What IS the keto diet, anyway? 

Former quarterback and current baseball athlete Tim Tebow — who's been eating keto since 2012 — puts it simply. 

"What keto really is — to sum it up — is high fat, moderate protein, low to no carbs and sugar," he says. And by high fat, he means the good kind — like those found in avocados and olive oil.

RELATED: List of Foods To Eat & Avoid On Keto Diet, According To Dr. Ian Smith

So, how did Tim get into keto dieting in the first place?  

"When I was playing [football]," he tells Rach, "I was always looking for that next [diet], the best thing. I tried a lot of different diets, and then in 2012 — really before most people knew about keto — I started it." 

"A trainer I worked with told me about it," he continues, "and he told me what was happening for so many people. I tried it, I loved it." And he's not the only person in his family to start following the trendy diet.

When his father was diagnosed with Parkinson's disease, his doctor advised him to try keto. "When you have Parkinson's, [the brain] slows down a little bit," Tim explains. "[They believed] all of the good fats would help his brain." 

"It kind of changed our whole family and the way we ate," the former quarterback says.

Now, to set the record straight, he's not claiming that the keto diet is right for everybody (he says even his fiancée can't fully commit to it).

For starters, while actress Vanessa Hudgens once told us she lost 10 pounds on a low-carb, high-fat diet, celebrity trainer Jillian Michaels has famously spoken out against the keto diet.

But "what a lot of people can agree on is that sugar and carbs are the enemy," Time tells Rach. 

Because she knew Tim was visiting, Rach made Keto Lasagna-Style Stuffed Zucchini just for him. (And for the record, we think keto believers and critics can also agree that it's delicious, no matter what diet you follow.)

As always, talk to your doctor before making significant dietary changes.