The 'My Heart Takes Over' star put on weight after undergoing surgery to have a cyst on her ovary removed in 2010.
Speaking to New, Wiseman said that she was shocked by the negative reaction to her fluctuating appearance.
"I went a full dress size bigger - from a size eight up to a ten, maybe even a 12," she revealed. "Everyone thinks I've tried to lose weight, but I genuinely haven't.
"I'm really getting annoyed reading that people are calling me fat! I'm a size ten, not 100! I'm human and curvy, get over it! It's boring!"
Wiseman added that she was hoping to inspire fans uncomfortable with their weight to feel confident about themselves.
"As a band, [The Saturdays] take pride in being role models to children and other young girls and I think that the best role model is someone who is comfortable in their own skin! And I am."
Wiseman is currently dating JLS star Marvin Humes, who has been tipped to propose over the Christmas period.
Watch The Saturdays in the video for 'My Heart Takes Over' below: