Perez is off to a torrid start. In two spring games, he is 4-for-5 with two homers, two doubles and eight RBIs.
"He's as light as he's been in five or six years," Yost said. "He looks fantastic."
Yost isn't surprised that Perez put in the offseason work.
"He did it on his own," Yost said. "We didn't call him up and say 'Lose weight.' We didn't because he's always been productive. His weight never interfered with his game plan. But the lighter you are, it takes the workload off you a little bit. It's easier working with 25 pounds less than 25 pound more. It's to his benefit.
"And Salvy has always been a guy who wants to work hard to be in a position to be the best he can possibly be."
So far, Yost hasn't noticed a significant change in Perez defensively.
"Nah, he doesn't look that different on the field," Yost said. "He's always, for me, been very athletic for a big guy. But [losing weight] will take pressure off his legs.
"And [coach] Pedro [Grifol] always tells the catchers to stay quick and stay light. Sal was always a guy who lost weight during the season. But his focus this year was to lose the weight first and then maintain it."
Perez is determined not to put the weight back on.
"I hopefully can stay like this the rest of my career," Perez said.
Jeffrey Flanagan has covered the Royals since 1991, and for MLB.com since 2015. Follow him on Twitter @FlannyMLB. This story was not subject to the approval of Major League Baseball or its clubs.