Comparison of isotope ratio mass spectrometry and cavity ring-down spectroscopy procedures and precision of the doubly labeled water method in different physiological specimens.

RATIONALE: This study determines if saliva collection procedures for the doubly labeled water (DLW) method, used for measuring total energy expenditure (TEE), are comparable to urine and plasma collection. Both the cavity ring-down spectroscopy (CRDS) and isotope ratio mass spectrometry (IRMS) analyses techniques are compared. METHODS: Saliva specimens were collected from participants for the DLW method. The specimens were collected under different conditions: after consumption of tap water, after chewing gum, and during exposure to conditions of high and low relative humidity. The isotopes in saliva were compared with simultaneous plasma and urine collection. TEE calculated from saliva and analyzed using CRDS was compared to that of plasma analyzed using IRMS. RESULTS: The within-individual variances were not significantly different between the saliva specimens (0.4‰) and plasma (0.3‰). After the oral dose of DLW, the saliva specimens displayed a shorter equilibration time to urine. When participants consumed 500 mL of tap water, the enrichment of saliva specimens reached a new plateau value faster than urine. Saliva collection exposed to high ambient humidity conditions was slightly less enriched as compared to low-humidity conditions while urine enrichment was unaffected. In contrast, whereas the within-individual effects of gum chewing during saliva collection on 18 O were unaffected, the abundance of 2 H in saliva was slightly lower after chewing the gum. The within-individual difference between TEE calculated from saliva and that calculated from plasma analyzed using IRMS did not differ from zero, and the standard deviation was not different from that predicted by a propagation of error analysis based on analytical error alone. CONCLUSIONS: Our findings support using saliva specimens for the DLW method. The analysis of plasma and urine, however, requires reducing the memory effect resulting from contaminants. Also, it should be performed in a manner that minimizes exposure to air where specimens may be exposed to evaporation or contamination from water vapor during sampling.

Accuracy of total energy expenditure predictive equations after a massive weight loss induced by bariatric surgery.

BACKGROUND AND AIMS: Predictive equations remain the clinical tool of choice to estimate the energy expenditure, however, poor accuracy has been found when applied in patients with severe obesity. The aim of this study was to test the accuracy of the total energy expenditure (TEE) those obtained by predictive equations of resting energy expenditure (REE) times individual estimates of metabolic equivalents (MET), taking as reference the TEE measured by doubly labeled water (DLW), before, six and twelve months after bariatric surgery. SUBJECTS AND METHODS: Twenty class III obese women (age: 29.4 ± 5.1 years; BMI: 44.9 ± 2.5 kg/m2), approved for Roux-en-Y gastric bypass participated in this study. TEE and body composition was measured after administration of a fixed dose of DLW. Predictive equations of REE were selected: Dietary Reference Intake (DRI), World Health Organization, Oxford, Harris-Benedict, Mifflin, De Lorenzo, Lazzer and Muller and their collaborators. The MET values were obtained individually by triaxial accelerometer. RESULTS: The patients showed 65% of excess weight loss. The body fat mass decreased 17% after 1 year of surgery. TEE (2930 ± 525 kcal.day-1) decreased by 20% (p < 0.05) by the sixth postoperative month (2319 ± 430 kcal.day-1), increasing 10% by the twelfth month (2538 ± 336 kcal.day-1). The Harris and Benedict (accuracy: 65%) and DRI equations (accuracy: 60%) yielded better results in the prediction of TEE values at pre-surgery. In the sixth month after surgery, only the equation of Harris and Benedict kept accuracy above 50%. At twelve months post-surgery, only the equation of Lazzer et al. considering body composition showed better prediction (accuracy: 50%) in this period. CONCLUSION: None of the prediction equations tested was accurate for estimating TEE for the 3 periods evaluated; however, while there are no reports of specific equations for class III obese women, the Harris and Benedict x MET and DRI equations, can describe the TEE with acceptable accuracy. After surgery, the best equation to be used will depend if the patient has been treated for weight loss and in which post-treatment period it is used. Registration of clinical trial as an observational study in Brazilian Clinical Trials Registry: RBR-8k5jsj. Universal Trial Number: U1111-1206-0858.

Dilution space ratio of 2H and 18O of doubly labeled water method in humans.

Variation of the dilution space ratio (Nd/No) between deuterium ((2)H) and oxygen-18 ((18)O) impacts the calculation of total energy expenditure (TEE) by doubly labeled water (DLW). Our aim was to examine the physiological and methodological sources of variation of Nd/No in humans. We analyzed data from 2,297 humans (0.25-89 yr old). This included the variables Nd/No, total body water, TEE, body mass index (BMI), and percent body fat (%fat). To differentiate between physiologic and methodologic sources of variation, the urine samples from 54 subjects were divided and blinded and analyzed separately, and repeated DLW dosing was performed in an additional 55 participants after 6 mo. Sex, BMI, and %fat did not significantly affect Nd/No, for which the interindividual SD was 0.017. The measurement error from the duplicate urine sample sets was 0.010, and intraindividual SD of Nd/No in repeats experiments was 0.013. An additional SD of 0.008 was contributed by calibration of the DLW dose water. The variation of measured Nd/No in humans was distributed within a small range and measurement error accounted for 68% of this variation. There was no evidence that Nd/No differed with respect to sex, BMI, and age between 1 and 80 yr, and thus use of a constant value is suggested to minimize the effect of stable isotope analysis error on calculation of TEE in the DLW studies in humans. Based on a review of 103 publications, the average dilution space ratio is 1.036 for individuals between 1 and 80 yr of age.

Effect of conjugated linoleic acid on body fat accretion in overweight or obese children.

BACKGROUND: Conjugated linoleic acid (CLA) is a supplemental dietary fatty acid that decreases fat mass accretion in young animals. OBJECTIVE: The aim of this study was to determine CLA's efficacy with regard to change in fat and body mass index (BMI; in kg/m(2)) in children. DESIGN: We conducted a 7 +/- 0.5-mo randomized, double-blind, placebo-controlled trial of CLA in 62 prepubertal children aged 6-10 y who were overweight or obese but otherwise healthy. The subjects were randomly assigned to receive 3 g/d of 80% CLA (50:50 cis-9,trans-11 and trans-10,cis-12 isomers) or placebo in chocolate milk. RESULTS: Fifty-three subjects completed the trial (n = 28 in the CLA group, n = 25 in the placebo group). CLA attenuated the increase in BMI (0.5 +/- 0.8) compared with placebo (1.1 +/- 1.1) (P = 0.05). The percentage change in body fat measured by dual-energy X-ray absorptiometry was smaller (P = 0.001) in the CLA group (-0.5 +/- 2.1%) than in the placebo group (1.3 +/- 1.8%). The change in abdominal body fat as a percentage of total body weight was smaller (P = 0.02) in the CLA group (-0.09 +/- 0.9%) than in the placebo group (0.43 +/- 0.6%). There were no significant changes in plasma glucose, insulin, or LDL cholesterol between groups. Plasma HDL cholesterol decreased significantly more (P = 0.05) in the CLA group (-5.1 +/- 7.3 mg/dL) than in the placebo group (-0.7 +/- 8 mg/dL). Bone mineral accretion was lower (P = 0.04) in the CLA group (0.05 +/- 0.03 kg) than in the placebo group (0.07 +/- 0.03 kg). Reported gastrointestinal symptoms did not differ significantly between groups. CONCLUSIONS: CLA supplementation for 7 +/- 0.5 mo decreased body fatness in 6-10-y-old children who were overweight or obese but did not improve plasma lipids or glucose and decreased HDL more than in the placebo group. Long-term investigation of the safety and efficacy of CLA supplementation in children is recommended.