The writer, activist and Girls creator said that in the left picture, where she is visibly slimmer, she was "sick in the head and tissues", whereas now she's "happy, joyous, and free."
"On the left: 138 pounds, complimented all day and propositioned by men and on the cover of a tabloid about diets that work. Also, sick in the tissue and in the head and subsisting only on small amounts of sugar, tons of caffeine and a purse pharmacy," she wrote.
"On the right: 162 pounds, happy joyous & free, complimented only by people that matter for reasons that matter, subsisting on a steady flow of fun/healthy snacks and apps and entrees, strong from lifting dogs and spirits."
"Even this OG body positivity warrior sometimes looks at the left picture longingly, until I remember the impossible pain that brought me there and onto my proverbial knees. As I type I can feel my back fat rolling up under my shoulder blades. I lean in."
In just seven hours, the post has racked up over 373k likes, far more than Dunham's usual count (around 18k per photo). "Wow. This is profound and so beautiful," one fan commented. "Lena, you are an example for all women that suffer every day with this beauty dictatorship. I'm feeling represented on this post. Thank you!" another wrote.
Of course, this isn't the first time the 32-year-old has spoken out about body image. Last year, she shared a magazine cover which had a photo of her beside the words, "20 slimdown diet tips," writing that "anxiety disorder" and "resultant constant nausea" are two of her real "diet tips."