"There's always a lot of that around at this time of year so here's a little something to shake up your feed," the body-positive activist wrote.
"Today I went to the beach in possibly the most revealing bikini I've worn in a very long while, and I had a great time."
"The top basically has my cleavage on full show thanks to the lace-up detailing (HELLO) and the bottoms … are way lower than I'd usually wear."
Ms Kerr said while she normally chose swimwear with a high rise to cover her "lopsided and saggy stomach", she decided to shun these as a way to fight against social pressures.
"I really wanted to feel the sun on my belly and the sea on my skin, so I put on a pair that has been sitting in a drawer for about two years with the tags still on," she said.
"They don't even cover my belly button, and you know what? I don't care.
"I sat on the sand and had a picnic, I swam with my family, I soaked up the sunshine and had a great time.
"Looking forward to much more of this over summer."
The "real" photos struck a chord with Ms Kerr's followers, with the post garnering more than 1400 reactions and a raft of positive messages.
"I love this post! And I love how pics like this help wahine (women) like me deconstruct our thinking. You look rad," one wrote.
"Love this!! You are rocking that bikini," another said.
"These are flippin' phenomenal swimmers and you are GLORIOUS," one added.
Another said: "Thank you for being one less bloody diet ad on my feed, seriously it's ridiculous how many there are this week."
Others agreed, saying they were also astounded by the amount of diet advertising they had been hit with over the past few days.
"I don't know whether I am feeling more down about myself, but I feel like the 'diet your way into a better you in the new year' schtick has been even louder and more invasive this time around!" they said.
In a recent interview with Stuff, Ms Kerr said she had no problem at all with people who decided to take up health programs at this time of year.
"I'm not against people joining a gym, I think gyms are great, but the advertising is geared towards weight loss and preying on the fact that people are feeling insecure about their bodies because it's summer," she told the publication.
"It's just the way that they advertise. They're not focused on health, they're not focused on strength, they're not focused on fitness, it's literally preying on body insecurities."
In a follow-up Instagram post, Ms Kerr reiterated her message that dieting wasn't a guaranteed pathway to happiness, self-confidence or self-love.
"You do not have to change your body to earn your place in the world," she said.
"You are enough just as you are. I used to think that I had to shrink myself to fit in, that I wasn't worth anything if I didn't look a certain way.
"And that's a huge mind f**k, especially if you look very different to the ideal like I do (hello, short fat Maori woman over here)."
She said by speaking openly she wanted people to know that no matter "what size a person was, how old they were, what they looked like or their background, "it's okay".
"You are worth love and respect (from yourself and others) and good things NOW. Just as you are," she said.
Ms Kerr ended her post by telling her followers while it can be difficult to discard "negative messaging" ingrained from childhood, she hoped to offer an inspiring "reminder".
"I wanted to tell you anyway because sometimes we just need a reminder," she said.
