The mother-of-two took on the challenge in honour of her former co-star, Barbara Windsor, who was diagnosed with Alzheimer's in 2014.
She finished the marathon in an impressive five hours and 27 minutes and documented her training in the run up to the race.
Posting on Twitter, Natalie explained she ran 18 miles in just one day as preparation.
Running can burn around 600 to 800 calories per hour which means her intensive training routine is sure to have helped her lose a few pounds.
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Since the marathon, it seems Natalie has kept up the healthy habit and recently posted about her love for running.
A post on Twitter said: "On gloomy days like this running will make you feel so much better!
As well as regular exercise, Natalie is sure to have fuelled her training with a healthy diet.
In 2018, she told Now magazine: "After playing Sonia in EastEnders for 12 years, I thought itd be good to change my image.
She told Heat magazine: "I really wasn't well. I was bordering on having an eating disorder.
"There were nights I would go out for dinner and then I'd go home and take laxatives because I didn't want the food inside me.
Despite struggling with her weight in the past, she has since overcome this to develop a healthy lifestyle.
Additional information and support on eating disorders can be found on the NHS website or at B-eat.
See the article here:
Natalie Cassidy weight loss: EastEnders star shed whopping three stone with simple trick - Express
