The NutriNet-Santé Study is a French web-based prospective cohort study on relationships between nutrition and health outcome. Firstly, on subjects of this cohort, we studied the relationship between mood, assessed by 2 repeated Center for Epidemiological Studies Depression Scales (CES-D) questionnaires, and dietary intakes. We selected 1554 participants based on the following inclusion criteria: female, aged 45-60 years, with urinary samples available in the cohort biobank. Statistical analysis showed a positive association between the risk of poor mood (score <17) and meat consumption but no association between dietary fibre consumption and mood. Secondly, since in a previous experiment in rats we had shown that indole production from tryptophane by intestinal microbiota induced anxiety and depression-like behaviours, we undertook to analyse indoxylsulfate, the major detoxification metabolite of indole, in the urine of the selected participants. First results obtained on a subset of 140 samples indicate that the urinary concentrations of indoxylsulfate increase with meat consumption and decrease with dietary fibre consumption. They also tend to be higher in women with a poor mood. If these results were confirmed they would indicate that the relationship between meat consumption and mood involve the microbiota, and more particularly a bacterial metabolite, the indole