Doubly labelled water: Multi-point and two-point methods in pre-school children.

OBJECTIVE: We compared the multi-sample and two-sample methods for measuring total energy expenditure (TEE) using doubly labelled water (DLW) in pre-school children to establish whether taking multiple samples provides any advantage in free-living conditions. METHODS: Sixty-five children (32 boys; aged 2-6 years) were recruited from Aberdeen, UK. TEE was measured over 7 and 14 days using the multi-point and two-point methods by DLW. Total body composition was measured using dual-energy X-ray absorptiometry. RESULTS: There was no significant difference between the mean TEE estimated using the multi-point and two-point methods. Independent of sampling technique, there was no significant difference in the TEE estimated over 7 and 14 days. Correlation of the deviations of the day-to-day enrichments suggests that the major factors driving isotope affected both isotopes. Association between fat-free mass (FFM) and TEE over 14 days was higher when using the multi-point method (r(2)=57.7%, P<0.001) compared with the two-point method (r(2)=41.1%, P < 0.001). There was no systematic bias in the difference between the two methods. CONCLUSIONS: Multi- and two-point approaches give similar results for calculation of daily TEE in pre-school children. For studies aiming to establish a population level of TEE the two-sample method is a cost effective approach. However, the multi-point method appears to have greater accuracy and precision based on the better relationship to FFM (or FFM and FM combined). Consequently where maximum precision is required, in particular when energy expenditure of individual subjects is needed, this approach may be more appropriate.

The effect of rate and extent of weight loss on urea salvage in obese male subjects.

It is well established that in human subjects a proportion of urea production undergoes hydrolysis in the gastrointestinal tract with release of N potentially available for amino acid synthesis. Previous studies have suggested adaptive changes in urea kinetics, with more urea-N retained within the metabolic pool during reduced dietary intakes of energy and protein. We therefore investigated the effect of rate and extent of weight loss on adaptive changes in urea kinetics in two groups (each n 6) of obese men (mean age 43 (sd 12) years, BMI 34.8 (sd 2.9) kg/m(2)) during either total starvation for 6 d or a very-low-energy diet (2.55 MJ/d) for 21 d. Subjects were resident in the Human Nutrition Unit of the Rowett Research Institute (Aberdeen, Scotland, UK) and lost 6 and 9 % initial body weight within the starvation and dieting groups respectively. Changes in urea-N metabolism were assessed by stable isotope tracer kinetics using [(15)N(15)N]urea infused intravenously for 36 h before, during and after weight loss. In response to weight loss, urea production decreased (P<0.01) by 25 % from 278 to 206 micromol urea-N/h per kg within the dieting group only. However, no changes were observed in the proportion of urea being hydrolysed in the gastrointestinal tract (range 20-25 %) or in the proportion of N retained for anabolic purposes (80-85 % urea-N from gastrointestinal hydrolysis) within either group. It was concluded that no adaptive changes in urea kinetics occurred in response to either the different rate or extent of weight loss.