LOS ANGELES, May 26 (Reuters) - Film documentary "Super Size Me," a critical look at the health impact of a fast-food only diet, has been downsized at cable network MTV which has refused to air advertisements for the film, its distributors said on Wednesday. Roadside Attractions and Samuel Goldwyn Films said in a statement the cable TV channel targeted to young audiences has told them the ads are "disparaging to fast food restaurants." The distributors said MTV sister network VH1 was planning to use clips from the movie in a program called "Best Week Ever," but the clips were pulled...