MSG remains controversal, but glutamate is found naturally in many natural sources—including fish sauce, mushrooms, tomatoes, and walnutsincluding fish sauce, mushrooms, tomatoes, and walnuts.Masan's product Nam Ngu fish sauce are displayed for sale at a market in Hanoi (Photo: Nguyen Huy Kham/Reuter).ish sauce is an indispensable ingredient in the cooking of Vietnam, Thailand, Burma, Cambodia, Laos, and the Philippines.