07/01/2011 09:27 GMT | Updated 22/05/2015 06:12 BST

The Celebrity Metabolism Myth

On stage and burning through those calories! WireImage

How frustrated do you get when a celebrity tells your favourite magazine that they maintain their perfect figure – or effortlessly return to their pre-baby weight weeks after giving birth – through a magical combo of eating whatever they want and never exercising. I hear your angst and let me tell you, their fitness regime might not involve three-hour gym sessions but celebs get their fair share of exercise in just doing their jobs.

When I was doing my pop music thing I would never exercise but I'd be rehearsing for shows, learning dance routines for videos and doing 18-hour video shoots. Those marathon-type activities burn a lot of calories and that kept me in shape.

Chris Brown's Yeah 3X is a great example of the rigours of music video performance!

Actresses can be on their feet all day constantly repeating the same moves take after take. Models are asked to pull this way and twist that way to contort their bodies into almost yoga-like poses. They might look casual and relaxed but in reality they're tensing every muscle. Sure they might not burning up the treadmill, but photo shoots can be three days back-to-back. The Marks & Spencer Christmas commercial was five days of dancing! Believe me, the physicality of 14-hour workdays like that counts as exercise, even if we weren't decked out in Olivia Newton John-style Lycra Physical-style.

The biggest challenge for working women these days is that in many cases the physical side of work has disappeared. In the olden days we had posties who walked everywhere so they were fit. Today they get about on motorbikes!

I know you've heard it all before but the best advice really is to fight the sedentary workplace by building exercise into your day-to-day life. Take the stairs, get off the bus or the tube a few stops early and walk to work or make yourself get up from your desk at lunchtime and take a 20-minute power walk around the block.

Trust me, I didn't shift my baby weight with a magic metabolism or faddy diet plan. I moved into a house with stairs and I run up and down them all day long taking care of Kris and Ethan. It works!