Naturally occurring lecithins and/or oleic acid stimulate the growth and lactic acid producing activity of Lactobacillus and Bifidobacterium species of probiotic bacteria, and replace polysorbate 80 for those products. They can be used in naturally occurring form, or where they are to be combined with probiotics in a carrier, or they can be treated to yield a stable powdered form of these naturally oily compounds. They can be sold as combined prebiotic/probiotic formulations in the same carrier, or sold as separate dietary supplements, e.g., in capsule or tablet form, to be used with the probiotic formulation as desired.