Katie Holmes finds boxing ''thrilling''.

The 39-year-old actress has been in intensive training to star as an ex-Marine in 'The Doorman' and the brunette beauty has found throwing punches a great way to relieve the stress caused by ''mundane'' everyday life.

She said: ''I was a five-pound weight person, and now I can do 15, 20. And I've been doing a lot of boxing, which I had never done before. It's thrilling. You can get out the stress of the day. I just go in there and think of all the mundane things that bother me. Traffic! I put off all my calls till after boxing, because it puts me in a much calmer place.''

Katie wanted her workout regime to be ''authentic'' to her character, so was training for practical purposes, rather than thinking about her appearance.

She told the new issue of Women's Health magazine: ''I wanted to be authentic to a person who trained in the military. Which means someone who wasn't always paying attention to the mirror and who was in shape not for vanity, but because that's what her job called for.''

And the former 'Dawson's Creek' star - who has 11-year-old daughter Suri with ex-husband Tom Cruise - thinks it is important to stay fit and active to set a good example as a parent.

She said: ''Being a parent, every choice I make it with my child in mind. So part of getting in shape is to be an example.''

Katie eats a largely plant-based diet but will occasionally indulge in her favourite pepperoni pizza.

She said of her eating habits: ''It used to be about fitting into my jeans, and I'm so sick of that. Now I think of it more as a health decision.''

And the actress also enjoys the ''sense of community'' that comes with group workout classes such as SoulCycle.

She explained: ''Like, if she can do it, I can do it too.''