“I've struggled with an eating disorder since I was a child,” writes the actor, 26, in a column.
“This struggle has been mostly a private one, a war nobody knew was raging inside me. I tried to fight it alone for a long time. And I nearly died.”
The Girls actor says her problem with food started when she was a young child.
"I was told I was fat for the first time when I was eight. I'm not fat; I've never been fat,” writes Mamet in the September issue of Glamour Magazine.
“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.”
It led to years of Mamet abusing her body, starving herself and exercising too much in order to achieve an impossible ideal.
“I was only 17, living in misery, waiting to die,” she writes.
She says it took an intervention from her family to make her realise she had a very real problem.
“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,’” Mamet recalls.
“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."
Unfortunately the American actor says her treatment didn’t do much to help the actual problem, which was more about control than body weight or food.
“Everything I ate was written down. And I did eat; I looked cured on the outside. But the monster inside wasn't brought to trial,” Mamet says.
“So I was given permission to leave the hospital and enter back into the world as a "healthy" person. Then I went away for the summer and lost every pound I'd gained. Nobody had helped me dissect why I'd abused myself.”
Mamet says she’s an addict in recovery, but it’s a problem she will always have to work to manage.
“I'm at a healthy weight, though I realize that my obsession will always be with me in some way. For years the voice inside me has gotten louder or quieter at times,” writes Mamet.
She says society and the media are to blame for the prevalence of eating disorders.
“Our culture delivers a real one-two punch: You want to control something, and then society says, ‘Hey, how about controlling the way you look? Skinny is beautiful,’ ” Mamet writes.
“Your obsession feels justified. It's no secret that we live in a country with a warped view of beauty. ‘Skinny’ sells us everything, from vacations to underwear, effectively.”
The actor points out that skinny is not a standard body type, and says we need to talk about eating disorders as a problem to end the stigma of trying to be a perfect size.
“The first step, I think, is for those of us who are suffering to start talking about it: people like me, who have been diagnosed, and people who live in that grey area of ‘food control issues,’ ” says Mamet.
“We all suffer in some small way; we are all a little bit ashamed of that second cupcake.”
“Let's remind one another that we're beautiful. Maybe you'll help a friend. Maybe you'll help yourself.
“And if you're reading this and you're suffering, please know you're not alone. Tell someone: The people who love you will listen, I promise. And you'll feel better.”
I will say, as a longtime sufferer of an eating disorder I find it refreshing when people find it in themselves to share their story and struggle.