The singer, who supported a string of Adele's US shows earlier this year, revealed he has since lost the weight and is "the skinniest I've ever been".
Speaking at Jack Daniel's birthday gig in Tennessee, he said: "I spent six weeks on tour with Adele and I did a mini tour of the West Coast. I really enjoyed myself. I went up two suit sizes being there.
"I've come back and gone straight into training and lost two stone. I think this is the skinniest I've ever been."
Discussing his return to the States, he quipped: "I can feel all the great food and massive portions... I can see myself putting it back on. It's probably a good thing I'm going home again soon."
The 'She Said' star - whose real name is Ben Drew - performed a number of hits during his headline spot at the show; as well as renditions of Eddie Floyd's 'Big Bird' and 'Knock On Wood' and Isaac Hayes's 'Soul Man' backed by legendary producer Steve Cropper.
Drew added: "They're the three songs where I felt the least chance of embarrassing myself. I could have sang 'Sitting On The Dock Of A Bay', but I felt unless you can sing it as good as or better than the original... you'll make a fool of yourself."
Plan B recently told Digital Spy he felt "ready" to take on America.
> Plan B to form punk band with backing singers and stylist
Watch the singer's 'Prayin'' music video below: