England opener Dom Sibley has lost 12kg after receiving a "wake-up call" on the aborted tour of Sri Lanka in March.
"Training in that heat, I saw some of the lads running after a big session and it was a bit of an eye-opener for me," said the 24-year-old.
"I was sitting on the plane home thinking that I needed to do something."
Sibley will play his first home Test when England begin their three-match series with West Indies on Wednesday.
The Warwickshire batsman averages 40.22 from six Tests, having made his debut in New Zealand in November.
He was due to play in Sri Lanka, only for the two Tests to be cancelled because of the coronavirus pandemic.
However, a player previously nicknamed 'The Fridge' learnt more about the demands of international cricket on that tour.
"For the first time in my career I felt a little bit self-conscious about my physique and my weight," Sibley said. "I was probably carrying too much weight.
"I saw how fit some of the guys are, especially the senior guys, and how impressive they are in their training."
Sibley said his weight loss is down to a mixture of diet and training, saying he has not done anything "drastic".
In the first Test against West Indies he will resume his opening partnership with Rory Burns, which was broken up in South Africa after Burns suffered an ankle injury.
"I've always been someone that hasn't been the fittest in the squad," Sibley said. "Whether it's been at Surrey or Warwickshire, I've always been coasting a little bit in that aspect.
"I've had taps on the shoulder before, but I haven't done anything about it. It was probably a bit overdue, me having that wake-up call.
"I don't feel much different. People have said I look different, which is obviously nice. Regardless of whether it leads to runs or not, it was just something that I needed to do."
