"I was told I was fat for the first time when I was eight. I'm not fat; I've never been fat. But ever since then, there has been a monster in my brain that tells me I am - that convinces me my clothes don't fit or that I've eaten too much.
"At times it has forced me to starve myself, to run extra miles, to abuse my body."
The actress, now 26, credits her famous father for forcing her to get help during her late teens, an intervention which saved her life.
"My dad eventually got me into treatment. He came home one night from a party, took me by the shoulders, and said, 'You're not allowed to die.' It was the first time I realised this wasn't all about me. I didn't care if I died, but my family did. That's the thing about these kinds of disorders: They're consuming; they make you egocentric; they're all you can see.
"During treatment I discovered that my disorder has never really been about weight or food - that's just the way the monster manifests itself. Really these diseases are about control: control of your life and of your body."
Her Girls co-star, and the creator of the show Lena Dunham, heaped praise on Mamet for the honest piece.
Proud of my colleague @ZosiaRMamet, beautiful in body and soul, for opening up about her eating disorder struggle. http://t.co/nMynE73Wej
Mamet is the latest celebrity to share her eating disorder story - singers Demi Lovato and Kesha have been open about their body issues in recent months, after each enduring stints in rehab, in a bid to help others struggling with similar problems.
* Read Mamet's full column here.
- WENN