Omega-3 fatty acids are polyunsaturated fatty acids found in certain fish tissues, and in vegetable sources such as flax seeds, hemp seeds, walnuts, and canola oil — though some sources contain other substances which may counteract the beneficial Omega-3 (see sections Omega-3 - Omega-6 balance, and Dietary sources below). Such fatty acids are also more prevalent in grass-fed or pasture-finished livestock, compared to those fed a diet high in grains.