Novel progress has been made to understand the adverse pathophysiology in the pancreas of offspring exposed to overnutrition in utero. Our study is the first to evaluate whether the adverse effects of maternal overnutrition on offspring beta-cell function are reversible or preventable through preconception maternal diet interventions. Herein, offspring mice were exposed in utero to one of the following: maternal normal-fat diet (NF group), maternal high-fat diet (HF group) or maternal diet transition from an HF to NF diet 9 weeks before pregnancy (H9N group). Offspring mice were subjected to postweaning HF diet for 12 weeks. HF offspring, but not H9N, displayed glucose intolerance and insulin resistance. HF male offspring had enlarged islet beta-cells with reduced beta-cell density, whereas, H9N male offspring did not show these changes. Co-immunofluorescent (Co-IF) staining of glucose transporter 2 (Glut2) and insulin (Ins) revealed significantly more Glut2(+)Ins(-) cells, indicative of insulin degranulation, in HF male offspring but not H9N. In addition, Co-IF of insulin and p-H3S10 indicated that beta cells of HF male offspring, but not H9N, had proliferation defects likely due to inhibited protein kinase B (AKT) phosphorylation. In summary, our study demonstrates that maternal H9N diet effectively prevents functional deterioration of beta cells seen in HF male offspring by avoiding beta-cell proliferation defects and degranulation. (C) 2020 Elsevier Inc. All rights reserved.