Non-invasive 13C bicarbonate tracer technique for measuring energy expenditure in men – A pilot study

The oral 13C-bicarbonate technique for determination of energy expenditure in dogs: dietary and environmental factors affecting the respiratory quotient and 13C recovery factor

The oral ¹³C-bicarbonate technique (o¹³CBT) can be used for short-term measurements of CO₂ production (RCO₂) and energy expenditure (EEx). The method relies on appropriate estimates for the respiratory quotient (RQ) and recovery factor (RF) of ¹³C. Four Retriever dogs were included in four experiments to validate the o¹³CBT against indirect calorimetry (IC), and determine RQ and RF; Expt. 1: feeding different protein:fat:carbohydrate ratios [in % of metabolisable energy]: 25:33:42 in a maintenance (Mnt.) diet; 38:26:36 in a high-protein high-fibre (H_Fibre) diet and 27:56:17 in a high-fat (H_Fat) diet, simultaneously with start of measurements (T₀); Expt. 2: the Mnt. diet at T₀ or 4 h postprandial (T₄); Expt. 3: T₄ at different ambient temperatures, 22°C and 15°C; Expt. 4: T₄ after 1 h physical activity. The RCO₂ and EEx were determined from the respiration chamber measurements made simultaneously with IC and the o¹³CBT (o¹³CBT_online), and in Expts. 1 and 2, also on two consecutive days using o¹³CBT with collection of breath into breath bags (o¹³CBT_breathbags). The RQ values obtained at T₀ reflected dietary compositions, with the highest least square mean (LSM) of 0.954  for the Mnt. diet, 0.905 for the H_Fibre and 0.877 for the H_Fat diet (p < 0.05). An increased interval between meal and measurement period decreased RQ significantly (p < 0.05) in Expt. 2, LSM being 0.954 at T₀ and 0.909 at T₄. Ambient temperature (Expt. 3) and physical activity (Expt. 4) did not influence postprandial RQ. The RF values were not significantly affected by diet (Expt. 1). Measurements starting at T₀ (Expt. 2) resulted in higher (p < 0.05) RF values than at T₄ (LSM = 0.971 and 0.836, respectively). The ambient temperatures (Expt. 3) did not influence postprandial RF. However, when dogs were physically active prior to measurements (Expt. 4), RF values (LSM = 1.019) were higher (p < 0.05) than when resting only (LSM = 0.836). Calculations based on RQ and RF determined in each experiment resulted in RCO₂ and EEx values which were not different regardless of method used, except for Expt. 1 where EEx-values [kJ · kg BW^-0.75 · d^-1] were higher (p < 0.05) when measured with o¹³CBT_breathbags (460) than by IC (421) and o¹³CBT_online (420). Provided accurate RQ and RF values, the o¹³CBT_breathbags can be used as an independent and minimally invasive research tool to determine EEx in dogs under carefully standardised conditions.

Estimation of energy expenditure using the oral 13 C-bicarbonate technique in privately owned adult and senior dogs of three different body sizes

Knowledge about energy requirements (ER) of dogs is important in order to provide dogs with an appropriate energy supply. In this study, the oral ¹³ C-bicarbonate technique (o¹³ CBT) was used to estimate energy expenditure (EE) in 50 privately owned dogs of different body sizes (small: Danish-Swedish Farmdog (DSF, n = 16), medium: Beagle (n = 15), large: Labrador Retriever (n = 19)), of different ages (adult: 2-7 years (n = 33), senior: ≥8 years (n = 17)). The aim was to evaluate the feasibility of the method in the field and to get more information about ER of dogs. All dogs were measured twice, on two separate days under standardized, resting conditions. The dogs were fasted overnight prior to measurements, which were carried out in home environment. Only measurements of dogs resting calmly were included in the statistical analyses. No significant difference (p > 0.05) in EE was found between days of measurements. The EE measured in Labrador Retrievers (405 kJ (97 kcal)/kg BW^0.75 /day) was significantly lower (p < 0.001) than of Beagles (530 kJ (127 kcal)/kg BW^0.75 /day) and DSF (497 kJ (119 kcal)/kg BW^0.75 /day), the difference between Beagles and DSF being non-significant. Senior dogs had significantly lower (p < 0.001) EE values than adult dogs with least square means (LSM) of 441 kJ (105 kcal)/kg BW^0.75 /day and 513 kJ (123 kcal)/kg BW^0.75 /day respectively. Analysed within breeds, EE of senior Labrador Retrievers (370 kJ (88 kcal)/kg BW^0.75 /day)) was significantly lower (p < 0.01) than adults (439 kJ (105 kcal)/kg BW^0.75 /day), as well as in DSF (453 kJ (108 kcal)/kg BW^0.75 /day and 541 kJ (129 kcal)/kg BW^0.75 /day for senior and adult dogs respectively). However, the EE was not significantly different (p > 0.05) between adult (548 kJ (131 kcal)/kg BW^0.75 /day) and senior (499 kJ (119 kcal)/kg BW^0.75 /day) Beagles. This study suggests that when measured under standardized resting conditions, the o¹³ CBT can provide reliable results of EE and be a helpful tool to get more knowledge about ER of dogs of different sizes, breeds and ages.

A novel doubly labelled 13C, 15N amino acid method for measuring energy and protein metabolism in man

A novel doubly [1-¹³C, α-¹⁵NH₂]-labelled amino acid method (DLAAM) is presented for the determination of the CO₂ production (RCO₂) and energy expenditure in humans. This method is based on the simultaneous administration of [1-¹³C]glycine and [¹⁵N]glycine followed by the measurement of excretion kinetics of breath ¹³CO₂ and urinary ¹⁵N. The basic idea of the DLAAM is that the unknown ¹³C recovery RF(¹³C) of the 1-¹³C amino acid, essential for the calculation of the net CO₂ production, can be approximated by the easily measureable ¹⁵N recovery RF(¹⁵N) of the α-¹⁵NH₂ labelled amino acid. In four healthy adult men (76-97 kg) the DLAAM was tested parallel to the IC and in one man (74 kg) parallel to the DLWM. Using the approximation RF(¹³C) ≈ RF(¹⁵N) the RCO₂ (in l CO₂ d^-1) was calculated to 387.0 ± 30.3 (DLAAM) vs. 382.8 ± 22.6. (IC). The Bland-Altman plot shows that the difference between the DLAAM and IC of individual RCO₂ is within the 95 % confidence interval (mean ± 2 SD): +4.3 ± 37.5 l CO₂ d^-1. We conclude that the DLAAM and IC may be used interchangeably. The physical activity level (PAL) was calculated based on the DLAAM vs. DLWM to about 1.5.

Fetal over- and undernutrition differentially program thyroid axis adaptability in adult sheep

OBJECTIVE

We aimed to test, whether fetal under- or overnutrition differentially program the thyroid axis with lasting effects on energy metabolism, and if early-life postnatal overnutrition modulates implications of prenatal programming.

DESIGN

Twin-pregnant sheep (n = 36) were either adequately (NORM), under- (LOW; 50% of NORM) or overnourished (HIGH; 150% of energy and 110% of protein requirements) in the last-trimester of gestation. From 3 days-of-age to 6 months-of-age, twin lambs received a conventional (CONV) or an obesogenic, high-carbohydrate high-fat (HCHF) diet. Subgroups were slaughtered at 6-months-of-age. Remaining lambs were fed a low-fat diet until 2½ years-of-age (adulthood).

METHODS

Serum hormone levels were determined at 6 months- and 2½ years-of-age. At 2½ years-of-age, feed intake capacity (intake over 4-h following 72-h fasting) was determined, and an intravenous thyroxine tolerance test (iTTT) was performed, including measurements of heart rate, rectal temperature and energy expenditure (EE).

RESULTS

In the iTTT, the LOW and nutritionally mismatched NORM:HCHF and HIGH:CONV sheep increased serum T₃, T₃:T₄ and T₃:TSH less than NORM:CONV, whereas TSH was decreased less in HIGH, NORM:HCHF and LOW:HCHF. Early postnatal exposure to the HCHF diet decreased basal adult EE in NORM and HIGH, but not LOW, and increased adult feed intake capacity in NORM and LOW, but not HIGH.Conclusions: The iTTT revealed a differential programming of central and peripheral HPT axis function in response to late fetal malnutrition and an early postnatal obesogenic diet, with long-term implications for adult HPT axis adaptability and associated consequences for adiposity risk.

Conjugated linoleic acid does not affect digestion and absorption of fat and starch-a randomized, double-blinded, placebo-controlled parallel study

OBJECTIVE

Conjugated linoleic acid (CLA) is known as a potent agent for altering body weight and composition. However, its effect on the process of digestion is still unknown. The aim of this study has been to elucidate the effect of a 3-month supplementation with CLA on starch and fat digestion and absorption in humans.

APPROACH

The study included 74 obese and overweight adults who were randomized to receive 3.0 g of CLA or sunflower oil as placebo daily for 3 months. Digestion and absorption of fat and starch was assessed using non-invasive breath tests with a stable ¹³C isotope (cumulative percentage dose recovery, CPDR) before and after the supplementation period. To exclude the effect of oxidation, in addition total energy expenditure (TTE) was measured by a ¹³C bicarbonate breath test.

RESULTS

The changes in CPDR values (∆CPDR median 〈interquartile range〉) were no different between subjects from the CLA group and the placebo group (fat: -0.2 〈-9.1-4.1〉 versus 0.6 〈-7.0-8.0〉, p < 0.4796; starch: -1.3 〈-9.5-2.4〉 versus -1.0 〈-5.1-1.7〉, p < 0.5520, respectively). The incidence of negative and positive values of ∆CPDR was no different between groups [for fat: 53.1% versus 46.7%, RR 1.138, (95% CI 0.689-1.882) and for starch: 67.7% versus 56.7%, RR 1.195, (95% CI 0.804-1.777)]. The changes in TTE did not differ between the CLA and the placebo group (respectively 1 〈48; 267〉 versus -8 〈-120;93〉 kcal; p < 0.2728).

CONCLUSION

Supplementation with CLA for 3 months did not affect fat and starch digestion assessed by ¹³C mixed triglyceride breath test and ¹³C starch breath test.

The effect of feeding on CO2 production and energy expenditure in ponies measured by indirect calorimetry and the 13C-bicarbonate technique

Energy expenditure (EE) can be estimated based on respiratory gas exchange measurements, traditionally done in respiration chambers by indirect calorimetry (IC). However, the (13)C-bicarbonate technique ((13)C-BT) might be an alternative minimal invasive method for estimation of CO(2) production and EE in the field. In this study, four Shetland ponies were used to explore the effect of feeding on CO(2) production and EE measured simultaneously by IC and (13)C-BT. The ponies were individually housed in respiration chambers and received either a single oral or intravenous (IV) bolus dose of (13)C-labelled sodium bicarbonate (NaH(13)CO(3)). The ponies were fed haylage 3 h before (T(-3)), simultaneously with (T(0)) or 3 h after (T(+3)) administration of (13)C-bicarbonate. The CO(2) produced and O(2) consumed by the ponies were measured for 6 h with both administration routes of (13)C-bicarbonate at the three different feeding times. Feeding time affected the CO(2) production (P<0.001) and O(2) consumption (P<0.001), but not the respiratory quotient (RQ) measured by IC. The recovery factor (RF) of (13)C in breath CO(2) was affected by feeding time (P<0.01) and three different RF were used in the calculation of CO(2) production measured by 13C-BT. An average RQ was used for the calculations of EE. There was no difference between IC and (13)C-BT for estimation of CO(2) production. An effect of feeding time (P<0.001) on the estimated EE was found, with higher EE when feed was offered (T(0) and T(+3)) compared with when no feed was available (T -3) during measurements. In conclusion, this study showed that feeding time affects the RF and measurements of CO(2) production and EE. This should be considered when the (13)C-BT is used in the field. IV administration of (13)C-bicarbonate is recommended in future studies with horses to avoid complex (13)C enrichment-time curves with maxima and shoulders as observed in several experiments with oral administration of (13)C-bicarbonate.

The oral [(13)C]bicarbonate technique for measurement of short-term energy expenditure of sled dogs and their physiological response to diets with different fat:carbohydrate ratios

The oral [¹³C]bicarbonate technique (o¹³CBT) was assessed for the determination of short-term energy expenditure (EE) under field conditions. A total of eight Alaskan huskies were fed two experimental diets in a cross-over experiment including two periods of 3 weeks. Effects of diets on EE, apparent total tract digestibility (ATTD) and on plasma hormones, blood lactate and glucose were furthermore investigated. The percentages of metabolisable energy derived from protein (P), fat (F) and carbohydrates (C) were 26:58:16 in the PFC diet and 24:75:1 in the PF diet. Measurements of EE were performed in the post-absorptive state during rest. Blood samples were collected during rest and exercise and ATTD was determined after days with rest and with exercise. EE was higher (P < 0·01) in period 2 than in period 1 (68 v. 48 kJ/kg body weight^0·75 per h). The ATTD of organic matter, crude protein and crude fat was higher (P < 0·01) in the PF diet compared with the PFC diet, and lower (P < 0·01) for total carbohydrates. Exercise did not affect ATTD. Higher (P < 0·01) insulin-like growth factor 1 and leptin concentrations were measured when fed the PF diet compared with the PFC diet. Concentrations of insulin decreased (P < 0·01), whereas cortisol and ghrelin increased (P < 0·05), after exercise. There was no effect of diet on blood lactate and glucose, but higher (P < 0·001) lactate concentrations were measured in period 1 than in period 2. The results suggest that the o¹³CBT can be used in the field to estimate short-term EE in dogs during resting conditions. Higher ATTD and energy density of the PF diet may be beneficial when energy requirements are high.

The ¹³C bicarbonate method: an inverse end product method for measuring CO₂ production and energy expenditure

We reconsider the principle of the (13)C bicarbonate (NaH(13)CO3) method ((13)C-BM) for the determination of the CO2 production to obtain an estimate of energy expenditure (EE). Its mathematical concept based on a three-compartmental model is related to the [(15)N]glycine end product method. The CO2 production calculated by the (13)C-BM, RaCO2((13)C) is compared to the result from the indirect calorimetry, RCO2(IC). In an interspecies comparison (dog, goat, horse, cattle, children, adult human; body mass ranging from 15 to 350 kg, resting and fasting conditions) we found an excellent correlation between the results of (13)C-BM and IC with RCO2(IC) = 0.703 × RaCO2((13)C), (R(2) = 0.99). The slope of this correlation corresponds to the fractional (13)C recovery (RF((13)C)) of (13)C in breath CO2 after administration of NaH(13)CO3. Significant increase in RF((13)C) was found in physically active dogs (0.95 ± 0.14; n = 5) vs. resting dogs (0.71 ± 0.10, n = 17; p = .015). The (13)C recovery in young bulls was greater in blood CO2 (0.81 ± 0.05) vs. breath CO2 (0.73 ± 0.05, n = 12, p < .001) and in ponies with oral (0.76 ± 0.03, n = 8) vs. intravenous administration of NaH(13)CO3 (0.69 ± 0.07; n = 8; p = .026). We suggest considering the (13)C-BM as a 'stand-alone' method to provide information on the total CO2 production as an index of EE.

Evaluation of the oral (13)C-bicarbonate technique for measurements of energy expenditure in dogs before and after body weight reduction

BACKGROUND

Overweight and obesity are the most common nutritional disorders in dogs and may lead to various secondary diseases and decreased lifespan. In obesity research, measurement of energy expenditure (EE) and determination of the energy requirements are essential. The objective with this study was to validate and evaluate the suitability of the oral (13)C-bicarbonate technique (o(13)CBT) for measuring EE in dog obesity studies. A further objective was to investigate the impact of body weight (BW) reduction and changes in body composition on the EE when measured under conditions corresponding to the basal metabolic rate (BMR).

RESULTS

The EE in five privately owned, overweight dogs was measured simultaneously with the o(13)CBT and indirect calorimetry (IC) for comparison of the results. Two measurements per dog were performed under the same standardised conditions (i.e. fasted and resting state) at the start, and after completing a 12-week BW reduction program. Additionally, measurements of body composition by Dual-energy X-ray absorptiometry (DEXA) were conducted at the beginning and at the end of the BW reduction program. There were no differences in EE results obtained by the o(13)CBT and IC. Overweight and the BW reduction did not affect the estimates for the respiratory quotient (RQ) or the recovery factor for the (13)C-tracer (RF), both needed when using the o(13)CBT. The dogs lost 16% (SD ± 2.0) of their initial BW in reduced fat mass (P < 0.001), whereas fat free mass (FFM) remained unchanged. There was no effect of the BW reduction on the determined EE expressed in kJ/kg BW/d, or in kJ/kg BW(0.75)/d. However, EE was lower (P < 0.001) after the BW reduction program when expressed in relation to FFM (kJ/kg FFM/d).

CONCLUSIONS

Results from the present study show that the o(13)CBT can be a used in obesity research to determine EE in fasted dogs and under resting conditions. Furthermore, the results suggest that the BMR does not change with reduced BW in overweight dogs as long as the FFM remains unchanged. This indicates that the BMR to maintain one gram of fat is equal to maintaining one gram of FFM in overweight dogs.

A prospective randomised study comparing oral 13C-bicarbonate tracer technique versus indirect calorimetry for measurement of energy expenditure in adults

BACKGROUND AND AIMS

Accurate assessment of energy expenditure (EE) is important in guiding nutritional therapy but current methods are unsatisfactory. This study compared the oral ¹³C-bicarbonate tracer (BT) technique using the IRIS® system (Wagner, Germany) against indirect calorimetry (IC, ventilated-hood) to measure CO₂ output (VCO₂) and thus estimate EE.

METHODS

Ten overnight-fasted healthy male volunteers were randomised to studies at rest or mild exercise in a crossover manner. During each study BT-IRIS® and IC were used simultaneously to measure VCO₂ and thus EE. Participants ingested a drink labelled with 50mg ¹³C-bicarbonate and breath samples were collected every 5 min for 180 min and analysed using IRIS®. Bland-Altman plots were used to assess agreement between the two techniques in measurements of VCO₂ (L/day) and estimates of EE (kJ/day).

RESULTS

Mean ± SE age and BMI of participants were 21.1 ± 1.1 yrs and 23.6 ± 0.6 kg/m². Both at rest and exercise, there was small bias but overall poor agreement between the two techniques as evident by the wide 95% limits of agreement in measurements of VCO₂ and EE: rest VCO₂ (bias 1.4, SD 93, 95% limits of agreement -180 to 183), rest EE (-8.3, 1830, -3595 to 3578), exercise VCO₂ (49.3, 66.1, -80.4 to 178.9) and exercise EE (1083, 1944, -2727 to 4893). Furthermore, there was also evidence of systematic error in these measurements.

CONCLUSION

Prior to clinical application, further optimisation of the BT-IRIS® system should be undertaken, given the poor agreement with IC in measuring VCO₂ and estimating EE.

Evaluation of the oral ¹³C-bicarbonate tracer technique for the estimation of CO₂ production and energy expenditure in dogs during rest and physical activity

For feeding of working dogs during their daily life, illness, routine jobs or sporting activities, an accurate determination of their nutritional requirements is essential to ensure their optimal health and performance. To predict the appropriate guidelines about how to feed dogs, it appears essential to determine the energy expenditure (EE) in a reliable and feasible way. In the present experiment, the non-invasive oral ¹³C-bicarbonate tracer technique (o¹³CT), i.e. collection of breath samples after oral administration of NaH¹³CO₃, was used for the estimation of CO₂ production and EE in dogs. Measurements were conducted during two days of rest, and during three days with 3 h of exercise per day. Average EE was 483 and 876 kJ kg⁻⁰·⁷⁵ d⁻¹ during rest and exercise, respectively. The o¹³CT seems appropriate to use as a minimal restrictive and non-invasive method to obtain reliable estimates of EE in dogs at different activity levels under near natural conditions.