The Grim Adventures of Billy and Mandy (2001)

S6E5 Major Cheese

Billy, Mandy, and Grim pay a visit to Mighty Moe, a senior who has unlocked the key to extending his life through a healthy lifestyle. Enthusiastic about sharing his findings, Moe plans to write a book detailing his wisdom. Concerned about the potential impact, Grim devises a plan to sabotage his efforts by tempting him with unhealthy snacks.