According to Wikipedia, Mulligan Stew was
. . .an American children’s educational television series, produced and sponsored by the USDA Extension Service and its youth outreach program, 4-H. . . . The six-episode series follows the adventures of a group of five school-age musicians and their mentor, all dedicated to teaching others about good nutrition and developing healthier eating habits. “
Episode 3, “The Film Flam Man,” follows the children as they encounter someone selling a fad diet.
The Stews shun Mulligan when he refuses to follow the direction of a macrobiotics-like fad diet promoter, who tricks the rest of the kids into trying his fad diets. A concerned Mulligan frantically seeks assistance from Wilbur, who engages the con man in a nutritional duel. Mulligan is ultimately proven correct, but not without some anguish on everyone’s part.
The US National Archives YouTube channel recently uploaded the full episode in all its glory.