is exercising in the middle of the night to shed her post-baby weight.The Latino singer, who gave birth to twins Max and Emme in February, is reportedly losing up to 10lbs a week by getting up at 4am and hitting the gym in a bid to regain her famous figure.A source told Britain's Closer magazine: "Jennifer has always been a workaholic and she has applied the same attitude to her post-pregnancy regime. Because raising twins is so demanding, she gets up at 4am to fit it all in."She spent the last month of her pregnancy planning her regime with a team of nutritionists and personal trainers. She calls them her 120lb team in reference to her target weight. She is working out for three hours a day, seven days a week."Jennifer, who is married to singer Marc Anthony, is also believed to have cut all carbohydrates from her diet and is surviving on 1,400 calories a day. She is eating only high-protein steamed fish or chicken and fresh vegetables.The source added: "Jennifer doesn't allow herself any sugar, caffeine or alcohol and she only drinks purified water."