Kim Kardashian's 50

Getty Images If you were shocked by Kim Kardashian's infamous butt selfie, that was kind of the point. Kardashian told Jay Leno that the Instagram snap seen 'round the world was a big 'Eff you' to the online tormentors who blasted her body while she was pregnant with daughter North West. 'It really hurt my soul. It changed how I am in the public a little bit,' says Kardashian. The reality star also revealed that four months after giving birth, she dropped her 50-pound pregnancy weight in a non-celeb-y way: Old-fashioned diet and exercise. Specifically, the protein-rich Atkins plan, paired with Barry's Boot Camp and Pilates Plus. 'A 50-pound weight loss in four months sounds sensible because it equates to 2-3 pounds per week,' Hilda Hutcherson, MD Clinical Professor of Obstetrics and Gynecology at Columbia University Medical Center, tells Yahoo Shine. She adds that women automatically drop about 12 pounds after childbirth just from the baby being born and losing amniotic fluid and blood. Moms can blast another 300 to 600 calories daily through breastfeeding, but Hutcherson says you can't get skinny solely through nursing. 'Breastfeeding can be exhausting and new mothers should maintain their strength by eating healthfully and often,' she says. The average woman who doesn't have much time or financial resources (nanny, personal chef, dietician, baby-handler), according to Hutchinson, needs about one year to fit into her pre-pregnancy clothes. This isn't the first time Kardashian dropped pounds using the high-protein eating plan. 'Kim had done Atkins once before with her father, so we gave her the information she needed to start,' Colette Heimowitz, Director of Education and Research for Atkins Health and Medical Information Services, tells Yahoo Shine. 'While I can't speak directly to what Kim did, new mothers like her should begin at the less-restrictive phase 2, consuming no less than 1,800 to 2,000 calories per day.' Long dubbed 'the bacon and eggs diet' for its emphasis on low-carb, high-protein food, the four-phase eating plan does permit whole grains on a limited basis. However, in phase two, carbs should be consumed by eating fibrous fruit and vegetables, says Heimowitz. The majority of the diet is composed of lean protein such as poultry and fish, and healthy fats such as nuts, avocado, beans, and seeds. Recommended snacks include turkey roll-ups, veggies and hummus, and Greek yogurt with blueberries. Kardashian also told Leno that she's been hiking with 'anyone that would go with me.' Walking uphill - nothing strenuous - is smart, as long as women start slowly, Hutcherson says. It's unclear how often Kardashian attends Barry's Boot camp, a high-intensity cardio-strength training combo referred to as 'drill sergeant tactics and a night club party atmosphere.' She and Kanye West were spotted walking on side-by-side treadmills and circuit-training together. The reality star also regularly hits Pilates Plus classes for 50-minute low-impact sessions, where she completes 20 to 30 reps that utilize her core on a machine called 'The Megaformer.'Considering Kardashian used to plug Quick Trim diet pills and was rumored to eat corn one kernel at a time, the new mom has come a long way!