Validity and reliability of a novel metabolic flexibility test in children with obesity

Timing matters: diurnal variation of maximal fat oxidation and substrate oxidation rates in metabolic syndrome-a randomized crossover study

PURPOSE

The aim of this study was to investigate if diurnal oscillation in maximal fat oxidation (MFO) and substrate oxidation rates during exercise exists in subjects with metabolic syndrome (MetS).

METHODS

In a randomized crossover design, 14 MetS patients were assigned to two graded exercise tests conditions performed in the morning (between 7:00 and 9:00 a.m) and in the afternoon (between 4:00 and 5:00 p.m). MFO was defined as the highest absolute value of fat oxidation obtained from the average of last 2-min stages during an indirect calorimetry test.

RESULTS

MFO increased by 20.6% from morning to afternoon (p = 0.0002, Cohen's d = 0.52). There was a significant time of day, (p < 0.0001, η2p = 0.76) and intensity effect (p = 0.002, η2p = 0.32) in fat oxidation (Fatox) rates indicating that Fatox was higher in the afternoon than in the morning.

CONCLUSION

Our study extends previous findings on the existence of diurnal variation in maximal fat oxidation to MetS patients, highlighting the afternoon as a more favorable time for fat utilization during exercise. These findings have practical implications for optimizing training timing in MetS patients.

TRIAL REGISTRATION NUMBER

PACTR202306776991260.

Metabolic Flexibility During Exercise in Children with Overweight/Obesity Versus Children who are Lean

PURPOSE

This study examined metabolic flexibility with respect to fat metabolism during exercise in children who are lean (n=11; 10.9[0.9] y) and overweight/obese (OW/OB; n=9; 10.3[1.2] y).

METHOD

Participants were grouped based on body mass index percentiles for age and sex. Groups were mixed in age and sex. Participants completed two 20-minute exercise bouts on a cycle ergometer, separated by a 10-minute rest. Bout 1 consisted of 10 minutes at 50% VO2peak and 10 minutes at 75% VO2peak. Bout 2 was 20 minutes at 50% VO2peak. Absolute fat oxidation rate (FOR), FOR relative to body mass, FOR relative to fat-free mass, and proportional fat use were measured at 10 minutes of bout 1 and 5, 10, 15, and 20 minutes of bout 2.

RESULTS

Absolute FOR was higher in the OW/OB group (range: 117.8 [55.1]-206.2 [48.3] mg·min-1) than in the lean group (81.1 [32.2]-152.2 [38.2] mg·min-1); however, there were no significant main effects for group or significant interactions for proportional fat use, FOR relative to body mass, or FOR relative to fat-free mass.

CONCLUSION

Children in this age range who are overweight/obese do not display impaired metabolic flexibility with respect to fat metabolism during exercise.

Serum metabolomic biomarkers of perceptual speed in cognitively normal and mildly impaired subjects with fasting state stratification

Cognitive decline is associated with both normal aging and early pathologies leading to dementia. Here we used quantitative profiling of metabolites involved in the regulation of inflammation, vascular function, neuronal function and energy metabolism, including oxylipins, endocannabinoids, bile acids, and steroid hormones to identify metabolic biomarkers of mild cognitive impairment (MCI). Serum samples (n = 212) were obtained from subjects with or without MCI opportunistically collected with incomplete fasting state information. To maximize power and stratify the analysis of metabolite associations with MCI by the fasting state, we developed an algorithm to predict subject fasting state when unknown (n = 73). In non-fasted subjects, linoleic acid and palmitoleoyl ethanolamide levels were positively associated with perceptual speed. In fasted subjects, soluble epoxide hydrolase activity and tauro-alpha-muricholic acid levels were negatively associated with perceptual speed. Other cognitive domains showed associations with bile acid metabolism, but only in the non-fasted state. Importantly, this study shows unique associations between serum metabolites and cognitive function in the fasted and non-fasted states and provides a fasting state prediction algorithm based on measurable metabolites.

Metabolic Flexibility during Exercise in Children with Obesity and Matched Controls

BACKGROUND

Impaired metabolic flexibility (MetFlex) could contribute to ectopic fat accumulation and pathological conditions, such as type 2 diabetes. MetFlex refers to the ability to adapt substrate oxidation to availability. To the best of our knowledge, no studies have examined MetFlex under exercise conditions in children with obesity (OB) compared with a control group (CON) without obesity. Therefore, the primary objective was to compare MetFlex during exercise in children with OB compared with CON matched for chronological age, sex, and biological maturation. A better understanding of MetFlex could help elucidate its role in the pathogenesis of childhood obesity and insulin resistance.

METHODS

Children with obesity and without obesity age 8 to 17 yr attended two visits, which included anthropometric measurements, blood work (OB group only), a maximal aerobic fitness (V˙O2max) test, and MetFlex test with a C-enriched carbohydrate (1.75 g per kg of body mass, up to 75 g) ingested before 60 min of exercise at 45% V˙O2max. Breath measurements were collected to calculate exogenous CHO (CHOexo) oxidative efficiency as a measure of MetFlex.

RESULTS

CHOexo oxidative efficiency (CHOexo oxidized/CHO ingested × 100) during exercise was significantly lower in OB (17.3% ± 4.0%) compared with CON (22.6% ± 4.7%, P < 0.001). CHOexo contributed less to total energy expenditure during exercise in OB compared with CON (P < 0.001), whereas the contribution of endogenous CHO (P = 0.19) and total fat was not significantly different (P = 0.91).

CONCLUSIONS

The ability to oxidize oral CHO, an indicator of MetFlex, was 23.5% lower in children with obesity compared with controls, independent of age, sex, and pubertal effects. Thus, obesity at a young age could be associated with reduced MetFlex and future comorbidities.