The 22-year-old - who is currently loved-up with musician Thomas Cohen - is thought to have slimmed down from 10st to 8½st in just four months.
'Peaches says it really is true love this time, so she's decided to turn her life around,' a source told Now magazine.
'She wants to avoid being in the papers for the wrong reasons, so she's stopped the wild partying and has been working-out like crazy, and eating healthily.'
Meanwhile the 5ft 7in model defended her weight loss, insisting she's still eating properly.
'To those telling me I look skinny and to eat something, I can assure you I've just cut out eating crap,” she wrote on her Twitter page.
'I still eat like a horse, guys!'