Introduction: To assess the association of medical nutrition therapy (MNT) consultations and eating behavior with gestational weight gain (GWG) in Mexican women with type 2 diabetes mellitus (T2DM) and gestational diabetes mellitus (GDM). Material and methods: Cross-sectional study conducted at (Blinded for Review) from 2013 to 2014. Fifty-seven patients with T2DM or GDM were invited to participate. The dependent variable was GWG and the main independent variables were MNT and eating behaviors. Data were obtained from medical records or interviews. Multiple linear regression models were used to assess associations. Results: Per each additional MNT consultation, GWG was reduced by 1.2 kg (β = −1.2; 95% CI: −2, −0.3; p = .007). After adjusting for age, in women with normal pregestational weight, for each unit, increase in the EE behavior index, there was a GWG increase of 2.8 kg (β = 2.8; 95% CI: 1.2, 4.4; p = .003). Conclusions: This study reinforces the need for additional research to determine how eating behaviors are related to GWG during pregnancy.The authors would like to thank the PH-LEADER program for their support to this research. Research reported in this publication was supported by the Fogarty International Center of the National Institutes of Health (NIH) under Award Number D43TW009135, and by the IRB of the National Institute of Public Health in Mexico.