Thin, thedirectorial debut from photographer Lauren Greenfield, has won this year's Grierson Award for the best feature-length documentaryscreened at The Times BFI London Film Festival.

The documentary follows fourwomen as they struggle to overcome eating disorders in a US clinic. SandraHebron, artistic director of the festival, described it as a "powerful andimportant film, allowing us to witness at close hand the complexities of thispersistent and damaging illness".

The award, made by the Grierson Trust, which commemorates Scottish documentary film-makerJohn Grierson, will be presented on Thursday 26October at London's National Film Theatre.