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Rob Gronkowski's post-NFL routine includes 24-hour fasts, Tom Brady-type workouts and Sudoku

Rob Gronkowski in a publicity shot for his Fitplan partnership released in January.
Credit: Fitplan

Former New England Patriots tight end Rob Gronkowski — aka "Gronk" — won three Super Bowls during his nine years in the NFL and has earned more than $50 million. But Gronkowski says since retiring in March, he feels better than ever.

"I feel like I've definitely transformed ever since I stopped playing football. I feel like I transformed in a better way," Gronkowski tells CNBC Make It.

Gronkowski says he lost about 10 to 15 pounds by changing his diet "tremendously," doing stability workouts that he learned from his former Patriots teammate Tom Brady, and by calming his mind doing Sudoku puzzles.

"I just got the [Sudoku] book and there's like 150 physical puzzles in it, and I knocked out 15 already this week," Gronkowski says. "It gets you thinking, it gets your mind thinking and gets you going. It gets the wheels turning."

Since hanging up his Patriots jersey, Gronkowski, 30 has also been experimenting with intermittent fasting, which typically entails eating during a set window of six to eight hours and fasting for the remaining 16 to 18 hours. Intermittent fasting has become trendy among Silicon Valley tycoons like Twitter's Jack Dorsey and celebrities like Jennifer Aniston, but Gronkowski says he was turned on to the idea by a couple of friends and one of his brothers who tried it.

"[I fast] every other day, you know, depending on what I'm doing, where I'm traveling," Gronkowski says, adding that he never does a long fast on days he has a tough workout. But he does dabble with doing longer fasts. "I just did my longest fast this week, about six days ago, it was for 24 hours," Gronkowski tells CNBC Make It on Tuesday.

Gronkowski says he felt great afterward, less bloated. And while there is some research that shows intermittent fasting can lead to weight loss, there hasn't been enough research on humans to support cognitive benefits or whether fasting is healthy or sustainable long term. And fasts lasting longer than 12 hours can be dangerous, especially for individuals who have specific health conditions or take certain medications, according to the National Institutes of Health.

In addition to intermittent fasting, Gronkowski says post NFL he's gone from eating whatever he wanted (think lots of burgers and fries) to organic fruits and vegetables.

"Growing up in Buffalo, I would eat anything. I'm talking like anything. Chicken wings with as much ranch and blue cheese dressing as you can," he says.

Rob Gronkowski in 2015 answering questions during Super Bowl XLIX Media Day at US Airways Center in Phoenix, Arizona. Gronkowski says he weighed about 260 when he played and is around 250 today.
(Photo by Chris Coduto/Icon Sportswire/Corbis/Icon Sportswire via Getty Images)

Now Gronkowski says he sticks with plant-based protein shakes with almond butter, chia seeds and fruit for recovery after workouts and has chicken with veggies like green beans, broccoli or asparagus with quinoa or sweet potatoes for lunch and dinner. (It's similar to his pal Tom Brady's diet.)

"At one point I was [down to] 240, which was about a 20-pound loss. But I'm 250 now and I played at about 260," says Gronkowski, who is 6-foot-6.

He says he made the change because as he's gotten older, "I wanted to lose. I had bloated weight."

Gronkowski also sticks with a tough workout regimen six to seven days a week because he believes exercise is the key to maintaining peak performance.

In January, Gronkowski partnered with Fitplan to become a personal trainer on the app so users can get his exact routine.

"People always ask me what I do," he says. "I wanted to give people what I've learned throughout the years, and I truly believe that the best workouts start with stability," which focuses on the core.

Since before he left the NFL, Gronkowski has been following a version of Tom Brady's TB12 method (designed by Brady's longtime trainer Alex Guerrero), with a "Gronk twist," he says. The workout focuses on speed, agility and core stability, using resistance bands instead of weights. Heavy weights create short, tear prone muscle fibers built for quick bursts, according to Guerrero.

In addition to puzzles, eating healthy and working out, Gronkowski says he tries to meditate whenever he can. While he admits he' s not consistent, he believes in the practice

As for work, since October, Gronkowski has been serving as an analyst for FOX NFL Sunday.

"It feels good just to go out there and try to find things that I just love to do," he says about his new chapter.

Clearly Tom Brady has been a big influence on Gronkowski's post-NFL health and fitness plan. So what does he think Brady's next move will be now that he's a free agent? Gronkowski doesn't know, but he's sure his friend is "checking out all his options."

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Inside former Patriot Rob Gronkowski's $2.3 million Boston condo
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