Lindsay Lohan. (AP File)

Actress Lindsay Lohan has lashed out at rumours she's embarked on a liquid diet to maintain her slim physique, insisting people need to "mind their own business".

The Mean Girls star, 22, has been the subject of much tabloid speculation in recent months after showing off her skinny frame in a variety of flesh-baring outfits.

The latest reports suggested Lohan is currently surviving on a diet of energy drink Red Bull - but the star has slammed the claims.

Her representative tells People.com, "Lindsay has always enjoyed a Red Bull, but she eats. Everybody needs to mind their own business and stop worrying about what Lindsay eats or doesn't eat."

Lohan's denial comes just weeks after her mother Dina urged her to eat more hamburgers following concerns for her health.

Dina told U.S. news show Access Hollywood, "I'm a mum. If I see my daughter a little thin, I say, 'Eat more McDonald's.' I told Lindsay I think she’s a little thin."