The 32-year-old pop star - who found fame in 2002 alongside Cheryl Cole, Nicola Roberts, Kimberley Walsh and Nadine Coyle - even felt that dropping the pounds made her look older than she was.
Speaking to Mail Online, Sarah recalled: "I was too skinny when I was with the girls, it was ageing."
She has now taken up juicing as a way to stay healthy and regularly blends spinach, avocados and any other fruit and veg you can think of to create smoothies and juices, which keep her full and feeling fit.
Although she still enjoys some Skittles and sweets every now and then too!
Sarah hinted at her juicing obsession last month by posting a photo of her kitchen top covered in green goodies.
She captioned the picture: "Just another morning workout! #juicing #juice #healthy #green #yum #feelgood #greatstarttotheday."
As well as mixing up vegetable drinks at home, the pop star has also been busy working on some new music for her fans now that Girls Aloud have split for good.
Earlier this week, Sarah - who received treatment for depression and alcohol dependancy in 2011 - said she found the experience of recording a solo album therapeutic.
Speaking on ITV's Lorraine, she said: "I've been working on [the album] for about four years on and off. It's been really cathartic."
She added that her new tracks will sounds a lot different to the songs she made as part of Girls Aloud.
"I'm not an expert, so I have had a little bit of help with songwriters. I've gone with things that are very apt and speak volumes about who I am as a person," she added.
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