A functional food is a compound that, being or not a nutrient, has a positive effect on one or several functions in the organism, producing well-being in the animal. The following compounds are considered functional foods: prebiotics, probiotics, symbiotics, antioxidants, secondary products of plant metabolism, structural lipids, polyunsaturated fatty acids, fat metabolism byproducts, bioactive peptides, fi ber, vitamins and minerals. Prebiotics, probiotics and symbiotics are modifi ers of the intestinal microfl ora increasing mainly lactobacilli and bifi dobacteria populations and reducing pathogenic bacteria. Lactobacilli and bifi - dobacteria use oligosaccharides and fructo-oligosaccharides arriving at the colon, producing fatty acids and freeing minerals to be absorbed and utilized by the host. Prebiotics are partially-digestible oligosaccharides; probiotics are microorganisms (mainly lactobacilli and bifi dobacteria); and symbiotics are a mixture of probiotics and prebiotics. During the weaning period, piglets face dramatic changes in feeding management and environment, affecting feed intake and, at the same time, affecting digestive functions resulting in lower growth and higher incidence of disease, mainly diarrhea. Functional food may be an alternative to reduce the effects of weaning on growth performance and health of piglets, to diminish or to avoid gastrointestinal problems during weaning, preventing the proliferation of pathogenic bacteria, and improving digestive functions. All these may help to withdraw antibiotics from piglet feed.