How intestinal bacteria can elicit physiological functions from food components is becoming clear. The metabolism of intestinal bacteria induces molecules from food components that cannot be produced by the host, and these molecules create new physiological functions that have not been discovered before, as found in the intestinal bacterial metabolites of polyunsaturated fatty acids described in this chapter. By analyzing the newly discovered food-derived unsaturated fatty acid saturation metabolism in Lactobacillus plantarum AKU1009, an intestinal bacterium, hydroxy fatty acids (hydrated), oxo/enone fatty acids, partially saturated fatty acids, and conjugated fatty acids were found as novel metabolic intermediates that cannot be produced by the host and confirmed the existence of these fatty acids in the host tissues. The novel fatty acid metabolites showed unique physiological activities supporting our health. For example, ω6 fatty acid metabolites exhibit ω3 fatty acid-like activity. Expansion of the function of ω3 fatty acids was observed with intestinal bacterial metabolites of ω3 fatty acids. These metabolites, produced from the food components by the intestinal bacteria, were applied to functional food and pharmaceutical materials as postbiotics. As an example, 10-hydroxy-cis-12-octadecenoic acid (HYA), a hydroxy (hydrated) fatty acid that is an early metabolite of linoleic acid and showed various health-promoting activities such as anti-obesity activity, anti-diabetic activity, and anti-inflammatory activity, was developed as a material for supplement foods.