This multicentric, randomized, double-blind and controlled study aims to examine the effect of a fermented dairy product containing the probiotic Lactobacillus casei DN-114 001 (Actimel® = tested product) on the incidence of respiratory and gastro-intestinal common infectious diseases (cumulated number of infections during the intervention period: primary criteria), and on the Quality of Life in adults submitted to multi-stressor situation. Volunteers received either 200g/day of tested product (N=121) or control product (N=118) for 7-weeks.

Inclusion Criteria:

• male and female aged 18-29 years
• attending 7 weeks of firemen training school
• a 19 to 29 kg/m2 body mass index
• found medically healthy (in particular, free of respiratory and GI tract symptoms)
• agreeing to a written informed consent, and who appreciates dairy products and multi-fruit flavour.

Exclusion Criteria:

• Subject who is not reading and writing French, or not understanding informed consent or study protocol
• subject with allergy or hypersensitivity to milk proteins or dairy foods components (ex: lactose), or with any known food or respiratory allergy;
• subject presenting a severe evolutive or chronic pathology (Ex: cancer, tuberculosis, Crohn disease, cirrhosis, multiple sclerosis, Type I diabetes…) or any past or actual health condition that may interfere with the outcome of the study (Ex: HIV, Chemotherapy, malabsorption, ulcer, celiac disease…)
• subject having experienced any infectious disease during the last 7 days
• subject with current diarrhoea or constipation
• subject who is frequently using laxatives or who has been using laxatives during the week prior his participation to the study
• subject who was under artificial nutrition, had gastro-intestinal surgery or any intervention requiring general anaesthesia the last 2 months prior to his participation to the study
• subject with special medicated diet (obesity, anorexia, metabolic pathology, nutritional complementation…) or with eating disorders (anorexia, bulimia, alcoholism…)
• subject currently receiving, or who has received during the last months, systemic treatment or topical treatment likely to interfere with evaluation of the study parameters: antibiotics, antiseptics,antifungal, corticoids, vaccines, anti-histaminic molecules, non-corticoid anti-inflammatory substances, immunosuppressant treatment…
• subject already enrolled in another clinical study, or currently under an exemption period from a previous study
• female subject who is currently pregnant or breast-feeding, or willing to become pregnant during the 2 coming months after enrolment in the study
• subject in a situation which in the investigator's opinion could interfere with optimal participation in the present study or could constitute a special risk for the subject