1 Department of Health, Kinesiology, and Applied Physiology, Concordia University, Montreal, Quebec, Canada; Montreal Behavioural Medicine Centre (MBMC), Centre intégré universitaire de santé et de services sociaux du Nord-de-l'Île-de-Montréal (CIUSSS-NIM), Quebec, Canada.
2 Department of Health, Kinesiology, and Applied Physiology, Concordia University, Montreal, Quebec, Canada.
3 School of Nutrition Sciences, University of Ottawa, Ontario, Canada; The Royal's Institute of Mental Health Research, Ottawa, Ontario, Canada.
4 Research centre of the Institut Universitaire de Gériatrie de Montréal (CRIUGM), Centre intégré universitaire de santé et de services sociaux du Centre-Sud-de-l'Île-de-Montréal (CIUSSS-CSMTL), Montreal, Quebec, Canada; Department of Psychology, University of Montreal, Montreal, Quebec, Canada.
5 Faculty of Land and Food Systems, University of British Columbia (UBC), Vancouver, British Columbia, Canada.
6 Division of Bariatric Surgery, CIUSSS-NIM, Montreal, Canada; Department of Surgery, Université de Montréal, Montréal, Canada.
7 Montreal Behavioural Medicine Centre (MBMC), Centre intégré universitaire de santé et de services sociaux du Nord-de-l'Île-de-Montréal (CIUSSS-NIM), Quebec, Canada; Department of Psychology, Université du Québec a Montréal (UQAM), Montreal, Quebec, Canada.
8 Montreal Behavioural Medicine Centre (MBMC), Centre intégré universitaire de santé et de services sociaux du Nord-de-l'Île-de-Montréal (CIUSSS-NIM), Quebec, Canada.
9 Research centre of the Institut Universitaire de Gériatrie de Montréal (CRIUGM), Centre intégré universitaire de santé et de services sociaux du Centre-Sud-de-l'Île-de-Montréal (CIUSSS-CSMTL), Montreal, Quebec, Canada.
10 Department of Medicine, Faculty of Medicine and Health Sciences, McGill University, Montreal, Quebec, Canada; Center for Outcomes Research and Evaluation, Research Institute of the McGill University Health Centre (MUHC), Montreal, Quebec, Canada.
11 Department of Health, Kinesiology, and Applied Physiology, Concordia University, Montreal, Quebec, Canada; Metabolism, Obesity and Nutrition Lab, PERFORM Centre, Concordia University, Montreal, Quebec, Canada; Research Centre, Centre intégré universitaire de santé et de services sociaux du Nord-de-l'Île-de-Montréal (CIUSSS-NIM), Quebec, Canada.
12 Department of Chemistry and Biochemistry, Concordia University, Montreal, Quebec, Canada.
13 Montreal Behavioural Medicine Centre (MBMC), Centre intégré universitaire de santé et de services sociaux du Nord-de-l'Île-de-Montréal (CIUSSS-NIM), Quebec, Canada; Department of Psychology, Concordia University, Montreal, Quebec, Canada.
14 Department of Health, Kinesiology, and Applied Physiology, Concordia University, Montreal, Quebec, Canada; Montreal Behavioural Medicine Centre (MBMC), Centre intégré universitaire de santé et de services sociaux du Nord-de-l'Île-de-Montréal (CIUSSS-NIM), Quebec, Canada. Electronic address: simon.bacon@concordia.ca.

Background: Bariatric surgery leads to profound changes in gut microbiota and dietary patterns, both of which may interact to impact gut-brain communication. Though cognitive function improves postsurgery, there is a large variability in outcomes. How bariatric surgery-induced modifications in the gut microbiota and dietary patterns influence the variability in cognitive function is still unclear.

Objectives: To elucidate the associations between bariatric surgery-induced changes in dietary and gut microbiota patterns with cognition and brain structure.

Setting: University hospital.

Methods: A total of 120 adult patients (=30 years) scheduled to undergo a primary bariatric surgery along with 60 age-, sex-, and body mass index-matched patients on the surgery waitlist will undergo assessments 3-months presurgery and 6- and 12-month postsurgery (or an equivalent time for the waitlist group). Additionally, 60 age-and sex-matched nonbariatric surgery eligible individuals will complete the presurgical assessments only. Evaluations will include sociodemographic and health behavior questionnaires, physiological assessments (anthropometrics, blood-, urine-, and fecal-based measures), neuropsychological cognitive tests, and structural magnetic resonance imaging. Cluster analyses of the dietary and gut microbiota changes will define the various dietary patterns and microbiota profiles, then using repeated measures mixed models, their associations with global cognitive and structural brain alterations will be explored.

Results: The coordinating study site (Centre intégré universitaire de santé et de services sociaux du Nord-de-l'Île-de-Montréal, QC, Canada), provided the primary ethical approval (Research Ethics Board#: MP-32-2022-2412).

Conclusions: The insights generated from this study can be used to develop individually-targeted neurodegenerative disease prevention strategies, as well as providing critical mechanistic information.