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Josh Jackson was always one of the biggest, strongest, most talented athletes on the court. It was like that when he was a kid growing up in San Diego, when he was in high school in Michigan and even recently during his one-year stint at the University of Kansas.

Then this summer the Phoenix Suns drafted him fourth overall. It didn't take Jackson long to learn just how different and difficult his basketball life was about to become.

"The physicality of the NBA game is crazy," he tells Bleacher Report. "Like our [third] game of the season, I'm f--king guarding Blake Griffin. And I'm barely 200 pounds."

Going from guarding 190-pound teens to a 6'10", 251-pound physical force would be a moment of on-court realization for any player that he is, um, no longer in Kansas anymore. No longer being the most talented player on the floor is just one of the many stresses NBA rookies face as they enter the world of being a professional.

Imagine, for example, having to beg your mom to stop cooking all of your favorite treats.

Upon discovering he'd have to get bigger and stronger to survive against veterans like Griffin, Jackson recently decided to alter his diet. That meant giving up all the fried food he devoured as a kid, a task that at times proved particularly confounding.

After all, his favorite chef was always in his midst.

"I had my mom in town for like two weeks, and she was just cooking everything," Jackson says. "I was like, 'Ma, I can't eat this!' That was one of the hardest parts."

Many of last year's rookies likewise dealt with the need to change their diet, and the difficulties that come with doing so. Five of the sophomores who spoke with Bleacher Report mentioned how prevalent fast food was in their lives while they were in college.

"Because you have no money in college, that's really all you can eat," Nets guard Caris LeVert says.

"At Marquette, we only had a couple of eating options: a Jimmy John's, a Subway, a Burger King—and most of it was in the dining hall," Pistons forward Henry Ellenson adds. "A major adjustment for me in the NBA was having to make dinner and find meals. And I can't really cook."

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His brother, Wayne, is a huge Food Network fan, so Henry enlisted his help. He also discovered life in the NBA comes with some dietary perks.

"Lobster rolls became my new favorite food," Ellenson says. "I was telling my mom, 'We don't really have it back in Wisconsin'"—where Ellenson grew up—"but I started getting it anytime we went out as a team in Boston or one of those East Coast cities."

With the help of their respective teams' training staffs, most rookies quickly adjust to this new dining hall-less world. Many of them welcome the opportunity to sample new foods in new spots, given how difficult it can be to fill the empty hours they suddenly find on their hands.

"There's just so much free time," LeVert says. "In college, you've got study hall, classes, film—all that stuff. In the NBA, it's just practices, games and that's it."

"You can really get bored," adds Bucks guard Malcolm Brogdon, last season's Rookie of the Year, echoing a sentiment from Hornets rookie Malik Monk that went viral late last month.

That's where hobbies come in. For LeVert, that meant watching movies at home, shopping or strolling around Brooklyn. For Brogdon, the countless hours spent flying to and from games provided an opportunity to plow through books like Ta-Nehisi Coates' Between the World and Me and The Autobiography of Malcolm X. He also researched vegetarianism and adopted a plant-based diet.

"There's only so much music you can listen to while flying," Brogdon says.

David Zalubowski/Associated Press

Mindaugas Kuzminskas, a second-year forward for the Knicks, chuckles at the whole topic, considering these to be first-world problems. The 28-year-old, who is older than most of his sophomore peers, spent four years playing in various professional leagues in Lithuania and three years in Spain before signing with the Knicks last season.

"You get private planes, skip security," Kuzminskas says. "Compared to the way a lot of the teams do it in Europe, the travel here is easy."

Even though that part of his adjustment to the NBA was a breeze, the business end of things left him surprised. For example, he was thrown off by practicing with Carmelo Anthony days before the 10-time All-Star was traded to the Thunder.

"One day, the guy's here; the next, he's not," Kuzminskas says. "It's really different."

In the end, though, the action on the court—and how to improve and keep up there—occupies NBA rookies and grabs most of their attention.

"Having the endurance to keep up all year was the hardest part," says Knicks second-year guard Ron Baker. "That's the advice I give to [Knicks rookie] Frank [Ntilikina], especially when he was injured during training camp. The season's really long. Make sure you take care of your body first. There's plenty of time."

Even off days can become, in a way, grueling.

"In college, you're rushing from class to practice and then have to study," Ellenson says. "Here, though, you spend an entire day at the facility. I think that's what surprised me the most."

From treatment to ice baths to lifting to shooting to practice to, yes, even meals, entire days can be spent at a training center where the focus is on basketball and nothing else. Since some rookies lose more games in their NBA first season than they had across their entire basketball careers, that lifestyle can become even more grating.

Then there's the mental toll that comes from a change in standing.

"You come in as a rookie expecting you're going to play a lot," Hawks second-year wing DeAndre' Bembry says. "And for me, that just didn't end up being the case."

Bembry had grown used to being a star when he entered the league. He was a first-team All-State player as a senior at New Jersey powerhouse St. Patrick High School, was Atlantic-10 Player of the Year three years later at St. Joe's and was taken 21st overall in the 2016 draft.

Out of the billions of people in the world who play basketball, he was one of the nearly 500 good enough to be in the NBA. He was the 1 percent of the 1 percent.

Then his rookie season began, and Bembry suddenly found himself relegated to the end of the bench.

David Zalubowski/Associated Press

He'd receive texts from friends and family asking why he wasn't playing. For the first time in his basketball career, he began playing timidly and passing on open shots.

"Every rookie has their own story and was the man on his team when they were younger," Bembry says. "And then you get to the NBA and that's just not the case.

"You discover what it actually means to stay ready and how to take the opportunities given to you and make the most of them. That's stuff you think you know before, but you don't."

They think they know it because they enter the league on top of the world. Whether it's a demotion, harsh words from a coach or getting tossed aside by Blake Griffin, something will knock them off that perch before they can start making their way back up.

Yaron Weitzman covers the Knicks and NBA for Bleacher Report. Follow Yaron on Twitter, @YaronWeitzman, and listen to his Knicks-themed podcast here.