Credit: Instagram

16 and Pregnant's Mackenzie Douthit, has a pretty rockin' body, especially considering that she swelled up to the size of an enormous watermelon before giving birth to Gannon.

So, how does the rumored Teen Mom 3 cast member stay so fit? She says it's all about what you eat and drink — and how you take care of your body.

The good news? According to Mackenzie's health plan, there's no need to diet!

"i dont diet," Mackenzie tweeted a curious fan. "but i dont eat after supper,drink lots of water and ONLY water.but it is VERY important that you work out everyday."

Sounds pretty simple, right gang? Just lots of water and plenty of exercise! Although we don't know if we can give up our midnight snacks. Girls gotta eat.

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