Jessica Alba shops with her mother Catherine Alba in Beverly Hills, a month after giving birth to aughter, Haven Garner Warren. The Spy Kids 4 actress, 30, gave birth to her second child, daughter Haven Garner, on Aug. 13. So how does she look so great?

US Weekly Reports:
“I did my first day of workout since I had the baby,” Alba Tweeted Aug. 30. “Just cardio for 40 minutes.”

The svelte star explained that she got the A-OK from her physician. “My doc told me I could start after 2 wks,” she wrote. “I’m going light, stationary bike and elliptical.”

The second-time mom (she and husband Cash Warren also have daughter Honor, 3) offered advice to others on Twitter about post-baby diet, too. “I would keep your diet as healthy as possible 6 days a week and give yourself one day to indulge.”

Other Alba-approved post-baby fitness tips? “Start with walking and throw in 3 sets of lunges 20 per leg. Your could do it while strolling your baby.”