Respiratory Quotient During Pregnancy and the Influence of Macronutrient Intake, Energy Balance and Maternal Fat Mass: An Exploratory Study.

INTRODUCTION

Maternal metabolism shifts during pregnancy to support foetal growth and development. Respiratory quotient (RQ) provides insight into the relative contributions of carbohydrate and fat to energy metabolism and is influenced by factors including individual macronutrient intake, energy balance, and fat mass. This study aimed to assess the associations between dietary intake, energy balance, and maternal fat mass with RQ and substrate oxidation in pregnant women.

METHODS

Pregnant women in their first trimester were included. At each trimester (First: 8-13 weeks'; Second: 23-25 weeks'; Third: 34-37 weeks'), macronutrient intake was assessed using a 3-day weighed food diary, with RQ and substrate oxidation measured using indirect calorimetry. Maternal fat mass was measured using bioelectrical impedance analysis.

RESULTS

Twenty-seven women were included. The mean (SD) age of women was 33.3 (5.1) years and mean (SD) pre-pregnancy BMI was 26.4 (5.0) kg/m2. Macronutrient intake, RQ, and relative substrate oxidation were unchanged across pregnancy. Pregnant women were in a negative energy balance throughout pregnancy and gained a mean (SD) 4.78 (3.36) kg of fat mass over pregnancy. The RQ value was positively associated with energy balance (β = 8.887 × 10-6, p = 0.017). Maternal fat mass was negatively associated with RQ (β = -0.002, p = 0.016). Macronutrient intake was associated with substrate oxidation.

CONCLUSION

Stable macronutrient intake may influence RQ and substrate oxidation. Larger, adequately powered studies are needed to determine whether more pronounced dietary or body composition changes alter substrate oxidation during pregnancy.