The consumption of an adequate quantity of protein in the diet is essential to maintain a healthy body composition and functioning. It is also well established that all proteins are not equal regarding their ability to promote health benefits. Recently, we have innovated in that matter by showing that under the context of high intake of dietary fat, the dairy protein casein was more effective than a mix of proteins representative of a western diet to prevent body weight gain and insulin resistance. This was explained in part by modifications of the gut microbiota. This finding represents the main conceptual basis of the present research program that is aimed to determine the impact of dairy protein from yogurt compared to a plant-based equivalent on body composition indicators including muscle mass and bone mineral density, in relation to the profile of the gut microbiota, the production of newly discovered protein-derived metabolites, and markers of metabolic health. This program will include a human and an animal component requiring the testing of these variables before and after a standardized intervention. The human component will be a clinical study consisting of a 12-week diet-based weight loss intervention in postmenopausal overweight women being randomly assigned to one of the three following groups: yogurt, plant-based yogurt, or kept on diet without supplements. The animal experimentation will permit to causally determine the implication of the gut microbiota in the protein effects following transfer of the human bacteria to germ free mice and validate the benefits seen in humans. It is anticipated that these two complementary investigative approaches will allow a thorough documentation of the impact of fermented dairy protein on body composition and functioning, a better understanding of the underlying mechanisms, and the identification of new biomarkers to better appreciate related health benefits.

Inclusion Criteria:

• Postmenopausal women (absence of menstruation for at least 1 year and FSH > 40 IU/L)
• BMI between 27.0 and 39.9 kg/m²
• Sedentary or moderately active

Exclusion Criteria:

• Body weight change greater than 5 kg in the 3 months preceding the study
• Currently dieting or following specific dietary patterns
• Previous or planned bariatric surgery
• Food allergies or intolerances (particularly dairy proteins and lactose)
• Serious or problematic health conditions (e.g., renal insufficiency, diabetes, Cushing's disease, Paget's disease, parathyroid disorders, inflammatory bowel disease, uncontrolled thyroid disease, etc.)
• Fracture within the past year
• Hormone therapy
• Medications affecting bone metabolism (e.g., osteoporosis treatments, anti-estrogen therapy for breast cancer, epilepsy treatments)
• Antibiotic use within the 6 months preceding the study
• Use of probiotic supplements (capsules)
• More than two alcoholic drinks per day
• Smoking
• Drug abuse