CLAIM: Having Tonsil Surgery Leads To Weight Gain. “No one knows how to explain it, but studies show a link between the surgery and weight gain. . . . But so far only an association has been confirmed, not a direct causal effect. For now, experts say parents should simply keep an eye on a child’s weight after the surgery.” Hmm. On the other hand, tonsillectomies used to be routine, and kids used to be a lot skinnier.