtained before (Pre) and after (Post) standardized submaximal exercise bouts (45 min of cycling at 70% of maximal O2 uptake, determined at baseline) at weeks 0, 4, and 8. Addition of plasma samples to PPARγ response element (PPRE)-luciferase reporter gene assays showed increased PPARγ activity following standardized exercise bouts (Post/Pre = 1.23 ± 0.10 at week 0, P < 0.05), suggesting that PPARγ ligands were generated during exercise. However, increases in PPARγ/PPRE-luciferase activity in response to the same standardized exercise bout were blunted during the training program (Post/Pre = 1.18 ± 0.14 and 1.10 ± 0.10 at weeks 4 and 8, respectively, P > 0.05 for both), suggesting that the relative intensity of the exercise may affect PPARγ ligand generation. In untrained individuals, specific transient increases in monocyte expression of PPARγ-regulated genes were observed within 1.5–3 h of exercise (1.7 ± 0.4, 2.6 ± 0.4, and 1.4 ± 0.1 fold for CD36, liver X receptor-α, and ATP-binding cassette subfamily A member 1, respectively, P < 0.05), with expression returning to basal levels within 24 h. In contrast, by the end of the exercise program, expression at the protein level of PPARγ target genes had undergone sustained increases that were not associated with an individual exercise bout (e.g., week 8 Pre/ week 0 Pre = 2.79 ± 0.61 for CD36, P < 0.05). Exercise is known to upregulate PPARγ-controlled genes to induce beneficial effects in skeletal muscle (e.g., mitochondrial biogenesis and aerobic respiration). We suggest that parallel exercise-induced benefits may occur in monocytes, as monocyte PPARγ activation has been linked to beneficial antidiabetic effects (e.g., exercise-induced upregulation of monocytic PPARγ-controlled genes is associated with reverse cholesterol transport and anti-inflammatory effects). Thus, exercise-triggered monocyte PPARγ activation may constitute an additional rationale for prescribing exercise to type 2 diabetes patients.

Effects of moderate exercise on VLDL₁ and Intralipid kinetics in overweight/obese middle-aged men

Prior moderate exercise reduces plasma triglyceride (TG)-rich lipoprotein concentrations, mainly in the large very low-density lipoprotein (VLDL₁) fraction, but the mechanism responsible is unclear. We investigated the effects of brisk walking on TG-rich lipoprotein kinetics using a novel method. Twelve overweight/obese middle-aged men underwent two kinetic studies, involving infusion of Intralipid to block VLDL₁ catabolism, in random order. On the afternoon prior to infusion, subjects either walked on a treadmill for 2 h at ∼50% maximal oxygen uptake or performed no exercise. Multiple blood samples were taken during and after infusion for separation of Intralipid (S(f) 400) and VLDL₁ (S(f) 60-400). VLDL₁-TG and -apoB production rates were calculated from their linear rises during infusion; fractional catabolic rates (FCR) were calculated by dividing linear rises by fasting concentrations. Intralipid-TG FCR was determined from the postinfusion exponential decay. Exercise reduced fasting VLDL₁-TG concentration by 30% (P = 0.007) and increased TG enrichment of VLDL₁ particles [30% decrease in cholesteryl ester (CE)/TG ratio (P = 0.007); 26% increase in TG/apoB ratio (P = 0.059)]. Exercise also increased VLDL₁-TG, VLDL₁-apoB, and Intralipid-TG FCRs by 82, 146, and 43%, respectively (all P < 0.05), but had no significant effect on VLDL₁-TG or -apoB production rates. The exercise-induced increase in VLDL₁-apoB FCR correlated strongly with the exercise-induced changes in VLDL₁ CE/TG (r = -0.659, r = 0.020) and TG/apoB (r = 0.785, P = 0.002) ratios. Thus, exercise-induced reductions in VLDL₁ concentrations are mediated by increased catabolism, rather than reduced production, which may be facilitated by compositional changes to VLDL₁ particles that increase their affinity for clearance from the circulation.

Is the beneficial effect of prior exercise on postprandial lipaemia partly due to redistribution of blood flow?

Preprandial aerobic exercise lowers postprandial lipaemia (a risk factor for coronary heart disease); however, the mechanisms responsible are still not clear. The present study investigated whether blood flow to skeletal muscle and/or the liver was increased in the postprandial period after exercise, relative to a control trial, and whether this resulted from increased cardiac output or redistribution of flow. Eight overweight inactive males, aged 49.4±10.5 years (mean±S.D.), acted as their own controls in a counterbalanced design, either walking briskly for 90 min at 60% V̇O2max (maximal oxygen uptake), or resting in the lab, on the evening of day 1. The following morning, a fasting blood sample was collected, participants consumed a high-fat breakfast, and further venous blood samples were drawn hourly for 6 h. Immediately after blood sampling, Doppler ultrasound was used to measure cardiac output and blood flow through both the femoral artery of one leg and the hepatic portal vein, with the ultrasonographer blinded to trial order. The total postprandial triacylglycerol response was 22% lower after exercise (P=0.001). Blood flow through the femoral artery and the hepatic portal vein was increased by 19% (P<0.001) and 16% (P=0.033), respectively, during the 6-h postprandial period following exercise; however, postprandial cardiac output did not differ between trials (P=0.065). Redistribution of blood flow, to both exercised skeletal muscle and the liver, may therefore play a role in reducing the plasma triacylglycerol response to a high-fat meal on the day after an exercise bout.

Is the effect of prior exercise on postprandial lipaemia the same for a moderate-fat meal as it is for a high-fat meal?

Moderate-intensity exercise can lower the TAG response to a high-fat meal; however, the British diet is moderate in fat, and no study to date has compared the effect of such exercise on responses to high-fat and moderate-fat meals. The present work investigated the effect of brisk walking performed 13 h before intake of both high-fat and moderate-fat meals on postprandial plasma TAG concentrations. Eight inactive, overweight men completed four separate 2 d trials, i.e. rest (Con) or a 90-min treadmill walk (Ex) on the evening of day 1, followed by the ingestion of a moderate-fat (Mod) or high-fat (High) meal on the morning of day 2. High-fat meals contained 66 % of total energy as fat, while the percentage was 35 % for moderate-fat meals; both the meals were, however, isoenergetic. On day 2, venous blood was sampled in the fasted state, 30 and 60 min after ingesting the test meal and then hourly until 6 h post-meal. Exercise reduced plasma TAG concentrations significantly (P < 0·001), with no exercise × meal interaction (P = 0·459). Walking reduced the total TAG response to a high-fat meal by 29 % (relative to High Con); the same bout of exercise performed before ingesting a moderate-fat meal lowered total TAG by 26 % (compared with Mod Con). The ability of a single moderate-intensity aerobic exercise bout to lower postprandial TAG concentrations is just as great, in percentage terms, when the test meal ingested is of a moderate rather than a high fat content.

Effects of energy balance on postprandial triacylglycerol metabolism

PURPOSE OF REVIEW

To present the effect of negative energy balance on postprandial triacylglycerol concentrations (pTAG), an independent risk factor for the development of cardiovascular disease.

RECENT FINDINGS

Aerobic exercise reduces pTAG; however, recent findings confirm that this effect is only evident with an accompanying energy deficit. Moreover, a recent study showed that acute diet-induced energy deficit also reduces pTAG. The extent of energy deficit required to significantly attenuate pTAG depends on the type of given meal, the type of deficit (aerobic/resistance exercise, diet, or combination of diet and exercise), and patients' health status. Apart from the acute effects, prolonged energy deficit leading to moderate weight loss attenuates pTAG, when it is combined with other known hypotriacylglycerolemic agents, such as carbohydrate restriction.

SUMMARY

For healthy population, it seems that it is up to patient's preference and ability which type of energy deficit will follow to attenuate pTAG; an energy deficit of approximately 30 kJ/kg of body mass is required; for resistance exercise a smaller deficit is probably sufficient. More studies are needed to investigate dose-response/plateau effects, the effects of energy deficit-energy surplus every other day, and the threshold of energy deficit-weight loss in diabetics and other high-risk populations. Finally, investigation of the underlying mechanisms may be clinicall helpful in individualizing the appropriate intervention.

Free fatty acid kinetics in the late phase of postexercise recovery: importance of resting fatty acid metabolism and exercise-induced energy deficit

Free fatty acid (FFA) availability increases several-fold during exercise and remains significantly elevated for at least 3 to 6 hours after exercise cessation. Little, however, is known regarding the duration of the postexercise rise in FFA flux. In the present study, we used stable isotope-labeled palmitate infusion to examine fatty acid metabolism in 27 healthy untrained men and women (age, 29 +/- 7 years; body mass index, 25 +/- 4 kg/m2) between 13 to 16 hours and 21 to 24 hours after a single bout of moderate-intensity endurance exercise (1-2 hours at 60% of peak oxygen consumption), performed in the evening, and after a time-matched resting trial. Postabsorptive FFA rate of appearance (Ra) and FFA concentration in plasma were significantly greater after exercise than rest throughout the recovery period (P < .015), but the exercise-induced increases declined from approximately 40% at 13 to 16 hours to approximately 10% at 21 to 24 hours postexercise (P = .001). The magnitude of the exercise-induced increase in plasma FFA concentration was proportional to the increase in FFA Ra. Correlation analysis demonstrated that exercise-induced changes in plasma FFA Ra at 13 to 16 hours are (1) negatively associated with resting plasma FFA Ra and (2) positively associated with the net energy expenditure of exercise and the exercise-induced changes in whole-body fat oxidation rate (all P values < .05). In multivariate stepwise linear regression analysis, baseline plasma FFA Ra (P < or = .008) and net energy expenditure of exercise (P < or = .005) independently predicted the exercise-induced change in plasma FFA Ra at 13 to 16 hours. We conclude that the exercise-induced increase in FFA mobilization is (1) long-lived, persisting for 12 to 24 hours after exercise, with a progressive decline with time; (2) greater in subjects with low than high resting plasma FFA availability; and (3) greater after exercise with high than low energy demand.

A single bout of whole-body resistance exercise augments basal VLDL-triacylglycerol removal from plasma in healthy untrained men

A single bout of prolonged aerobic exercise lowers plasma TAG (triacylglycerol) concentrations the next day by increasing the efficiency of VLDL (very-low-density lipoprotein)-TAG removal from the circulation. The effect of resistance exercise on VLDL-TAG metabolism is not known. Therefore we evaluated VLDL-TAG kinetics by using stable isotope-labelled tracers in eight healthy untrained men (age, 25.3+/-0.8 years; body mass index, 24.5+/-0.6 kg/m(2)) in the post-absorptive state in the morning on two separate occasions: once after performing a single 90-min bout of strenuous isokinetic resistance exercise (three sets x ten repetitions, 12 exercises at 80% of maximum peak torque production, with a 2-min rest interval between exercises) on the preceding afternoon and once after an equivalent period of rest. Fasting plasma VLDL-TAG concentrations in the morning after exercise were significantly lower than in the morning after rest (0.23+/-0.04 compared with 0.33+/-0.06 mmol/l respectively; P=0.001). Hepatic VLDL-TAG secretion rate was not different (P=0.31), but plasma clearance rate of VLDL-TAG was significantly higher (by 26+/-8%) after exercise than rest (31+/-3 compared with 25+/-3 ml/min respectively; P=0.004), and the mean residence time of VLDL-TAG in the circulation was significantly shorter (113+/-10 compared with 144+/-18 min respectively; P=0.02). Fasting plasma NEFA (non-esterified fatty acid; 'free' fatty acid) and serum beta-hydroxybutyrate concentrations were both significantly higher after exercise than rest (P<0.05), whereas plasma glucose and serum insulin concentrations were not different (P>0.30). We conclude that, in healthy untrained men, a single bout of whole-body resistance exercise lowers fasting plasma VLDL-TAG concentrations by augmenting VLDL-TAG removal from plasma. The effect appears to be qualitatively and quantitatively similar to that reported previously for aerobic exercise.

Basal adipose tissue and hepatic lipid kinetics are not affected by a single exercise bout of moderate duration and intensity in sedentary women

Hypertriacylglycerolaemia is an important risk factor for cardiovascular disease. In men, we have shown that the effects of evening exercise on basal VLDL (very-low-density lipoprotein) metabolism are dose-dependent: a single prolonged bout of aerobic exercise [2 h at 60% of VO(2 peak) (peak oxygen consumption)] reduces fasting plasma TAG [triacylglycerol (triglyceride)] concentrations, via enhanced clearance of VLDL-TAG from the circulation, whereas the same exercise performed for 1 h has no effect on VLDL-TAG metabolism and concentration. We hypothesized that women are more sensitive to the TAG-lowering effect of exercise because they reportedly use more intramuscular TAG as an energy source during exercise, and depletion of muscle TAG stores has been linked to reciprocal changes in skeletal muscle LPL (lipoprotein lipase) activity. To test our hypothesis, we measured basal VLDL-TAG and VLDL-apoB-100 (apolipoprotein B-100), and plasma NEFA [non-esterified fatty acid ('free fatty acid')] kinetics, by using stable isotope-labelled tracer techniques, on the morning after a single session of evening exercise of moderate duration and intensity (1 h at 60% of VO(2 peak)) in eight sedentary pre-menopausal women (age, 28+/-3 years; body mass index, 27+/-2 kg/m(2); body fat, 34+/-3%; values are means+/-S.E.M.). Compared with an equivalent period of evening rest, exercise had no effect on post-absorptive NEFA concentrations and the rate of appearance in plasma, VLDL-TAG and VLDL-apoB-100 concentrations, hepatic VLDL-TAG and VLDL-apoB-100 secretion and plasma clearance rates (all P>0.05). We conclude that, in women, as in men, a single session of exercise of moderate intensity and duration is not sufficient to bring about the alterations in VLDL metabolism that have been linked to post-exercise hypotriacylglycerolaemia.

High-intensity interval aerobic training reduces hepatic very low-density lipoprotein-triglyceride secretion rate in men

A single bout of strenuous endurance exercise reduces fasting plasma triglyceride (TG) concentrations the next day (12-24 h later) by augmenting the efficiency of very low-density lipoprotein (VLDL)-TG removal from the circulation. Although much of the hypotriglyceridemia associated with training is attributed to the last bout of exercise, the relevant changes in VLDL-TG metabolism have never been investigated. We therefore examined basal VLDL-TG kinetics in a group of sedentary young men (n=7) who underwent 2 mo of supervised high-intensity interval training (3 sessions/wk; running at 60 and 90% of peak oxygen consumption in 4-min intervals for a total of 32 min; gross energy expenditure: 446+/-29 kcal) and a nonexercising control group (n=8). Each subject completed two stable isotope-labeled tracer infusion studies in the postabsorptive state, once before and again after the intervention (approximately 48 h after the last exercise bout in the training group). Peak oxygen consumption increased by approximately 18% after training (P <or= 0.05), whereas body weight and body composition were not altered. Fasting plasma VLDL-TG concentration was reduced after training by approximately 28% (P <or= 0.05), and this was due to reduced hepatic VLDL-TG secretion rate (by approximately 35%, P <or= 0.05) with no changes (<5%, P>0.7) in VLDL-TG plasma clearance rate and the mean residence time of VLDL-TG in the circulation. No significant changes in VLDL-TG concentration and kinetics were observed in the nonexercising control group (all P >or= 0.3). We conclude that a short period of high-intensity interval aerobic training lowers the rate of VLDL-TG secretion by the liver in previously sedentary men. This is different from the mechanism underlying the hypotriglyceridemia of acute exercise; however, it remains to be established whether our finding reflects an effect of the longer time lapse from the last exercise bout, an effect specific to the type of exercise performed, or an effect of aerobic training itself.

Estimated liver weight is directly related to hepatic very low-density lipoprotein-triglyceride secretion rate in men

BACKGROUND

Animal studies suggest that liver weight is directly related to hepatic very low-density lipoprotein-triglyceride (VLDL-TG) secretion, independently of body size. This relationship has never been examined in humans.

MATERIALS AND METHODS

We measured VLDL-TG secretion rate by using stable isotope-labelled tracers in 21 healthy, non-obese men (age: 25 +/- 3 years; body mass index: 24.8 +/- 1.6 kg m(-2)), and evaluated the relationship between VLDL-TG secretion and indices of total and regional adiposity (body mass index, total body fat, trunk fat), metabolic parameters (free fatty acid, glucose, and insulin concentrations, homeostasis model assessment index of insulin resistance, resting energy expenditure), and estimated liver weight.

RESULTS

Correlation analysis showed that estimated liver weight was positively associated with total VLDL-TG secretion rate (r = 0.722, P < 0.001), VLDL-TG secretion rate per liter of plasma (r = 0.562, P = 0.008), VLDL-TG secretion rate per kilogram of body weight (r = 0.555, P = 0.009), and VLDL-TG secretion rate per kilogram of liver weight (r = 0.620, P = 0.003). In multiple regression analysis, estimated liver weight was the only significant predictor of VLDL-TG secretion rate regardless of units of expression, explaining 31-52% of total variance; none of the metabolic parameters and indices of body fatness entered the regression models.

CONCLUSIONS

We conclude that estimated liver weight is directly related to hepatic VLDL-TG secretion rate in healthy non-obese men; this relationship is likely not mediated by interindividual variation in body size.

Acute exercise-induced changes in basal VLDL-triglyceride kinetics leading to hypotriglyceridemia manifest more readily after resistance than endurance exercise

Resistance training is considered less effective than endurance training in lowering plasma triglyceride (TG) concentrations. Acutely, however, a single bout of strenuous exercise, whether endurance or resistance, increases the efficiency of very low-density lipoprotein (VLDL)-TG removal from the circulation and leads to hypotriglyceridemia. The comparative effects of these two types of exercise on VLDL-TG metabolism are not known. We therefore examined basal VLDL-TG kinetics by using stable isotope-labeled tracers in seven healthy, nonobese, untrained young men in the postabsorptive state, the morning after a single 90-min bout of either low-intensity endurance exercise (approximately 30% of peak oxygen consumption) or high-intensity resistance exercise (3 sets of 10 repetitions for 12 exercises at 80% of peak torque production), matched for total energy expenditure (approximately 400 kcal), or an equivalent period of rest on the preceding afternoon. Compared with rest, resistance exercise lowered fasting plasma VLDL-TG concentration by -28 +/- 10% (P = 0.034), increased VLDL-TG plasma clearance rate by 30 +/- 8% (P = 0.003), and shortened the mean residence time (MRT) of VLDL-TG in the circulation by -36 +/- 11 min (P = 0.016), whereas endurance exercise had no effect (all P > 0.05). Basal VLDL-TG plasma clearance rate was greater (P = 0.003) and VLDL-TG MRT was shorter (P = 0.012) the morning after resistance than endurance exercise. We conclude that, for the same total energy expenditure, resistance exercise is more potent than endurance exercise in eliciting changes in VLDL-TG metabolism that have been linked with hypotriglyceridemia, and it should thus be considered as an alternative to or in addition to endurance exercise for the control of plasma TG concentrations.

Exercise of low energy expenditure along with mild energy intake restriction acutely reduces fasting and postprandial triacylglycerolaemia in young women

A single bout of prolonged, moderate-intensity endurance exercise lowers fasting and postprandial TAG concentrations the next day. However, the TAG-lowering effect of exercise is dose-dependent and does not manifest after light exercise of low energy cost ( < 2 MJ). We aimed to investigate whether superimposing mild energy intake restriction to such exercise, in order to augment total energy deficit, potentiates the hypotriacylglycerolaemic effect. Eight healthy, sedentary, premenopausal women (age 27.1 (sem 1.3) years; BMI 21.8 (sem 0.9) kg/m2) performed two oral fat tolerance tests in the morning on two different occasions: once after a single bout of light exercise (100 min at 30 % of peak oxygen consumption; net energy expenditure 1.04 (sem 0.01) MJ) coupled with mild energy intake restriction (1.39 (sem 0.22) MJ) on the preceding day, and once after resting coupled with isoenergetic feeding on the preceding day (control). Fasting plasma TAG, TAG in the TAG-rich lipoproteins (TRL-TAG) and serum insulin concentrations were 18, 34 and 30 % lower, respectively, after exercise plus diet compared with the control trial (P < 0.05). Postprandial concentrations of plasma TAG and TRL-TAG were 19 and 27 % lower after exercise plus diet compared with the control condition (P < 0.01), whereas postprandial insulin concentrations were not different. It is concluded that a combination of light exercise along with mild hypoenergetic diet may be a practical and feasible intervention to attenuate fasting and postprandial triacylglycerolaemia, especially for people who cannot exercise for prolonged periods of time at moderate-to-high intensities, such as many sedentary individuals.

Exercise Rehabilitation in Pediatric Cardiomyopathy

Children with cardiomyopathy carry significant risk of morbidity and mortality. New research and technology have brought about significant advancements to the diagnosis and clinical management of children with cardiomyopathy. However, currently heart transplantation remains the standard of care for children with symptomatic and progressive cardiomyopathy. Cardiovascular rehabilitation programs have yielded success in improving cardiac function, overall physical activity, and quality of life in adults with congestive heart failure from a variety of conditions. There is encouraging and emerging data on its effects in children with chronic illness and with its proven benefits in other pediatric disorders, the implementation of a program for with cardiomyopathy should be considered. Exercise rehabilitation programs may improve specific endpoints such quality of life, cardiovascular function and fitness, strength, flexibility, and metabolic risk. With the rapid rise in pediatric obesity, children with cardiomyopathy may be at similar risk for developing these modifiable risk factors. However, there are potentially more detrimental effects of inactivity in this population of children. Future research should focus on the physical and social effects of a medically supervised cardiac rehabilitation program with correct determination of the dosage and intensity of exercise for optimal benefits in this special population of children. It is imperative that more detailed recommendations for children with cardiomyopathy be made available with evidence-based research.