Introduction: Protein-enriched diets improve glycemic control in diabetes or emotional behavior in depressive patients. In mice, these benefits depend on intestinal gluconeogenesis activation by di/tripeptides. Intestinal di/tripeptides absorption is carried out by the Peptide transporter 1, PEPT1.The lack of PEPT1 might thus alter glucose and emotional balance. Methods:To determine the effects of PEPT1 deficiency under standard dietary conditions or during a dietary challenge known to promote both metabolic and cognitive dysfunction, insulin sensitivity, anxiety and depressive-like traits, hippocampal serotonin (5-HT) and insulin signaling pathway were measured in wild-type (WT) and Pept1 -/-mice fed either a chow or a high-fat high-sucrose (HF-HS) diet. Results: Pept1 -/-mice exhibited slight defects in insulin sensitivity and emotional behavior, which were aggravated by a HF-HS diet. Pept1 -/-mice fed a chow diet had lower hippocampal 5-HT levels and exhibited cerebral insulin resistance under HF-HS diet. These defects were independent of intestinal gluconeogenesis but might be linked to increased plasma amino acids levels. Conclusion: Pept1 -/-mice develop prediabetic and depressive-like traits and could thus be used to develop strategies to prevent or cure both diseases.