The Manchester United left-back is set to win his first cap in 18 months when the Three Lions face Spain and Switzerland over the next week.
Shaw's fitness has been question throughout his United career but he has been given the nod ahead of Ashley Young for his club and country.
When asked what he put his resurgence down to, Shaw said: "You guys will probably know because it's always in the news… Fizzy drinks.
"People say I was a fizzy drinker and a snack eater. It wasn't true.
"I've changed massively on and off the pitch. I've matured, grown up. I've gone from a kid to a man now, and I know what I need to do to push myself.
"The nutrition side… I've not made massive changes because I was always looking out on that side, but I've cut out some of the silly things I was doing.
"I've seen a psychologist, but for the last four years. Especially after the leg break: that was a very tough time.
"A lot of the stick I've had in the last two or three years has pushed me on. I didn't need to speak to anyone about that. I just needed to see it myself
"I'm just training as I always have. I'm a hard trainer, wanting to improve every day. There weren't many chances last season, but I've started this season off and played four times.
"I've not done that often enough. It's great to have my fitness back and to look forward to the season.
"I want to play for Manchester United, to stay there and fight for my place, and prove my worth to the team. I want to do the same here now and give Gareth (Southgate) a headache over selection, and choices."
Shaw made just 43 appearances for United is his first four signings – including 11 in both of the previous two under Jose Mourinho.
The United boss has continually called out Shaw since arriving but the former Southampton man appears to have won him over.
Mourinho made a point of putting his arm around Shaw after the 3-0 home defeat to Tottenham last Monday.
When asked if he had bonded with Mourinho, Shaw replied: "A lot. Like I said, it was a very tough two years.
"Mentally it made me come out the other side and made me stronger, to want to prove to him that I can do what sometimes, in the last couple of seasons, he'd said I couldn't.
"At this stage I'm feeling positive and really good, and focusing on what's to come. Keep doing the things right, training hard. That's it.
"(I feel) very honoured and privileged for getting selected (for England).
"It's a really good vibe and a good place to be, coming off the World Cup. I'm looking forward to it."
Adam Lallana has picked up a groin strain and joins Raheem Sterling in having to withdraw from the squad.
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