Isla Fisher says breastfeeding is the best thing to do to lose your baby weight.

The 'Great Gatsby' star has two daughters with her husband Sacha Baron Cohen, and she insists she didn't need to worry about how she was going to shift her extra pounds because nursing uses up so many calories.

In an interview with the new UK issue of HELLO! magazine, she said: ''I believe in the power of breastfeeding. I know some women say it doesn't help them lose the weight, but I think it burns an extra 250 calories a day.

''I breastfed for two years with both my children and by the end of that period I was back to normal. I swear by it. I've also been lucky in that I've been able to afford assistance with childcare, so I can go out for a run or a workout.''

Although Isla has been able to get her figure back she admits she relies on some extra help so she always looks great when she hits the red carpet.

The 37-year-old actress swears by the stomach-minimising power of Spanx to make her figure slender in any outfit.

Asked what her best-kept fashion secret is, she enthused: ''Spanx! Never leave home without them. You can't eat very much and they're restrictive like a girdle, but, hey, you look really slender and slim.''