The 25-year-old singer has made some big lifestyle changes as part of a fitness drive amid the coronavirus pandemic, and he doesn't want to be "mashed up" on stage.
He told The Sun newspaper's Bizarre column: "Through lockdown I didn't drink, I stopped smoking, I've got fit.
"I'm trying to get my mind as healthy as possible and be the best person I can be.
"I couldn't go on stage and I couldn't function properly with a mashed-up head. I just couldn't do it."
The changes come ahead of a virtual show he's playing at London's O2 Academy Brixton on October 2.
He's also been working hard on his upcoming second album, which follows his debut 'Lighting Matches' and deals with the impact his success had on his relationship.
Tom admitted his own ego caused the breakdown of a recent romance, and much of the new record - which is set to be officially announced and named at next month's gig - will deal with the split.
He said: "I just thought the sun shone out my a*** for a minute. I forgot about the real person who loved me for me.
"I ended up blaming loads of things on this girl and unfortunately I was probably the toxic one in the relationship."
The 'Oh Please' singer previously revealed he was doing his best to eat no dairy and meat products over summer, but it wasn't easy, as he slipped up on the first day by chowing down on some chicken wings.
Asking his fans for some advice on how to go vegan, Tom said on his Instagram Story back in July: "Today I was going to go vegan, but I didn't because I ate some chicken wings.
"Soz, but tomorrow I'm going to start a vegan diet so if you've got any tips or recipes, send me them over, because I want to challenge myself to a vegan diet.
"I want to do it for a week. If I like it, two weeks, three weeks, four weeks, so on, so on."