DHA and EPA are concentrated in seafood, while ALA can be found in certain plant foods, like walnuts. Flax OilOmega-3s: 8.5 grams of ALA per tablespoonFlaxseed oil is the richest plant source of plant-based omega-3s you can eat. SardinesOmega-3s: 0.74 grams of DHA and 0.45 grams of EPA per 3-ounce servingSardines are an excellent source of omega-3s. TunaOmega-3s: 0.54 grams of DHA and 0.2 grams of EPA per 3-ounce servingTuna is a shelf-stable seafood option that’s high in omega-3s. Though walnuts provide ALA, there are plenty of other foods that are higher in ALA and that contain DHA and EPA.