"Started right here with these milkshakes hahaha," he wrote, next to a throwback Thursday photo of his enjoying desert.
Kardashian, 28, has been open on social media about his effort to get back in shape.
Earlier this week, he wrote, "Spotted these fools on the morning workout," next to a picture of his sister Kylie.
This isn't the first time the reality star has posted a throwback pic eating food.
"Me just chill-zoning in Malibu eating a pulled pork sandwich," he posted a month back.
Kardashian's trainer Gunnar Peterson told People magazine earlier in the week that he's been hitting the gym hard. Good to see he's mixing humor in with the hard work.