She previously weighed 50kg and said she had "horrible" skin, dark mood swings and brittle hair as a result of exercising too much and not eating enough.
The 2020 photo shows Simpson grinning from ear to ear, wearing a red string bikini that shows off the body she's sculpted with hard work over five years.
She also showed off her booty transformation following her weight gain, telling her 1.9 million followers there was "no quick fix".
"No photoshop. No short cuts. No quick fixes. No skinny teas. No waist trainers. Just 4+ years of consistency, hard work & dedication," she said.
"My journey is far from over – I see myself as a work in progress. I've learned that the beauty isn't in reaching your end goal, but it lies within finding your true self & being proud of your successes along the way."