Association of plant-based dietary patterns in first trimester of pregnancy with gestational weight gain: results from a prospective birth cohort.

Background/objectives: Plant-based dietary patterns are becoming more popular worldwide. We aimed to examine the relationship between plant-based dietary patterns and the risk of inadequate or excessive gestational weight gain (GWG) in Iranian pregnant women.

Methods: We prospectively followed 657 pregnant women in Iran. Adherence to the plant-based diet, represented by plant-based (PDI), healthy (hPDI) and unhealthy plant-based (uPDI) dietary indexes was evaluated by applying a 90-item food frequency questionnaire during the first trimester of pregnancy. Multivariable-adjusted Cox proportional-hazards regression model was used to compute hazard ratios (HRs) and 95% confidence intervals (CIs) across quartiles of plant-based diet scores.

Results: Over 25,562 person-weeks of follow-up, we documented 106 and 294 participants with inadequate and excessive GWG, respectively. We found a strong inverse association between adherence to the PDI and inadequate GWG after adjustment for demographic and confounding variables. Women in the highest quartile of the PDI had 50% lower risk of inadequate GWG than those in the lowest quartile (adjusted HR: 0.50; 95%CI 0.29, 0.89; P = 0.02). No significant association was found between hPDI and uPDI and inadequate GWG. There was no association between PDI, hPDI, and uPDI and the risk of excessive GWG.

Conclusions: Greater adherence to a plant-based diet during the first trimester of pregnancy may be associated with a lower risk of inadequate GWG. This finding needs to be confirmed in larger cohort studies, considering other pregnancy outcomes such as birth weight and the potential changes across the trimester in terms of food types and quantity.