According to the box, whoever eats the supplements gets increased muscle-strength, performance abilities as well as a much larger, more muscular and hairier appearance. It also deepens a person's voice and makes it sound more masculine (especially in Anais's case).
The protein supplements first appeared at the beginning of "The Mustache" when the mailman brings in the mail for the Watterson family. When Richard runs off crying, he mistakenly takes the kids' breakfast cereal, leaving behind his box of protein supplements, which the kids unknowingly eat, thinking it is their cereal. During school that same day, Gumball and Darwin go through various physical changes and somehow become "men."
When they leave school, realizing that they do not have to listen to Miss Simian now that they are adults, they initially enjoy adult life, but quickly realize that being adults is not as good as they thought it would be. While in a run down, a large looming figure comes in. The boys initially think it is their landlord, but the figure turns out to be their sister, who Gumball says "looks like a Mexican wrestler." Anais explains to her brothers that the whole thing was just a big misunderstanding and urges them to come with her so she can explain it.
After the kids finally get home (freaking their parents out with their new appearances) and Nicole questions what happened to them, Anais shows Nicole the box of protein supplements. When Richard admits that he ordered the box of supplements and Nicole asks someone to explain what is going on, Anais does so: as Anais deduces, Richard must have taken the breakfast cereal by mistake, leaving behind his protein supplements, which the kids unknowingly ate in lieu of their regular cereal.
When Nicole questions Richard on why he bought the supplements in the first place, Richard admits that whenever he checks his e-mails, the advertisements intimidate him into buying whatever they are selling. After Nicole and the kids assure Richard they love him no matter what (followed by the kids nearly crushing their parents in a group hug with their newfound strength), Gumball worries that he and his siblings will stay the way they are now forever.
When Nicole checks the box of protein supplements, however, she discovers that the effects are only temporary and are supposed to wear off after at least one week.
- While the protein supplements are obviously geared towards men, the supplements affect women too.
- Oddly enough, Richard's supplements affected Anais the most, despite her being a female child. This mirrors the effects of testosterone supplements on females, where they develop male-like characteristics.