Tryptophane (Trp) is an essential amino acid whose metabolic fate is protein synthesis and use in 3 metabolic pathways: Kynurenine (KYN), indoles and serotonin. If Trp deficiencies are known to reduce growth and appetite in monogastrics, less is known on Trp’s fate in overfeeding, when animals develop insulin resistance (IR). In humans, increased levels of Trp and metabolites occur in type 2 diabetes. Our aim is to determine if Trp can mark the onset of IR-related metabolic perturbations and what can be the consequences on Trp requirements in a monogastric model: mice. C57BL/6 mice were fed one month with a control diet (CON) (n=8) or CON diet with 10% starch substituted by fructose (n=8) (FRU). Trp and metabolites (from the 3 pathways) were assayed in arterial serum, jejunum, colon, fecal content and liver (LC-HRMS) in the fasted state. Insulin and glucose were measured in serum (ELISA and enzymatic method). Comparisons between groups: ANOVA, post hoc: Tukey. Although weight gain, intake and serum insulin /glucose were not differentially altered in the two groups, Trp increased (P<0.05, +21.8%) in FRU vs CON as well as KYN, 3-OH-KYN, picolinic acid and KYN/Trp ratio. This suggests a stimulation of KYN pathway by fructose. On the contrary, the indole pathway, controlled by gut microbiota activity, is inhibited in FRU (indole-3-sulfate (-25,6% - P<0,05). Lastly, 5-OH Try, a precursor of serotonin, is increased in FRU (P<0.05) but other are unaltered. The activation of KYN pathway in FRU also occurs in jejunum but not colon for 3-OH KYN and 3-OH Anthranilic acid (P>0.05), suggesting an intense activity of KYN pathway in this tissue. Additionally, quinolinic acid (QA), endproduct of KYN pathway, is increased in feces and liver (P<0.05), preventing an accumulation of QA in blood as QA is neurotoxic. Other pathways are under investigation. We show that Trp’s fate in serum and tissues can be strongly altered during the onset of IR. In fast fattening animals, this altered Trp metabolic fate may occur and should require further investigation.