The 'Heart Attack' hitmaker, who has battled bulimia in the past, took to Twitter last night (14.03.14) to vent her frustration after the 27-year-old singer performed 'Swine' at the South by Southwest festival in Texas, which involved vomiting artist Millie Brown.
Demi tweeted: ''Sad... As if we didn't have enough people glamorizing eat disorders already. Bottom line, it's not ''cool'' or ''artsy'' at all.
''Would you let someone bring a needle and shoot up on you? Addiction is addiction. (sic)''.
However, the 21-year-old singer was forced to defend herself after her honest comments didn't go down well with her fans.
She retaliated: ''It's not ''shade'' and it's not ''hate''. But someone has to come forward and say it and I'll take the heat for it. (sic)''.
Demi then reached out to Lady Gaga directly, writing: ''@ladygaga you're SO talented, if not one of the most talented in our industry PERIOD. Dope is INCREDIBLE.. but you don't have to do that (sic)''.
Meanwhile, Lady Gaga - who has also struggled with body image in the past - said yesterday she fears she had got ''really fat'' during her stay in Austin, Texas.
Millie, who has worked with Lady Gaga before, performs her stunt by drinking coloured milk before sticking her fingers down her throat and vomiting the liquid back up.
Many ticket-holders couldn't get into the O2 Arena show on Tuesday night (September 19th) because they didn't bring photo ID to match their booking.
An album re-release, a new song and a documentary mark the singer's legacy this year.
The actor plays the titular hero in the forthcoming adaptation.