The co-evolution of man and microbiota has diversified the nutrients compatible with human digestion and thus survival. The increased fitness obtained from a better access to food has favored the development of mechanisms able to protect and preserve microbiota diversity, such as barrier function and host immunity. Man consumes more than 50000L of liquid and 30 tons of food in a lifetime. Nutrients therefore constitute a major environmental exposure to man, which can both protect from as well as lead to malnutrition, obesity, allergy etc. It is likely that the impact of nutrients on physiopathology are mediated by alterations in barrier function and host immunity. Here we propose to evaluate the effects of pre- and probiotics administered to pregnant women and their child in early-life. The effect will be assessed clinically (food allergy) and associated with measures of barrier function and host immunity. The consortium of 5 partners will evaluate clinical outcome, humoral and cellular host immunity as well as microbiota ecology in feces and breastmilk. We expect to observe alterations of gut microbiota ecology associated with modifications of host immunity to commensal microbes caused by nutritional interventions with pre- and probiotics. We hope to be able to support the transition to healthy food alternatives, which could reduce risk of developing food allergy in early-life.