ENGLEWOOD, Colo. -- In order for San Francisco 49ers running back Mike Davis to let go of a disappointing rookie season, he had to part ways with something he loves: Flamin' Hot Cheetos.

And it wasn't just Cheetos. Davis said during the offseason he made a concerted effort to change his diet completely. He named chips as his primary vice, opting to cut them out altogether, along with fried foods. He switched to fresh fruit as his preferred snack and returned for training camp in much better shape than he left.

But make no mistake, it was those salty chips that were the hardest to say goodbye to.

"That was like a heartbreaker," Davis said. "Man, my favorite chips were hot Cheetos and I haven’t had those in months. I have just got to stay away from chips. No type of chips at all, I’ve got to stay away from them."

Mike Davis ran for just 58 yards as a rookie, averaging 1.7 yards per carry. John Hefti/USA TODAY Sports

Although the sample size is small, Davis' ability to avoid chips also paid off in evading Houston Texans tacklers in the preseason opener. Davis rushed for 72 yards on five carries, including a 44-yard burst on his first attempt. In just those handful of carries, Davis looked quicker and more elusive than at any point in his rookie season.

After the Niners used a fourth-round pick on Davis in the 2015 NFL draft, he never was able to get on track. He battled a broken hand that limited him to six games, but even when he played he was mostly ineffective. Davis finished with just 35 carries for 58 yards, an average of 1.7 yards per attempt. When he entered his first NFL offseason, he knew he needed to make some changes.

But this isn't the typical "player lost X amount of weight and is in the best shape of his life" story. No, Davis said he actually weighs more than the 217 pounds he was listed at in 2015. He's just turned much of that weight into lean muscle.

"People think I got real light for some reason," Davis said. "I actually gained weight. I just got a little more lean so [coach] Chip [Kelly], with as much as we run, he wants us to be in the best shape."

The result is a player better equipped to make himself small through the hole and juke a defender in the open field.

“He’s been doing a really good job and Mike’s coming along," offensive coordinator Curtis Modkins said. "He’s one of those guys that are up, up, up, up. So, every day he’s getting better and better and he had some really decisive runs. Hopefully that will continue. I think it will.”

Davis did more than just cut out unhealthy foods. He also spent the offseason working out at Exos training facility in Los Angeles with Rams running back Todd Gurley and a few other NFL players. On the mental side, he focused on learning the ins and outs of Kelly's offense. Davis said Kelly's offense is similar to what he ran in college at South Carolina.

That's made for a seamless transition and an opportunity for Davis to wipe the slate clean from a year ago when, despite his best efforts, he was unable to avoid hearing some of the criticism thrown his way.

"I didn’t let in much, but you know, some stuff you can’t help but see," Davis said. "But I didn’t let that type of stuff get to me. I just wanted to come out here and do great things for my family. My motivation is to help my family out. That’s the main reason I’m here. Struggling growing up as a kid, I wanted to make sure everybody in my family is good."

As it stands, Davis still has plenty to prove. One strong preseason outing does not a player make. Davis currently sits behind Carlos Hyde and Shaun Draughn on the depth chart, but Kelly said after the Texans game that Davis has put himself in position for a spot as the third running back. General manager Trent Baalke also expressed his optimism about Davis, referring to him as a rare three-down back in today's NFL.

Davis has three more preseason games to solidify his case. And now that he's conditioned to be faster, he has no intention of slowing down.

"I feel great, being able to open up more and [be] more powerful, there’s a lot of things that factor in but as a rookie sometimes you don’t feel as comfortable," Davis said. "So now you know [what it's like] once you get that confidence, it’s all about having that."