Wallace and conservative radio host Mike Gallagher got into a discussion about fat-shaming on Gallagher's radio show on Friday.
"Have you seen Kelly Clarkson?" Gallagher asked. "Holy cow, did she blow up."
Initially, Wallace tried to evade the comment, noting American Idol winner Clarkson has "a lovely voice." But later, he came back to it, saying, "She could stay off the deep-dish pizza for a little while."
Wallace's Fox News colleague Greta Van Susteren wrote on her blog that Wallace should apologize for his remarks.