Demi Lovato has hit out at Lady Gaga for "glamorizing" eating disorders in her controversial SWSX performance Thursday night.

The "Heart Attack" hitmaker, who has battled bulimia in the past, took to Twitter to vent her frustration after Lady Gaga performed "Swine" at the South by Southwest festival in Texas. The performance incorporated a scenario involving vomit artist Millie Brown.

Demi tweeted: "Sad... As if we didn't have enough people glamourizing 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."

After that tweet, Lovato was forced to defend herself -- when her 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."

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."

Meanwhile, Lady Gaga -- who has also struggled with body image in the past -- said she fears she had got "really fat" during her stay in Austin, Texas. "I have been eating BBQ all week," she told Jimmy Kimmel.

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.