Billie Piper admits she was "lucky" to lose her baby weight so quickly.
The svelte actress – who has a one-year-old son Winston with her husband, actor Laurence Fox – is pleasantly surprised the extra pounds fell off so easily because she's not particularly healthy.
She said: "I think I was quite healthy I wasn't massively healthy. I just ate loads of protein.
Billie joked: "It's either that or speed pills, and the thing is you do actually have to sleep at some point."
And Billie admits she counted down the days until the end of the pregnancy – when she could indulge in her favourite vices once more.
She told The Times newspaper: "I became completely neurotic and saw what I'd be like without booze and cigarettes. And it ain't pretty!"
Billie, 27, concentrated solely on Winston after he was born and admits she treasures the time alone the pair had together.
The actress – who can be seen reprising her role as a high-class prostitute in the new series of 'Secret Diary of a Call Girl' - said: "I'm actually grateful for that time now. It forced me to be in bed with my child. And really that was the only time that I was still, with baby, without distractions or confusion. It was just the two of us. You sleep when they sleep and feed when they feed."