This is an exploratory cluster randomized controlled trial to evaluate the effect of a kefir beverage, enriched with prebiotics components, on immunity, lipid profile and adiposity in a population-based study, using the family as the intervention unit.

The gastrointestinal tract is populated by a collection of microorganisms, primarily bacteria, that interact with intestinal host cells. In the past two decades, several studies have demonstrated the effects of the intestinal microbiota on host physiological, metabolic and immunological processes and have revealed that the microbiota is fundamental to host body function. There is currently a growing interest in manipulating the intestinal microbiota to enhance the effects on health and welfare of the intestine. In this regard, since its introduction, the concept of prebiotics has stimulated both scientific and industrial interest. A dietary prebiotic is a selectively fermented ingredient that results in specific changes, in the composition and/or activity of the gastrointestinal microbiota, thus conferring benefits upon host health. To date, the prebiotics most widely evaluated in human clinical trials are inulin-type fructans (inulin, fructo-oligosaccharides, oligofructose) and galacto-oligosaccharides (GOS).

The investigators goal is to conduct a human clinical trial to evaluate the impacts of a functional-prebiotic beverage on immunity and metabolic profile.

This study will be performed on a family-oriented basis. 44 families/clusters (~ 150 children and adults, older than 3 years) will be selected to participate in the study and will be randomized into intervention group (n=22 families) and control (n=22 families) groups.

Weight, body mass index (BMI), waist circumference (WC), nutrient intake from food frequency questionnaire, physical activity, blood pressure, allergic sensitization, metabolic function (fasting blood glucose, HbA1c, insulin resistance and lipid profile), general lymphocyte overview (B-cells, T-cells and NK-cells) and sub-populations of T-helper cells (Th1, Th2, Th17 and T-regulatory), inflammation markers (C-reactive protein, interleukin-6 and tumor necrosis factor-alpha) will be measured at baseline and after 4 months.

Mixed effect models analysis will be performed to assess changes in the cardiometabolic and immune parameters.

Inclusion Criteria:

1. For the index subject:

   • Female or male.
   • 18 years and older.
   • Living in a family unit with two or more people.

2. For the other family members:

   • Female or male.
   • Age between 3 to 85 years.

3. At family level: at least two members will meet inclusion criteria but no exclusion criterion

Exclusion Criteria for the index subject and the other family members:

• Alcoholism
• Pregnant
• Major cardiovascular disease
• Dementia
• Major autoimmune diseases
• Diseases or treatments that seriously affect the immune status
• Neoplasia
• Terminal disease

Both groups will receive fermented dairy products with similar color, flavor and nutritional composition, except the prebiotic components, which will only be administered to the intervention group.