Energy substrate utilization with and without exogenous carbohydrate intake in boys and men exercising in the heat

Little is known about energy yield during exercise in the heat in boys compared with men. To investigate substrate utilization with and without exogenous carbohydrate (CHOexo) intake, seven boys [11.2 ± 0.2 (SE) yr] and nine men (24.0 ± 1.1 yr) cycled (4 × 20-min bouts) at a fixed metabolic heat production ( Ḣ p) per unit body mass (6 W/kg) in a climate chamber (38°C and 50% relative humidity), on two occasions. Participants consumed a 13C-enriched 8% CHO beverage (CARB) or placebo beverage (CONT) in a double-blinded, counterbalanced manner. Substrate utilization was calculated for the last 60 min of exercise. CHOexo oxidation rate (2.0 ± 0.3 vs. 2.5 ± 0.2 mg·kg fat-free mass−1·min−1, P = 0.02) and CHOexo oxidation efficiency (12.8 ± 0.6 vs. 16.0 ± 0.9%, P = 0.01) were lower in boys compared with men exercising in the heat. Total carbohydrate (CHOtotal), endogenous CHO (CHOendo), and total fat (Fattotal) remained stable in boys and men ( P > 0.05) during CARB, whereas CHOtotal oxidation rate decreased ( P < 0.001) and Fattotal oxidation rate increased over time similarly in boys and men during CONT ( P < 0.001). The relative contribution of CHOexo to total energy yield increased over time in both groups ( P < 0.001). In conclusion, endogenous substrate metabolism and the relative contribution of fuels to total energy yield were not different between groups. The ingestion of a CHO beverage during exercise in the heat may be as beneficial for boys as men to spare endogenous substrate.

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Oxidation rate of exogenous carbohydrate during exercise is higher in boys than in men

Journal of Applied Physiology ◽

10.1152/japplphysiol.00140.2002 ◽

2003 ◽

Vol 94 (1) ◽

pp. 278-284 ◽

Cited By ~ 65

Author(s):

Brian W. Timmons ◽

Oded Bar-Or ◽

Michael C. Riddell

Keyword(s):

Total Energy ◽

Oxidation Rate ◽

Relative Proportion ◽

Fat Oxidation ◽

Substrate Utilization ◽

Pubertal Status ◽

Pubertal Boys ◽

Total Fat ◽

Relative Utilization

To determine whether the relative utilization of exogenous carbohydrate (CHOexo) differs between children and adults, substrate utilization during 60 min of cycling at 70% peak O2 uptake was studied in 12 pre- and early pubertal boys (9.8 ± 0.1 yr) and 10 men (22.1 ± 0.5 yr) on two occasions. Subjects consumed either a placebo or a13C-enriched 6% CHOexo beverage (total volume per trial: 24 ml/kg). Substrate utilization was calculated for the final 30 min of exercise. During both trials, total fat oxidation was higher (5.4 ± 0.5 vs. 3.0 ± 0.4 mg · kg−1 · min−1, P < 0.001) and total CHO oxidation lower (27.4 ± 1.5 vs. 34.8 ± 1.2 mg · kg−1 · min−1, P < 0.001) in boys than in men, respectively. During the CHOexo trial, CHOexo oxidation was higher ( P < 0.001) in boys (8.8 ± 0.5 mg · kg−1 · min−1) than in men (6.2 ± 0.5 mg · kg−1 · min−1) and provided a greater ( P < 0.001) relative proportion of total energy in boys (21.8 ± 1.4%) than in men (14.6 ± 0.9%). These results suggest that, although endogenous CHO utilization during exercise is lower, the relative oxidation of ingested CHO is considerably higher in boys than in men. The greater reliance on CHOexo in boys may be important in preserving endogenous fuels and may be related to pubertal status.

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Design of the oxygen and substrate pathways. III. Partitioning energy provision from carbohydrates.

Journal of Experimental Biology ◽

10.1242/jeb.199.8.1659 ◽

1996 ◽

Vol 199 (8) ◽

pp. 1659-1666 ◽

Cited By ~ 5

Author(s):

J M Weber ◽

T J Roberts ◽

R Vock ◽

E R Weibel ◽

C R Taylor

Keyword(s):

Total Energy ◽

Aerobic Capacity ◽

Indirect Calorimetry ◽

Glucose Oxidation ◽

Muscle Cells ◽

Carbohydrate Oxidation ◽

Total Carbohydrate ◽

Relative Contribution ◽

Glycogen Stores

This paper quantifies maximal fluxes through the pathway supplying carbohydrates to the mitochondria of muscle cells. Continuous infusions of D-[3-(3)H]glucose together with indirect calorimetry were used to investigate the partitioning of the supply of carbohydrates through the two branches of the pathway: from circulating glucose and from glycogen stores within the muscle cells to the mitochondria. The relative contribution of circulating glucose to total carbohydrate oxidation was small, accounting for only 13% and 23% of the carbohydrate oxidized at exercise intensities approaching MO2max in dogs and goats, respectively. Unexpectedly, maximal rates of circulating glucose oxidation were nearly the same in the two species (when expressed in absolute terms; dog:goat ratio = 1.2), despite the 2.2-fold difference in aerobic capacity. We conclude that the glycogen stores in the muscle cells are the major source of substrates at maximal rates of oxidation, supplying 60-70% of the total energy. Furthermore, it is this branch of the carbohydrate pathway that is adapted to the large difference in aerobic capacity between dogs and goats.

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β-Adrenergically Stimulated Fat Oxidation Is Diminished in Middle-Aged Compared to Young Subjects*

The Journal of Clinical Endocrinology & Metabolism ◽

10.1210/jcem.84.10.6043 ◽

1999 ◽

Vol 84 (10) ◽

pp. 3764-3769

Author(s):

E. E. Blaak ◽

M. A. van Baak ◽

W. H. M. Saris

Keyword(s):

Skeletal Muscle ◽

Energy Expenditure ◽

Total Energy ◽

Fat Oxidation ◽

Substrate Utilization ◽

Total Energy Expenditure ◽

Adrenergic Stimulation ◽

Middle Aged ◽

Older Subjects ◽

Young Subjects

Abstract The effect of aging on β-adrenergically mediated substrate utilization was investigated in nine young (25.2 ± 1.7 yr old) and eight older males (52.9 ± 2.1 yr old), matched for body weight and body composition. In a first experiment, the nonselectiveβ -agonist isoprenaline (ISO) was infused in increasing standardized doses, and during each infusion period energy expenditure and substrate utilization were determined by indirect calorimetry. In a second experiment, forearm skeletal muscle metabolism was studied during a standardized infusion dose of ISO (19 ng/kg fat-free mass·min). During β-adrenergic stimulation there was an increased carbohydrate oxidation (at an ISO infusion dose of 24 ng/kg fat-free mass·min, 31% vs. 21% of total energy expenditure; P < 0.05) and a decreased fat oxidation (51 vs. 62 of total energy expenditure; P < 0.05) in older compared to young subjects. Skeletal muscle lactate release significantly increased in the older subjects (from −175 ± 32 to −366 ± 66 nmol/100 mL forearm tissue·min), whereas there was no change in young subjects (from− 32 ± 21 to 23 ± 57 nmol/100 mL forearm tissue·min; interaction group × ISO, P < 0.01). Additionally, there was a tendency toward a blunted ISO-induced increase in nonesterified fatty acid uptake in the older subjects (interaction group × ISO, P = 0.062). Thus, middle-aged subjects have a blunted ability to oxidize fat during β-adrenergic stimulation compared to young subjects. This diminished fat oxidation may be an important etiological factor in the age-related increase in body fatness and obesity by favoring fat storage above oxidation.

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Energy Expenditure and Body Fat Distribution in Mohawk Children

PEDIATRICS ◽

10.1542/peds.95.1.89 ◽

1995 ◽

Vol 95 (1) ◽

pp. 89-95

Author(s):

Michael I. Goran ◽

Mary Kaskoun ◽

Rachel Johnson ◽

Charlene Martinez ◽

Benson Kelly ◽

...

Keyword(s):

Physical Activity ◽

Body Composition ◽

Native Americans ◽

Energy Expenditure ◽

Total Energy ◽

Body Fat ◽

Resting Energy Expenditure ◽

Fat Distribution ◽

Total Energy Expenditure ◽

Fat Free Mass

Objective. Epidemiologic studies suggest that Native Americans, including the Mohawk people, have a high prevalence of obesity, diabetes, and cardiovascular risk. However, current information on alterations in related variables such as energy metabolism and body composition in Native Americans is almost exclusively limited to already obese Pima adults living in the Southwest. The aim of this study was to characterize energy metabolism and body composition in young Mohawk children (17 girls, 11 boys; aged 4 to 7 years) as compared to Caucasian children (36 girls, 34 boys; aged 4 to 7 years). Total energy expenditure was measured by doubly labeled water, postprandial resting energy expenditure by indirect calorimetry, and activity energy expenditure was derived from the difference between total and resting energy expenditure. Fat and fat free mass were estimated from bioelectrical resistance, and body fat distribution was estimated from skinfolds and circumferences. Results. There were no significant effects of ethnic background or sex on body weight, height, or body mass index. Fat free mass was significantly higher in boys and fat mass was significantly higher in girls, with no effect of ethnic background. Chest skinfold thickness, the ratio of trunk skinfolds:extremity skinfolds, and the waist:hip ratio were significantly higher in Mohawk children by 2.5 mm, 0.09 units, and 0.03 units, respectively, independent of sex and fat mass. Total energy expenditure was significantly higher in Mohawk children compared to Caucasian (100 kcal/day in girls, 150 kcal/day in boys), independent of fat free mass and sex, due to a significantly higher physical activity-related energy expenditure. Conclusion. These data suggest that: 1) body fat is more centrally distributed in Mohawk relative to Caucasian children, and this effect is independent of sex and body fat content; 2) Mohawk children have a greater total energy expenditure than Caucasian children, independent of fat free mass, due to greater physical activity-related energy expenditure.

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Effects of creatine loading and prolonged creatine supplementation on body composition, fuel selection, sprint and endurance performance in humans

Clinical Science ◽

10.1042/cs1040153 ◽

2003 ◽

Vol 104 (2) ◽

pp. 153-162 ◽

Cited By ~ 10

Author(s):

Luc J.C. van LOON ◽

Audrey M. OOSTERLAAR ◽

Fred HARTGENS ◽

Matthijs K.C. HESSELINK ◽

Rodney J. SNOW ◽

...

Keyword(s):

Body Composition ◽

Creatine Supplementation ◽

Time Trial ◽

Oxidative Capacity ◽

Substrate Utilization ◽

Cycle Ergometer ◽

Fat Free Mass ◽

Whole Body ◽

Total Creatine ◽

Trial Performance

Most research on creatine has focused on short-term creatine loading and its effect on high-intensity performance capacity. Some studies have investigated the effect of prolonged creatine use during strength training. However, studies on the effects of prolonged creatine supplementation are lacking. In the present study, we have assessed the effects of both creatine loading and prolonged supplementation on muscle creatine content, body composition, muscle and whole-body oxidative capacity, substrate utilization during submaximal exercise, and on repeated supramaximal sprint, as well as endurance-type time-trial performance on a cycle ergometer. Twenty subjects ingested creatine or a placebo during a 5-day loading period (20g·day-1) after which supplementation was continued for up to 6 weeks (2g·day-1). Creatine loading increased muscle free creatine, creatine phosphate (CrP) and total creatine content (P<0.05). The subsequent use of a 2g·day-1 maintenance dose, as suggested by an American College of Sports Medicine Roundtable, resulted in a decline in both the elevated CrP and total creatine content and maintenance of the free creatine concentration. Both short- and long-term creatine supplementation improved performance during repeated supramaximal sprints on a cycle ergometer. However, whole-body and muscle oxidative capacity, substrate utilization and time-trial performance were not affected. The increase in body mass following creatine loading was maintained after 6 weeks of continued supplementation and accounted for by a corresponding increase in fat-free mass. This study provides definite evidence that prolonged creatine supplementation in humans does not increase muscle or whole-body oxidative capacity and, as such, does not influence substrate utilization or performance during endurance cycling exercise. In addition, our findings suggest that prolonged creatine ingestion induces an increase in fat-free mass.

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Substrate utilization and oxygen consumption by canine jejunal mucosa in vitro

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1975.229.1.139 ◽

1975 ◽

Vol 229 (1) ◽

pp. 139-143 ◽

Cited By ~ 10

Author(s):

RG Lester ◽

E Grim

Keyword(s):

Oxygen Consumption ◽

Carbon Dioxide Production ◽

Substrate Utilization ◽

Mean Value ◽

Jejunal Mucosa ◽

Single Animal ◽

Endogenous Substrate ◽

Time Basis

Oxygen consumption, carbon dioxide production, and substrate utilization by small pieces of canine jejunal mucosa have been measured in vitro. In the absence of added substrate, the Qo2 was 0.21 mumol/h per mg dry wt and the respiratory quotient (RQ) was 0.73 indicating the endogenous substrate to be lipid in nature. When glucose or galactose was added, Qo2 and RQ increased. Metabolism of the endogenous substrate was depressed by fructose but not by glucose or galactose. Less than 15% of the metabolized glucose and fructose was degraded to Co2; 80% of the metabolized glucose was recovered as lactate. Galactose disappeared at one-seventh the rate of glucose, but 40% of that metabolized was degrated to CO2. In all experiments Qo2 showed marked cyclic fluctuations with an amplitude of 30-40% of the mean value and a period of 30-40 min. For tissues from a single animal, the cycles were in phase on a clock time basis, indicating that the cycles were synchronized by some in vivo mechanism.

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Carbohydrate Intake in Early Childhood and Body Composition and Metabolic Health: Results from the Generation R Study

Nutrients ◽

10.3390/nu12071940 ◽

2020 ◽

Vol 12 (7) ◽

pp. 1940

Author(s):

Anh N. Nguyen ◽

Susana Santos ◽

Kim V. E. Braun ◽

Trudy Voortman

Keyword(s):

Early Childhood ◽

Body Composition ◽

Hdl Cholesterol ◽

Population Based ◽

Metabolic Health ◽

Carbohydrate Intake ◽

Fat Free Mass ◽

Total Carbohydrate ◽

Blood Concentrations

High sugar intake in childhood has been linked to obesity. However, the role of macronutrient substitutions and associations with metabolic health remain unclear. We examined associations of carbohydrate intake and its subtypes with body composition and metabolic health among 3573 children participating in a population-based cohort in the Netherlands. Intake of total carbohydrate, monosaccharides and disaccharides, and polysaccharides at age 1 year was assessed with a food-frequency questionnaire. We repeatedly measured children’s height and weight to calculate BMI between their ages of 1 and 10 years. At ages 6 and 10 years, fat and fat-free mass were measured with dual-energy X-ray-absorptiometry and blood concentrations of triglycerides, cholesterol, and insulin were obtained. For all outcomes, we calculated age and sexspecific SD-scores. In multivariable-adjusted linear mixed models, we found no associations of intake of carbohydrates or its subtypes with children’s BMI or body composition. A higher intake of monosaccharides and disaccharides was associated with higher triglyceride concentrations (0.02 SDS per 10 g/day, 95% CI: 0.01, 0.04). Higher monosaccharide and disaccharide intake was also associated with lower HDL-cholesterol (−0.03 SDS, 95% CI: −0.04; −0.01), especially when it replaced polysaccharides. Overall, our findings suggest associations of higher monosaccharide and disaccharide intake in early childhood with higher triglyceride and lower HDL-cholesterol concentrations, but do not support associations with body composition.

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Gender differences in substrate utilization during submaximal exercise in endurance-trained subjects

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00266.2001 ◽

2002 ◽

Vol 282 (2) ◽

pp. E435-E447 ◽

Cited By ~ 133

Author(s):

Carsten Roepstorff ◽

Charlotte H. Steffensen ◽

Marianne Madsen ◽

Bente Stallknecht ◽

Inge-Lis Kanstrup ◽

...

Keyword(s):

Oxygen Uptake ◽

Energy Content ◽

Low Density Lipoprotein ◽

Density Lipoprotein ◽

Substrate Utilization ◽

Peak Oxygen Uptake ◽

Submaximal Exercise ◽

Activity Level ◽

Relative Contribution ◽

History Of

Substrate utilization across the leg during 90 min of bicycle exercise at 58% of peak oxygen uptake (V˙o 2 peak) was studied in seven endurance-trained males and seven endurance-trained, eumenorrheic females by applying arteriovenous catheterization, stable isotopes, and muscle biopsies. The female and male groups were matched according toV˙o 2 peak per kilogram of lean body mass, physical activity level, and training history of the subjects. All subjects consumed the same diet, well controlled in terms of nutrient composition as well as energy content, for 8 days preceding the experiment, and all females were tested in the midfollicular phase of the menstrual cycle. During exercise, respiratory exchange ratio (RER) and leg respiratory quotient (RQ) were similar in females and males. Myocellular triacylglycerol (TG) degradation was negligible in males but amounted to 12.4 ± 3.2 mmol/kg dry wt in females and corresponded to 25.0 ± 6.0 and 5.0 ± 7.3% of total oxygen uptake in females and males, respectively ( P < 0.05). Utilization of plasma fatty acids (12.0 ± 2.5 and 9.6 ± 1.5%), blood glucose (13.6 ± 1.5 and 14.3 ± 1.5%), and glycogen (48.5 ± 4.9 and 42.8 ± 2.1%) were similar in females and males. Thus, in females, measured substrate oxidation accounted for 99% of the leg oxygen uptake, whereas in males 28% of leg oxygen uptake was unaccounted for in terms of measured oxidized lipid substrates. These findings may indicate that males utilized additional lipid sources, presumably very low density lipoprotein-TG or TG located between muscle fibers. On the basis of RER and leg RQ, it is concluded that no gender difference existed in the relative contribution from carbohydrate and lipids to the oxidative metabolism across the leg during submaximal exercise at the same relative workload. However, an effect of gender appears to occur in the utilization of the different lipid sources.

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