Heidi Klum

Despite putting on around 48 lbs, Heidi was back to her model self (in a thong, no less!) just seven weeks after her first son, Henry, was born. With the help of trainer David Kirsch, Heidi's regime included intense workout sessions and a diet similar to the 3-Hour Plan, which involves eating small meals every three hours.

The supermodel admitted that the regime involved lots of hard work: ‘I ate well during pregnancy - anything I felt like, even cookies, ice cream and fries. But with David I had to watch everything I ate. The exercises were really hard. I kept wishing that someone would train for me'