"I am genuinely honoured to be on your cover and so happy you licensed a pic by @ruvenafanador, who always makes me feel gorgeous," she wrote. "BUT this is NOT what my body has ever looked like or will ever look like - the magazine has done more than the average photoshop. So if you're into what I do, why not be honest with your readers? Much love, Lena."
The post quickly attracted comments from fans praising Lena for her words, as well as over 37,000 'likes'.
Lena has previously spoken about where she gets her body confidence from, insisting it is down to her parents, Carroll Dunham and Laurie Simmons.
"My parents both have really healthy attitudes about their own bodies but also about the range of things that can be beautiful," she told Marie Claire magazine. "But they also just always made me feel pretty and cool and smart, even in the moments when I have known - and still know - that my body wasn't fitting into a traditional Hollywood idea of the female body.
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"This could very easily be taken out of context, and I think it's funny now, but I remember looking in the mirror as a kid and it would be like for an hour at a time, and I'd be like, 'I'm just so beautiful. Everybody is so lucky that they get to look at me.' And of course that changes as you get older, but I may have held on to that little-kid feeling that was me alone in my bathroom."
- WENN
