The Tipperary singer is the most followed Irish female on twitter with 772,000 followers. Niall Horan is most followed Irish male with more than 16m followers.
In an interview with next month’s Cosmopolitan Body, the Saturdays singer said she has had to learn to ignore hurtful comments from anonymous trolls.
Una said: “It’s not easy to read nasty comments online but myself and the other Saturdays try not to take any notice of the negative remarks — you just have to block them out.
“We do look at and appreciate our fans’ positive feedback though.”
The frequently photographed singer said her stardom as one fifth of one of the biggest girl bands in Britain and Ireland does motivate her to keep in shape, but she also stays fit to help her sing during dance routines.
She said: “When you’re on stage you know you’re going to be photographed and that people are going to pick up on what you are wearing, what your legs look like and what shape you’re in.
But while I want to look good, I also want to sing well. It’s important for me to build up my lung capacity so I’m not out of breath when I’m singing and dancing on stage.”
The former champion swimmer, who is one of the celebrity contestants on ITV’s diving show Splash, said she hopes her daughter Aoife Belle inherits the sporting genes of her famous parents — Una’s husband is rugby union player Ben Foden.
She said: “I’m hoping Aoife will take after Ben and me when it comes to sport. I was very active as a kid. I used to swim competitively growing up and, like me, Aoife has no fear of water. Ben’s very sporty and speedy obviously so I think she’ll be quite fast on her feet. I will definitely encourage her to do sport as it’s great for building confidence.”
While Una admitted she was very broody after having her daughter she said she is no immediate rush to add to her family.
She revealed she got back into shape very quickly after Aoife was born with the help of a food delivery service but it is the only time she has ever had a meal routine.
She said: “I just eat well and avoid bad foods. I don’t do diets. The only thing I tried was a food delivery service six weeks after Aoife was born but I found myself adding extra carbs to the meals to bulk them out.
However, she said she believes new mothers should not try and lose the baby weight overnight like some celebrities.
She said: “I had a healthy weight gain of two stone during my pregnancy so I shed the weight naturally and quite quickly after Aoife was born.
“I’m back to my pre-pregnancy weight now. I fluctuate around 8.5 stone, although only ever by a few pounds.