Synbiotics refer to nutritional supplements combining probiotics and prebiotics in a form of synergism, hence synbiotics.
Probiotics are live bacteria which are intended to colonize the large intestine and confer physiological health benefits to the host. A prebiotic is a food or dietary supplement product that confers a health benefit on the host associated with modulating the microbiota. Prebiotics are not drugs, not functioning because of absorption of the component, not due to the component acting directly on the host, and are due to changes to the resident bacteria - either changing the proportions of the resident bacteria or the activities thereof. Measurable changes to the microbiota in the absence of a desirable physiological consequence in the host does not quality as a prebiotic. A prebiotic may be a fiber, but a fiber is not necessarily a prebiotic.
Using prebiotics and probiotics in combination is often described as synbiotic, but the United Nations Food & Agriculture Organization (FAO) recommends that the term “synbiotic” be used only if the net health benefit is synergistic. A further restriction is to require that the prebiotic be shown to increase the population and/or function of the probiotic it is paired with.
Examples
FAO Technical Meeting on Prebiotics. Food and Agricultural Organization of the United Nations. 2007.
de Vrese M, Schrezenmeir J. Probiotics, prebiotics, and synbiotics. Adv Biochem Eng Biotechnol. 2008;111:1-66.
Vandenplas Y, De Hert SG; et al. Randomized clinical trial: the synbiotic food supplement Probiotical vs. placebo for acute gastroenteritis in children. Aliment Pharmacol Ther 2011;34(8):862-867.
Björklund M, Ouwehand AC, et al. Gut microbiota of healthy elderly NSAID users is selectively modified with the administration of Lactobacillus acidophilus NCFM and lactitol. Age (Dordr) 2011 (in press).
Fateh R, Iravani S, et al. Synbiotic preparation in men suffering from functional constipation: a randomised controlled trial. Swiss Med Wkly. 2011 Jul 30;141:w13239.
Simakachorn N, Bibiloni R, et al. Tolerance, safety and effect on the faecal microbiota of an enteral formula supplemented with pre- and probiotics in critically ill children. J Pediatr Gastroenterol Nutr 2011;53(2):174-181.