Impact of methods for data selection on the day-to-day reproducibility of resting metabolic rate assessed with four different metabolic carts.

BACKGROUND AND AIMS: Accomplishing a high day-to-day reproducibility is important to detect changes in resting metabolic rate (RMR) and respiratory exchange ratio (RER) that may be produced after an intervention or for monitoring patients' metabolism over time. We aimed to analyze: (i) the influence of different methods for selecting indirect calorimetry data on RMR and RER assessments; and, (ii) whether these methods influence RMR and RER day-to-day reproducibility. METHODS AND RESULTS: Twenty-eight young adults accomplished 4 consecutive RMR assessments (30-min each), using the Q-NRG (Cosmed, Rome, Italy), the Vyntus CPX (Jaeger-CareFusion, Höchberg, Germany), the Omnical (Maastricht Instruments, Maastricht, The Netherlands), and the Ultima CardiO2 (Medgraphics Corporation, St. Paul, Minnesota, USA) carts, on 2 consecutive mornings. Three types of methods were used: (i) short (periods of 5 consecutive minutes; 6-10, 11-15, 16-20, 21-25, and 26-30 min) and long time intervals (TI) methods (6-25 and 6-30 min); (ii) steady state (SSt methods); and, (iii) methods filtering the data by thresholding from the mean RMR (filtering methods). RMR and RER were similar when using different methods (except RMR for the Vyntus and RER for the Q-NRG). Conversely, using different methods impacted RMR (all P ≤ 0.037) and/or RER (P ≤ 0.009) day-to-day reproducibility in all carts. The 6-25 min and the 6-30 min long TI methods yielded more reproducible measurements for all metabolic carts. CONCLUSION: The 6-25 min and 6-30 min should be the preferred methods for selecting data, as they result in the highest day-to-day reproducibility of RMR and RER assessments.

Fecal microbiota composition is related to brown adipose tissue 18F-fluorodeoxyglucose uptake in young adults.

OBJECTIVE: Human brown adipose tissue (BAT) has gained considerable attention as a potential therapeutic target for obesity and its related cardiometabolic diseases; however, whether the gut microbiota might be an efficient stimulus to activate BAT metabolism remains to be ascertained. We aimed to investigate the association of fecal microbiota composition with BAT volume and activity and mean radiodensity in young adults. METHODS: 82 young adults (58 women, 21.8 ± 2.2 years old) participated in this cross-sectional study. DNA was extracted from fecal samples and 16S rRNA sequencing was performed to analyse the fecal microbiota composition. BAT was determined via a static 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography-computed tomography scan (PET/CT) after a 2 h personalized cooling protocol. 18F-FDG uptake was also quantified in white adipose tissue (WAT) and skeletal muscles. RESULTS: The relative abundance of Akkermansia, Lachnospiraceae sp. and Ruminococcus genera was negatively correlated with BAT volume, BAT SUVmean and BAT SUVpeak (all rho ≤ - 0.232, P ≤ 0.027), whereas the relative abundance of Bifidobacterium genus was positively correlated with BAT SUVmean and BAT SUVpeak (all rho ≥ 0.262, P ≤ 0.012). On the other hand, the relative abundance of Sutterellaceae and Bifidobacteriaceae families was positively correlated with 18F-FDG uptake by WAT and skeletal muscles (all rho ≥ 0.213, P ≤ 0.042). All the analyses were adjusted for the PET/CT scan date as a proxy of seasonality. CONCLUSION: Our results suggest that fecal microbiota composition is involved in the regulation of BAT and glucose uptake by other tissues in young adults. Further studies are needed to confirm these findings. CLINICAL TRIAL INFORMATION: ClinicalTrials.gov no. NCT02365129 (registered 18 February 2015).

Congruent validity and inter-day reliability of two breath by breath metabolic carts to measure resting metabolic rate in young adults.

BACKGROUND & AIMS: Achieving high inter-day reliability is a key factor to analyze the magnitude of change in RMR, for instance after an intervention. The aims of this study were: i) to determine the congruent validity of RMR and respiratory quotient (RQ) with two breath by breath commercially available metabolic carts [CCM Express (CCM) and Ultima CardiO2 (MGU)]; and ii) to analyze the inter-day reliability of RMR and RQ measurements. METHODS & RESULTS: Seventeen young adults participated in the study. RMR measurements were performed during two consecutive 30-min periods, on two consecutive days with both metabolic carts. The 5-min period that met the steady state criteria [Coefficient of variance (CV) < 10% for VO2, VCO2, and VE, and CV<5% for RQ] and with the lowest CV average was included in further analysis. RMR values were higher with the MGU than with the CCM on both days (two-way ANOVA, P = 0.021), however, no differences were found on RQ values obtained by both metabolic carts (P = 0.642). Absolute inter-day RMR differences obtained with the MGU were higher than those obtained with the CCM (219 ± 185 vs. 158 ± 154 kcal/day, respectively, P = 0.002; 18.3 ± 17.2% vs. 13.5 ± 15.3%, respectively, P = 0.046). We observed a significant positive association of absolute inter-day differences in RMR obtained with both metabolic carts (ß = 0.717; R2 = 0.743; P < 0.001). CONCLUSIONS: The CCM metabolic cart provides lower RMR values and seems more reliable than the MGU in our sample of young adults. Our findings also suggest that a great part of inter-day variability is explained by the individuals.

Correlates of ideal cardiovascular health in European adolescents: The HELENA study.

BACKGROUND AND AIMS: The ideal cardiovascular health (iCVH) construct consists of 4 health behaviors (smoking status, body mass index, physical activity and diet) and 3 health factors (total cholesterol, blood pressure and fasting glucose). A greater number of iCVH components in adolescence are related to better cardiovascular health, but little is known about the correlates of iCVH in adolescents. Thus, the aim of the study was to examine correlates of iCVH in European adolescents. METHODS AND RESULTS: The study comprised 637 European adolescents with complete iCVH data. Participants were part of the Healthy Lifestyle in Europe by Nutrition in Adolescence (HELENA) study, a cross-sectional, multicenter study conducted in 9 different European countries. Correlates investigated were sex and age, family affluence scale, maternal education, geographic location, sleep time, television viewing, duration of pregnancy, birth weight and breastfeeding. Younger adolescents, those whose mothers had medium/high education or those who watched television less than 2 h per day had a greater number of iCVH components compared to those who were older, had a mother with low education or watched television 2 h or more daily (P ≤ 0.01). CONCLUSION: Since in our study older adolescents had worse iCVH than younger adolescents, early promotion of cardiovascular health may be important. Future studies may also investigate the usefulness of limiting television viewing to promote iCVH. Finally, since adolescents of mothers with low education had poorer iCVH, it may be of special interest to tailor public health promotion to adolescents from families with low socioeconomic status.

Dietary fat intake modifies the influence of the FTO rs9939609 polymorphism on adiposity in adolescents: The HELENA cross-sectional study.

BACKGROUND AND AIMS: The fat mass and obesity associated gene (FTO) has been associated with obesity and dietary intake. The aims were: (i) To assess whether energy and macronutrient intakes were different across the FTOrs9939609 genotypes in adolescents, and (ii) to explore whether dietary fat intake modified the association of the rs9939609 polymorphism with adiposity. METHODS AND RESULTS: The FTOrs9939609 polymorphism was genotyped in 652 adolescents (53% females, 14.8 ± 1.2 years, TT = 246, TA = 296, AA = 110). Energy and macronutrient intake were assessed by two non-consecutive 24 h-recalls. Weight, height, waist circumference and skinfold thicknesses were measured and body fat percent was calculated. Energy and macronutrient intake were similar across the FTOrs9939609 genotypes (P > 0.2). There were significant interactions between the FTO polymorphism and fat intake on adiposity estimates (P < 0.05). In adolescents whose fat intake was below 30% (N = 203), the A allele of rs9939609 was not associated with adiposity indices. In contrast, in adolescents whose fat intake was between 30% and 35% of energy (N = 190), the rs9939609 polymorphism was associated with a 1.9% higher body fat per risk allele (95%CI: 0.39, 3.33; P < 0.05), and in those whose fat intake was higher than 35% (N = 259), it was associated with a 2.8% higher body fat per risk allele (95%CI: 1.27, 4.43; P < 0.001). CONCLUSIONS: These findings support the concept that the deleterious effect of the FTOrs9939609 polymorphism on adiposity is exacerbated in adolescents consuming high fat diets. In contrast, the consumption of low fat diets (<30% of energy) may attenuate the genetic predisposition to obesity in risk allele carriers.

The effect of a multidisciplinary intervention program on hepatic adiposity in overweight-obese children: protocol of the EFIGRO study.

BACKGROUND: Non-alcoholic fatty liver disease is the most frequent liver abnormality observed in overweight or obese children and is strongly associated with metabolic syndrome and insulin resistance. OBJECTIVES: (i) To evaluate the effect of a 22-week multidisciplinary intervention program on hepatic fat fraction in overweight or obese children and (ii) to examine the effect of the intervention on cardiometabolic risk factors, self-esteem and well-being. METHODS: A total of 160 children, 9-11 years, will be recruited by pediatricians and randomly assigned to control (N = 80) or intervention (N = 80) groups. The control group will receive a family-based lifestyle and psycho-educational program (2 days/month), while the intervention group will attend the same lifestyle education and psycho-educational program plus the exercise program (3 days/week). The duration of training sessions will be 90 min of exercise, including warm-up, moderate to vigorous aerobic activities, and strength exercises. The primary outcome is the change in hepatic fat fraction (magnetic resonance imaging, MRI). Secondary outcomes include cardiometabolic risk factors such as total adiposity (dual Xray absorptiometry), visceral adiposity (MRI), functional peak aerobic capacity (cardiopulmonary exercise testing), blood pressure, muscular fitness, speed­agility, and fasting blood insulin, glucose, C-reactive protein, alanine aminotransferase, aspartate aminotransferase, gamma glutamyltransferase, lipid profile and psychological measurements (questionnaires). All the measurements will be evaluated at baseline prior to randomization and after the intervention. DISCUSSION: This study will provide insight in the efficacy of a multidisciplinary intervention program including healthy lifestyle education, psycho-education and supervised exercise to reduce hepatic fat and cardiometabolic risk in overweight children.

Liver enzymes and clustering cardiometabolic risk factors in European adolescents: the HELENA study.

OBJECTIVES: This study aimed to explore the associations of liver biomarkers with cardiometabolic risk factors and their clustering, and to provide reference values (percentiles) and cut-off points for liver biomarkers associated with high cardiometabolic risk in European adolescents. METHODS: Alanine aminotransferase (ALT), gamma-glutamyltransferase (GGT), aspartate aminotransferase to ALT ratio (AST/ALT), waist circumference, blood pressure, triglycerides, high-density lipoprotein cholesterol and insulin were measured in 1084 adolescents. We computed a continuous cardiometabolic risk score and defined the high cardiometabolic risk. RESULTS: Higher ALT and GGT and lower AST/ALT were associated with adiposity and with the number of adverse cardiometabolic risk factors (Ps < 0.05). Higher GGT and lower AST/ALT were associated with higher cardiometabolic risk score (Ps < 0.001) in males and females, and ALT only in males (Ps < 0.001). Gender- and age-specific percentiles for liver biomarkers were provided. Receiver operating characteristic analyses showed a significant discriminatory accuracy of AST/ALT in identifying the low/high cardiometabolic risk (Ps < 0.01) and thresholds were provided. CONCLUSIONS: Higher GGT and lower AST/ALT are associated with higher cardiometabolic risk factors and their clustering in male and female European adolescents, whereas the associations of ALT were gender dependent. Our results suggest the usefulness of AST/ALT as a screening test in the assessment of adolescents with high cardiometabolic risk and provide gender- and age-specific thresholds that might be of clinical interest.

Combined influence of healthy diet and active lifestyle on cardiovascular disease risk factors in adolescents.

To investigate the combined influence of diet quality and physical activity on cardiovascular disease (CVD) risk factors in adolescents, adolescents (n = 1513; 12.5-17.5 years) participating in the Healthy Lifestyle in Europe by Nutrition in Adolescence study were studied. Dietary intake was registered using a 24-h recall and a diet quality index was calculated. Physical activity was assessed by accelerometry. Lifestyle groups were computed as: healthy diet and active, unhealthy diet but active, healthy diet but inactive, and unhealthy diet and inactive. CVD risk factor measurements included cardiorespiratory fitness, adiposity indicators, blood lipid profile, blood pressure, and insulin resistance. A CVD risk score was computed. The healthy diet and active group had a healthier cardiorespiratory profile, fat mass index (FMI), triglycerides, and high-density lipoprotein cholesterol (HDL-C) levels and total cholesterol (TC)/HDL-C ratio (all P ≤ 0.05). Overall, active adolescents showed higher cardiorespiratory fitness, lower FMI, TC/HDL-C ratio, and homeostasis model assessment index and healthier blood pressure than their inactive peers with either healthy or unhealthy diet (all P ≤ 0.05). Healthy diet and active group had healthier CVD risk score compared with the inactive groups (all P ≤ 0.02). Thus, a combination of healthy diet and active lifestyle is associated with decreased CVD risk in adolescents. Moreover, an active lifestyle may reduce the adverse consequences of an unhealthy diet.

Determinants of birth size in Northeast Spain.

OBJECTIVE: To update knowledge on determinants of newborn body size in Northeast of Spain considering gestational, parental and socio-cultural variables. METHODS: Cross-sectional assessment of 1442 infants from Aragón (Spain), born at term between March 2009 and March 2010. Obstetric, neonatal, socio-demographic and parental anthropometry data were collected during the first infant scheduled health examination. Hierarchical linear regression models were used to explore associations between newborn anthropometry and included variables. RESULTS: Birth weight was significantly higher in males than in females (130.7 g), when mother did not smoke during pregnancy (126.3 g), in immigrant mothers (113.1 g) and when parity increased (67.1 g per additional birth). Body weight at birth was 16.9 g higher per kg of maternal weight gain during pregnancy, 5.4 g higher per kg of maternal pre-pregnancy weight and 5.1 g higher per cm of maternal height. Birth length was also significantly higher in males than in females (0.87 cm), when mother did not smoke (0.48 cm), in immigrant mothers (0.64 cm), and it was positively associated with parity, maternal anthropometry and paternal height. Newborn anthropometry was not associated with maternal age, educational level or living location. CONCLUSIONS: Independently of gestational age and newborn sex, the main predictors of birth weight and length were maternal pre-pregnancy anthropometry and weight gain during gestation, to smoke during pregnancy, parity and maternal origin. Our results identify potential modifiable factors influencing newborn body size.

Physical activity attenuates the negative effect of low birth weight on leptin levels in European adolescents; the HELENA study.

We examined whether physical activity (PA) influences the association between birth weight and serum leptin in adolescents. The study comprised a total of 538 adolescents (315 girls), aged 12.5-17.49 years, born at term (≥ 37 weeks of gestation). We measured serum leptin levels and time engaged in moderate-vigorous PA (MVPA) by accelerometry. There was an interaction effect between birth weight and meeting the PA recommendations (60 min/day MVPA) on leptin levels in girls (P = 0.023) but not in boys (P = 0.809). Birth weight was negatively associated with leptin levels in girls not meeting the PA recommendations (i.e. more than 60 min/day of MVPA) (ß = -0.096, P = 0.009), whereas no significant association was observed in those meeting the PA recommendations (ß = -0.061, P = 0.433). In conclusion, meeting the PA recommendations may attenuate the negative effect of low birth weight on serum leptin levels in European female adolescents.

Role of socio-cultural factors on changes in fitness and adiposity in youth: a 6-year follow-up study.

BACKGROUND AND AIMS: Optimal cardio-respiratory fitness and adiposity levels are tightly related to health in youth. We analysed changes in fitness and adiposity in young individuals from two countries, and examined the role of maternal education in these changes. METHODS AND RESULTS: A 6-year follow-up study was conducted on 483 Estonian children (9 years) and 466 Swedish children (9-10 years) and adolescents (15 years). Fitness was assessed by a maximal bike test, and total and central adiposity were indirectly estimated by skinfolds (Slaughter's equation for fat mass) and waist circumference. At follow-up, fitness and adiposity had increased in the children cohort (P ≤ 0.001), while small or no change occurred in the adolescent cohort. In the children cohort, Estonian participants had a lower increase in fitness and a higher increase in adiposity (total and central) than Swedish participants. Higher maternal education increased the odds of remaining fit (top quartile) by half and reduced the risk of remaining fat (top quartile) by half; odds ratios = 1.56 (1.00-2.43), 0.50 (0.32-0.77) and 0.61 (0.39-0.94) for fitness, total and central adiposity, respectively. CONCLUSIONS: Our data suggest that the socioeconomic situation of a country might influence key cardiovascular risk factors (fitness and adiposity), being at higher risk for a low-middle income country (Estonia) than a higher income country (Sweden). The findings stress the role of socioeconomic status, particularly maternal education, in the maintenance of healthy fitness and adiposity levels from childhood into later life. Preventive efforts have to be taken from early age.

Association of circulating visfatin concentrations with insulin resistance and low-grade inflammation after dietary energy restriction in Spanish obese non-diabetic women: role of body composition changes.

BACKGROUND AND AIMS: To assess the influence of body composition changes on circulating serum visfatin after following 12 weeks of energy restricted diet intervention. We also examined the possible role of visfatin in glucose metabolism and in obesity-associated low-grade inflammation. METHODS AND RESULTS: A total of 78 obese (BMI 34.0 ± 2.8 kg/m²) women aged 36.7±7 y volunteered to participate in the study. We measured by DXA body fat mass (FM) and lean mass (LM). Fasting serum visfatin, glucose, insulin, adiponectin, leptin, IL-1ß, IL-6, IL-8, TNF-α and CRP concentrations were analyzed before and after the intervention and HOMA and QUIKI indexes were calculated. Mean weight loss 7.7 ± 3.0 kg and HOMA decreased in 24 ± 35%. Serum visfatin concentration change was negatively associated with LM difference (P < 0.05), whereas no significant relationship was observed with FM changes after energy restricted diet intervention. Changes in circulating serum visfatin levels were significantly and inversely associated with HOMA-IR (P < 0.01) and positively with QUICKI index (P < 0.02) after energy restricted diet intervention, regardless of achieved body weight loss. We did not find any significant association between changes in visfatin levels and IL-1ß, IL-6, IL-8, TNF-α and CRP levels after dietary intervention (all P > 0.2). CONCLUSION: Circulating visfatin concentration is associated with sensitivity improvement achieved after energy restricted diet intervention induced weight loss. Furthermore, LM changes could be an influencing factor on visfatin concentrations and consequently, on the improvement of insulin sensitivity after weight loss in obese non-diabetic women. Our findings did not provide any evidence for a role of visfatin increase on low-grade inflammation after weight loss.

Central adiposity in children born small and large for gestational age.

OBJECTIVE: To evaluate body composition differences between children that were born small (SGA) or large for gestational age (LGA) compared with their counterparts born adequate for gestational age (AGA). METHODS: Body composition was assessed in 124 healthy Caucasian children (50% girls) aged 6-10, classified according to their birth weight for gestational age as AGA, SGA and LGA. Fat mass (FM), percentage of FM, lean mass (LM), bone mineral content (BMC) and bone mineral density were measured by dual-energy X-ray absorptiometry (DXA) in the whole body and at different body regions. RESULTS: LM (adjusted for age and sex) and total BMC (adjusted for age, sex and weight) were both significantly higher in LGA children and lower in SGA when compared with those born AGA. After adjustments for height, LM and BMC differences between groups were not significant. In SGA children, truncal (P<0.05) and abdominal fatness (P<0.01) were higher when compared with both AGA and LGA children, after adjustments for age, sex and height. There were no differences in the percentage of total and central FM between children born LGA and AGA. CONCLUSIONS: During childhood, children born SGA had higher central adiposity regardless of their body size. Children born LGA seem to have a higher body size but with harmonic body composition and adequate body fat distribution. Small size for gestational age at birth could programme excess abdominal fat deposition in children, which is a major factor for the clustering of cardiovascular disease risk factors defining the metabolic syndrome.

Insulin sensitivity at childhood predicts changes in total and central adiposity over a 6-year period.

OBJECTIVE: To examine the associations of insulin resistance at childhood with adiposity changes over a 6-year period (from 9 to 15 years) in a sample of 659 Swedish and Estonian children (52.7% girls) participating in the European Youth Heart Study. RESEARCH, DESIGN AND METHODS: We measured weight, height, waist circumference, biceps, triceps, subscapular, suprailiac, and medial calf skinfolds, and we calculated body mass index (BMI), sum of five skinfolds, and body fat percentage. Fasting plasma glucose and insulin were measured and homeostasis model assessment of insulin resistance (HOMA-IR) was calculated. Changes in puberty stage, sex, centre and the corresponding baseline adiposity values were used as confounders in all analysis. RESULTS: HOMA-IR at childhood was significantly and positively associated with changes in BMI (ß=0.265; P=0.024), sum of five skinfolds (ß=0.3445; P=0.003), body fat percentage (ß=1.042; P=0.016) and waist circumference (ß=0.806; P=0.002) from childhood to adolescence. These relationships persisted when overweight children were excluded from the analysis. BMI, sum of five skinfolds, body fat percentage and waist circumference at childhood were not significantly associated with changes in HOMA-IR (P for all >0.1). CONCLUSIONS: These results give further support to the concept that lower insulin sensitivity at childhood may predict subsequent total and central adiposity gain at adolescence. These findings enhance the role of insulin sensitivity as a target of obesity prevention already from the first decades of life.

Preliminary findings on the role of PLIN1 polymorphisms on body composition and energy metabolism response to energy restriction in obese women.

The aim of the present study was to investigate the association of PLIN1 11482G>A (rs894160) and PLIN1 13041A>G (rs2304795) polymorphisms with body composition, energy and substrate metabolism, and the metabolic response to a 12-week energy-restricted diet in obese women. The study comprised a total of seventy-eight obese (BMI 34·0 (SD 2·8) kg/m(2)) women (age 36·7 (SD 7) years). We measured weight, height and waist circumference before and after a 12-week controlled energy-restricted diet intervention. Body fat mass and lean mass were measured by dual-energy X-ray absorptiometry. RMR and lipid oxidation rate were measured by indirect calorimetry. We also analysed fasting plasma glucose, insulin, cholesterol and leptin. Women carrying the 11482A allele had a lower reduction in waist circumference than non-A allele carriers (3·2 (SD 0·5) v. 4·6 (SD 0·6) %, respectively, P = 0·047; P for gene-diet interaction = 0·064). Moreover, women with the 11482A allele had a higher decrease in lipid oxidation rate than non-A allele carriers (58·9 (SD 6·7) v. 31·3 (SD 8·2) %, respectively, P = 0·012; P for gene-diet interaction = 0·004). There was no interaction effect between the 13041A>G polymorphism and diet-induced changes on the outcome variables (all P>0·1). These results confirm and extend previous findings suggesting that the PLIN1 11482G>A polymorphism plays a modulating role on diet-induced changes in body fat and energy metabolism in obese women.

Association between the FTO rs9939609 polymorphism and leptin in European adolescents: a possible link with energy balance control. The HELENA study.

We examined the association between the FTO rs9939609 polymorphism and serum leptin concentrations in adolescents. The FTO rs9939609 polymorphism was genotyped, and fasting serum leptin and insulin were measured in 655 European adolescents (365 females) aged 14.6 ± 1.2 years. We measured weight, height, triceps and subscapular skinfolds and waist circumference, and body fat percentage was calculated. Sex, pubertal status, center, physical activity (accelerometry), total or central adiposity and serum insulin concentrations were entered as confounders in the analyses. The minor A allele of the FTO rs9939609 was significantly associated with higher serum leptin concentrations independently of potential confounders including adiposity (+3.9 ng ml(-1) per risk allele (95% confidence interval: 2.0, 5.9); adjusted P < 0.001). These findings could link the FTO gene with serum leptin and consequently with the control of energy balance. Leptin could be a possible intermediary contributing to the association between the FTO rs9939609 polymorphism and adiposity.

Basal and postprandial substrate oxidation rates in obese women receiving two test meals with different protein content.

BACKGROUND & AIMS: Fuel utilisation and storage in lean and obese subjects seem to be differently affected by the macronutrient distribution intake. The aim of this intervention study was to explore the extent to which the fat mass status and the macronutrient composition of an acute dietary intake influence substrate oxidation rates. METHODS: Fuel utilisation in 26 women, 14 obese (BMI = 37.1 +/- 1.1 kg/m2) and 12 lean (BMI = 20.6 +/- 0.5 kg/m2) was measured over 6 h to compare the metabolic effect of a single balanced protein (HC) meal and a high protein (HP) single meal, which were designed to supply similar energy contents (1672 kJ). The macronutrient composition as a percentage of energy of the HC meal was 55% carbohydrate, 15% protein and 30% fat, while the HP meal contained 40% carbohydrate, 30% protein and 30% fat. Nutrient oxidation rates and energy expenditure were calculated by indirect calorimetry (hood system), whereas exogenous amino acid oxidation was estimated from the 13C isotopic enrichment of breath after oral administration of L[1-13C]leucine. RESULTS: Fasting lipid oxidation was higher in the obese than in the lean women (P < 0.05), and it was significantly correlated with body fatness (P < 0.01). A single HP meal consumption produced higher postprandial fat oxidation as compared with HC meal intake (P < 0.02), in both obese and lean subjects, with no apparent changes in glucose oxidation rates. Furthermore, postprandial fat utilisation after the test meal intake was higher in obese than in the lean women (P < 0.01). The time course of 13CO2 in breath followed a similar pattern in both dietary groups, although a non-statistically significant higher trend in protein and 13C-leucine oxidation was found in the HP group. CONCLUSIONS: Net lipid oxidation depends on both short-term dietary composition intake and fat body mass, being significantly higher after a relatively high protein meal as compared to a balanced diet intake and in obese women as compared to lean controls.