Preventing Gestational Diabetes Mellitus by Improving Healthy Diet and/or Physical Activity during Pregnancy: An Umbrella Review Kouiti, Malak Hernández-Muñiz, Cristian Youlyouz-Marfak, Ibtissam Salcedo Bellido, Inmaculada Mozas Moreno, Juan Jiménez Moleón, José Juan Gestational diabetes mellitus Dietary intervention Physical activity intervention Randomized controlled clinical trials Experimental studies Systematic review Meta-analysis Supplementary Materials: The following are available online at https://www.mdpi.com/article/ 10.3390/nu14102066/s1, Tables S1–S3: Search strategy, Table S4: Excluded studies and justification, Figure S1: Quality of included reviews assessed by Amstar 2, Tables S5–S9: Overlapping assessment, Table S10: Description of physical activity intervention in included systematic reviews, Table S11: Description of diet intervention in included systematic reviews, Table S12: Description of mixed intervention in included systematic review. Acknowledgments: The authors thank Ingrid de Ruiter, MBChB, for English language and editing support. The results of this study are part of the doctoral thesis of Malak Kouiti. Several epidemiological studies have analyzed the effects of lifestyle modification on reducing the risk of gestational diabetes mellitus (GDM); however, their results remain inconsistent. This umbrella review aims to evaluate the effects of diet and/or physical activity interventions during pregnancy on preventing GDM. Systematic reviews and meta-analysis of randomized clinical trials reporting preventive effects of diet and/or physical activity in reducing the incidence of GDM were included from PubMed, Web of Science, Scopus and Cochrane library. Two authors independently assessed the overlapping and quality of the 35 selected reviews using AMSTAR 2. The results, although variable, tend to defend the protective role of diet and physical activity interventions separately and independently of each other in the prevention of GDM. However, the results for the combined interventions show a possible protective effect; however, it is not entirely clear because most of the analyzed meta-analyses tend to approach 1, and heterogeneity cannot be ruled out. Establishing conclusions about the most efficient type of intervention and a dose–effect relationship was not feasible given the low quality of systematic reviews (83% low to critically low) and the variability in reporting interventions. Therefore, more studies with better quality and definition of the interventions are required. The protocol was previously registered in PROSPERO as CRD42021237895. 2022-06-07T12:34:32Z 2022-06-07T12:34:32Z 2022-05-14 journal article Kouiti, M.; Hernández-Muñiz, C.; Youlyouz-Marfak, I.; Salcedo-Bellido, I.; Mozas-Moreno, J.; Jiménez-Moleón, J.J. Preventing Gestational Diabetes Mellitus by Improving Healthy Diet and/or Physical Activity during Pregnancy: An Umbrella Review. Nutrients 2022, 14, 2066. [https://doi.org/10.3390/nu14102066] http://hdl.handle.net/10481/75314 10.3390/nu14102066 eng http://creativecommons.org/licenses/by/3.0/es/ open access Atribución 3.0 España MDPI