Respiratory quotient evolution during normal pregnancy: what nutritional or clinical information can we get out of it?

Effects of Low Protein-High Carbohydrate Diet during Early and Late Pregnancy on Respiratory Quotient and Visceral Adiposity

Background

Low Protein-High Carbohydrate (LPHC) diet during pregnancy is considered a nutritional and health problem related to the development of maternal metabolic alterations, such as fatty liver and obesity in the perinatal and postnatal period. It is known that increase in visceral adiposity tissue (VAT) modulates maternal metabolic rate, with the respiratory quotient (RQ) being a parameter related to that variable; however, it is unknown whether LPHC intake during pregnancy affects the VAT and the RQ. In this study, we examine if consumption of LPHC during pregnancy modifies the VAT and RQ in early and late periods of pregnancy.

Methods

This is a longitudinal and cross-sectional study with Wistar rats during gestation (G) (3, 8, 15, and 20) and nonpregnant rats. Rats were fed with a control diet with 63/18% carbohydrate/protein and an experimental diet with 79/6% carbohydrate/protein. We studied water and food consumption and metabolic parameters such as RQ and energy expenditure (EE), calculated by indirect calorimetry. In the cross-sectional study, we determined visceral fat, as well as the concentration of free fatty acids, insulin, glucose, and lipid profile in serum.

Results

Nonpregnant rats with LPHC intake decreased significantly in VAT (86%) and the RQ (18%); in pregnant rats in early (8G) and late pregnancy (15G) in LPHC diet, both parameters (VAT and RQ) (25%-92%) increased during light time. When comparing time points during pregnancy in the control and LPHC groups, the RQ increased in 15G during daytime compared to 8G during the night period (17 and 5%, respectively). In late pregnancy, LPHC intake and triacylglyceride levels increased and cholesterol and glucose decreased (45 and 26%, respectively), in comparison to nonpregnant rats.

Conclusions

LPHC intake in nonpregnant rats decreases the RQ and VAT. Interestingly, the opposite occurs in early pregnancy: the RQ and VAT increased, and this correlates with free fatty acid (FFA) levels. The increase in RQ and VAT during light time in early pregnancy increased mobilization of carbohydrate and protein metabolism. These results suggest that LPHC intake during pregnancy increases the glucose metabolism as a compensatory mechanism for energy needs in the fetus and the mother in early pregnancy.

Blood Flow and Respiratory Gas Exchange in the Human Placenta at Term: A Data Update

Reliable measurements using modern techniques and consensus in experimental design have enabled the assessment of novel data sets for normal maternal and foetal respiratory physiology at term. These data sets include (a) principal factors affecting placental gas transfer, e.g., maternal blood flow through the intervillous space (IVS) (500 mL/min) and foeto-placental blood flow (480 mL/min), and (b) O₂, CO₂ and pH levels in the materno-placental and foeto-placental circulation. According to these data, the foetus is adapted to hypoxaemic hypoxia. Despite flat oxygen partial pressure (pO₂) gradients between the blood of the IVS and the umbilical arteries of the foetus, adequate O₂ delivery to the foetus is maintained by the higher O₂ affinity of the foetal blood, high foetal haemoglobin (HbF) concentrations, the Bohr effect, the double-Bohr effect, and high foeto-placental (=umbilical) blood flow. Again, despite flat gradients, adequate CO₂ removal from the foetus is maintained by a high diffusion capacity, high foeto-placental blood flow, the Haldane effect, and the double-Haldane effect. Placental respiratory gas exchange is perfusion-limited, rather than diffusion-limited, i.e., O₂ uptake depends on O₂ delivery.

TIMER: A Clinical Study of Energy Restriction in Women with Gestational Diabetes Mellitus

Medical nutrition therapy is an integral part of gestational diabetes mellitus (GDM) management; however, the prescription of optimal energy intake is often a difficult task due to the limited available evidence. The present pilot, feasibility, parallel, open-label and non-randomized study aimed to evaluate the effect of a very low energy diet (VLED, 1600 kcal/day), or a low energy diet (LED, 1800 kcal/day), with or without personalized exercise sessions, among women with GDM in singleton pregnancies. A total of 43 women were allocated to one of four interventions at GDM diagnosis: (1) VLED (n = 15), (2) VLED + exercise (n = 4), (3) LED (n = 16) or (4) LED + exercise (n = 8). Primary outcomes were gestational weight gain (GWG), infant birth weight, complications at delivery and a composite outcomes score. Secondary outcomes included type of delivery, prematurity, small- for-gestational-age (SGA) or large-for-gestational-age (LGA) infants, macrosomia, Apgar score, insulin use, depression, respiratory quotient (RQ), resting metabolic rate (RMR) and middle-upper arm circumference (MUAC). GWG differed between intervention groups (LED median: 12.0 kg; VLED: 5.9 kg). No differences were noted in the type of delivery, infant birth weight, composite score, prevalence of prematurity, depression, RQ, Apgar score, MUAC, or insulin use among the four groups. Regarding components of the composite score, most infants (88.4%) were appropriate-for-gestational age (AGA) and born at a gestational age of 37-42 weeks (95.3%). With respect to the mothers, 9.3% experienced complications at delivery, with the majority being allocated at the VLED + exercise arm (p < 0.03). The composite score was low (range 0-2.5) for all mother-infant pairs, indicating a "risk-free" pregnancy outcome. The results indicate that adherence to a LED or VLED induces similar maternal, infant and obstetrics outcomes.

Energy expenditure during pregnancy: a systematic review

CONTEXT

Contrary to nutritional guidelines, accumulating evidence shows that pregnant women's energy intakes remain stable throughout trimesters. Although pregnant women may eat below their needs or underreport their energy intakes, it is also relevant to question how energy requirements - estimated through measurements of energy expenditure (EE) - change throughout pregnancy.

OBJECTIVE

This review examined prospective studies that measured EE during pregnancy, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.

DATA SOURCES

PubMed/MEDLINE, Web of Science, Embase, and CINAHL databases were searched to identify relevant publications up to November 14, 2019.

STUDY SELECTION

All studies that measured EE prospectively and objectively during pregnancy were included in this systematic review. Two authors independently screened 4852 references. A total of 32 studies were included in the final analysis.

DATA EXTRACTION

One author extracted data and assessed the risk of bias and a second author did so for a random sample of studies (n = 7; 22%).

DATA ANALYSIS

Increases in resting EE ranged from 0.5% to 18.3% (8-239 kcal), from 3.0% to 24.1% (45-327 kcal), and from 6.4% to 29.6% (93-416 kcal) between early and mid-, mid- and late, and early and late pregnancy, respectively. Increases in total EE ranged from 4.0% to 17.7% (84-363 kcal), from 0.2% to 30.2% (5-694 kcal), and from 7.9% to 33.2% (179-682 kcal) between early and mid-, mid- and late, and early and late pregnancy, respectively. Participants were mainly of normal weight, although many studies did not report important covariates such as prepregnancy body mass index and gestational weight gain adequacy.

CONCLUSIONS

Additional high-quality longitudinal studies (ie, with multiple objective measurements of EE in all periods of pregnancy while considering important confounding variables, like gestational weight gain) are required.

iHWG-MOX: A Hybrid Breath Analysis System via the Combination of Substrate-Integrated Hollow Waveguide Infrared Spectroscopy with Metal Oxide Gas Sensors

According to their materials and operating parameters, metal oxide (MOX) sensors respond to target gases only by a change in sensor resistance with a lack in selectivity. By the use of infrared spectroscopy, highly discriminatory information from samples at a molecular level can be obtained and the selectivity can be enhanced. A low-volume gas cell was developed for a commercially available semiconducting MOX methane gas sensor and coupled directly to a mid-infrared gas sensor based on substrate-integrated hollow waveguide (iHWG) technology combined with a Fourier transform infrared spectrometer. This study demonstrates a sensing process with combined orthogonal sensors for fast, time-resolved, and synergic detection of methane and carbon dioxide in gas samples.

Assessment of Metabolic and Nutritional Imbalance in Mechanically Ventilated Multiple Trauma Patients: From Molecular to Clinical Outcomes

The critically ill polytrauma patient is characterized by a series of metabolic changes induced by inflammation, oxidative stress, sepsis, and primary trauma, as well as associated secondary injuries associated. Metabolic and nutritional dysfunction in the critically ill patient is a complex series of imbalances of biochemical and genetic pathways, as well as the interconnection between them. Therefore, the equation changes in comparison to other critical patients or to healthy individuals, in which cases, mathematical equations can be successfully used to predict the energy requirements. Recent studies have shown that indirect calorimetry is one of the most accurate methods for determining the energy requirements in intubated and mechanically ventilated patients. Current research is oriented towards an individualized therapy depending on the energy consumption (kcal/day) of each patient that also takes into account the clinical dynamics. By using indirect calorimetry, one can measure, in real time, both oxygen consumption and carbon dioxide production. Energy requirements (kcal/day) and the respiratory quotient (RQ) can be determined in real time by integrating these dynamic parameters into electronic algorithms. In this manner, nutritional therapy becomes personalized and caters to the patients’ individual needs, helping patients receive the energy substrates they need at each clinically specific time of treatment.

Gender-specific considerations in physical activity, thermogenesis and fat oxidation: implications for obesity management

With current 'one-size-fits-all' obesity prevention and management strategies proving largely ineffective, the focus has shifted towards a more tailored, individualized approach. However, investigation of the mechanisms underlying inter-individual variability in metabolic profile and response to intervention often yield conflicting results. Indeed, it is perhaps surprising that despite at least a century of recognition that sex hormones influence metabolism, firm conclusions regarding the effects of the menstrual cycle, hormonal contraception and menopause on many aspects of energy expenditure and substrate utilization remain to be drawn. In this review, we examine current evidence relating to gender-specific considerations in the promotion of physical activity, thermogenesis and fat oxidation for body-weight regulation, including the relationship between sex hormone status and non-exercise activity thermogenesis - an energy expenditure compartment that is often overlooked in favour of traditional exercise/sport physical activities yet presents a viable target in the search for effective weight management.

Relationship between gait kinematics and walking energy expenditure during pregnancy in South African women

Background

Various musculoskeletal changes occurring during pregnancy may lead to the change in gait and contribute to the increase in walking energy expenditure. Previous research indicates that changes in gait mechanics may lead to the increase in mechanical work required during walking. However, there is little information to indicate if changes in gait mechanics during pregnancy have impact on active or total energy expenditure. Therefore, the primary aim of this study was to investigate the relationship between changes in gait kinematics and walking energy expenditure in pregnant women.

Methods

Thirty-five women (mean age = 27.5 ± 6.1 years) volunteered for the study during various stages of pregnancy (1st trimester average = 12.1 ± 2.2 weeks; 2nd trimester = 22.3 ± 2.6 weeks; 3rd trimester = 31.4 ± 2.6 weeks). 3D motion analysis was used to assess changes in kinematic parameters during walking at self-selected pace. Resting metabolic rate, and walking energy expenditure expressed in terms of rate and cost of O₂ were analysed with portable metabolic analyser.

Results

Only medio-lateral deviation of centre of gravity (COG_ML) increased 13.6% between the 1st and 2nd, and 39.3% between 2nd and 3rd trimester (p ≤ 0.001). However, self-selected walking speed depicted strong significant positive linear relationship with net O₂ rate (r = 0.70; p ≤ 0.001), and was strongly associated with the vertical excursion of the COG (r = 0.75, p ≤ 0.001).

Conclusions

Changes in gait mechanics during pregnancy may lead to an increase in walking energy expenditure. However, the consequent increase in walking energy cost may not be sufficient to offset the natural energy sparing mechanism.

Prepregnancy body mass index influences lipid oxidation rate during pregnancy

INTRODUCTION

The influence of maternal body mass index (BMI) on respiratory quotient during pregnancy is not clear. We aim to evaluate longitudinal changes in energy expenditure, respiratory quotient, and substrate oxidation rates in normal and overweight women with uncomplicated pregnancies. We hypothesized that the threshold period in switching from a predominantly carbohydrate to a predominantly lipid metabolism may be different in normal and overweight women.

MATERIAL AND METHODS

Forty healthy pregnant women were recruited for a prospective cohort study. They were divided into two groups, normal and overweight (BMI <25 kg/m² or ≥25 kg/m² ). Comparisons of indirect calorimetry data were performed monthly throughout pregnancy. The relationships between energy and substrate metabolism variables and maternal BMI were also analyzed.

RESULTS

There was a significant increase in oxygen consumption (Vo₂ ), carbon dioxide production (Vco₂ ) and resting energy expenditure during pregnancy in both normal and overweight women. In the normal weight group, respiratory quotient decreased during the second trimester and increased in the last trimester. Respiratory quotient was lower in the overweight group in the second trimester and decreased in the last trimester; between-group differences being significant at 20 and 36 weeks (0.85 ± 0.06 vs. 0.81 ± 0.01, p = 0.009; 0.87 ± 0.05 vs. 0.80 ± 0.03, p = 0.01, respectively). Lipid oxidation was significantly higher in overweight women at both 20 and 36 weeks (36.8 ± 19.7% vs. 55.2 ± 5.6%, p = 0.003 and 33.6 ± 18.2% vs. 59.6 ± 12.7%, p = 0.007, for normal and overweight group, respectively).

CONCLUSION

Prepregnancy maternal BMI influences lipid oxidation rate and respiratory quotient during pregnancy.

Algorithm to improve accuracy of energy expended in a room calorimeter

The whole-room indirect calorimeter is considered as important equipment for human energy expenditure measurement, but noise reduction in the system remains a challenge. A selective filtering method (SFM) was designed to improve the accuracy of the computation of O₂ consumption rate ([Formula: see text]) and CO₂ production rate ([Formula: see text]), based on two facts: (1) the rapid changes of [Formula: see text], [Formula: see text] and respiratory quotient (RQ) in human should be accompanied by physical activity; (2) the oxygen consumption and the carbon dioxide production should not be negative because living humans do not generate oxygen, nor consume carbon dioxide. The performance of SFM was compared with the moving average method, the central difference method and the wavelet de-noising method. The range of [Formula: see text] and [Formula: see text] in the empty room (the background noise) is reduced from -130.00-146.00 ml/min to -26.00-24.00 ml/min, and from -20.50-12.50 ml/min to -3.99-4.19 ml/min, by SFM. The background noise was added to simulated rectangular and sinusoidal signals that were used to evaluate the four methods over different time periods (64, 32, 16 and 8 min). The highest signal-to-noise ratio and the lowest deviation were achieved by SFM. Abnormal metabolic rates and RQs were corrected and compensated with measurement accuracy of 98.51 ± 0.3 % for 24-h alcohol burning tests. The results of the study showed that SFM can significantly improve [Formula: see text] and [Formula: see text] measurements.

Fasting substrate oxidation at rest assessed by indirect calorimetry: is prior dietary macronutrient level and composition a confounder?

Indirect calorimetry, the measurement of O₂ consumption and CO₂ production, constitutes an invaluable tool as the most common method for analyzing whole-body energy expenditure, and also provides an index of the nature of macronutrient substrate oxidation--namely, carbohydrate (CHO) versus fat oxidation. The latter constitutes a key etiological factor in obesity as this condition can only develop when total fat oxidation is chronically lower than total exogenous fat intake. The standardization of indirect calorimetry measurements is essential for accurately tracking the relative proportion of energy expenditure derived from CHO and fat oxidation. Here we analyze literature data to show that the average fasting respiratory quotient typically shifts from approximately 0.80 to 0.90 (indicating a doubling of resting CHO oxidation) in response to a switch in dietary CHO intake (as % energy) from 30 to 60%. This underscores the importance of taking into account dietary macronutrient composition prior to indirect calorimetry studies in the interpretation of data on substrate utilization and oxidation.