The singer made the admission during her second 'California Dreams' show at London's O2 arena on Saturday.
After performing her Teenage Dream track 'Not Like The Movies', Perry told the 15,000-strong audience: "My favourite place in the world might just be London."
While rubbing her stomach, she added: "I didn't know if I was going to be able to show up tonight.
"I'm not rubbing my belly because I'm pregnant, I'm rubbing because I ate beans on toast. You were going to need a crane to lift my arse in here."
The star continued to praise the UK, saying that the country has her "favourite food, shops and musicians [from] Adele to Morrissey".
Perry played a packed show for the 95th gig of her 'California Dreams' world tour.
She started the set with 'Teenage Dream' and played all of her popular hits, concluding with 'California Gurls for the encore.
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Katy Perry's setlist was as follows:
'Waking Up In Vegas'
'Ur So Gay'
'I Kissed A Girl'
'Circle the Drain'
'Who Am I Living For?'
'Not Like The Movies'
'The One That Got Away'
'Thinking Of You'
'Hot N Cold'
'Last Friday Night (T.G.I.F.)'
'I Wanna Dance With Somebody' (Whitney Houston cover)
Listen to Katy Perry's new single 'The One That Got Away' below: