Letterman asked the legendary comic -- who turns 80 on June 8 -- about her experience at Sunday's Academy Awards, which she described as "a lot of new faces on a lot of old bodies."
"What is her song? Rolling in the deep?" Joan asked. "She should add fried chicken!"
Joan then joked she overheard Adele complaining, "My throat, my throat, I don't know if I can swallow!"
"I said, 'Oh, yeah -- you can swallow!'" Joan quipped.
Watch the video on RadarOnline.com
It's not the first time Joan has razzed the singer about her weight: After Adele gave birth last fall, Joan tweeted, "Congratulations to Adele on the birth of her 68 pound 8 ounces bouncing baby boy."