Kourtney and Kim Kardashian Spill ALL Their Diet Secrets (Including a Weekly 24-Hour Fast)

Kourtney and Kim Kardashian are proud of their famous physiques, and any Keeping Up With the Kardashians loyalist knows it. On a recent episode, Kim shared that she'd whittled her waist down to 24 inches. For her part, clean-eater Kourtney (who's about five feet tall) spilled that her weight was less than 100 pounds. So, what do the sisters do to stay so svelte? Let them break it down for you. 

On her app, Kim wrote a post entitled: "How I Get a Flat Stomach." (The lady gives her fans what they want!) "It's so important to work out your core!" Kim shared. "My trainer Melissa and I have been doing really intense ab workouts — and even though they're SO hard, I love the end result."

Here's what the routine consists of: four sets of 20 leg lifts, four total minutes of planks (with 30-second rest periods in between), four sets of 10-rep ab rollers, and four sets of kneeling crunches using the rope on a cable-fly machine. It's a bit hard to imagine, so take a peek at the trainer demonstrating some of that ab work here.  

If you think Kim's workouts some grueling, just wait till you hear about Kourtney's diet. The petite reality star goes through periods of following the keto plan. "Once I knew the ground rules, I was very strict and really stuck to it," she wrote on her app. "I ate minimal carbs and no grains, beans, or legumes. Instead, I focused my meals on fresh vegetables and lean proteins." And, that's not all...

"Intermittent fasting is also a part of the keto diet," she shared. "For me, this meant not eating for 14 to 16 hours after dinner. I wouldn't eat past 7 p.m. at night and then I would wait to eat breakfast the next day until after my morning workout, which would be around 10:30 a.m. to 11 a.m. Then, one day a week, I did a 24-hour fast where I only drank homemade bone broth, water and green tea." 

Extreme routines, extreme physiques.

Any health-related information is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a physician or other qualified health provider for any questions you may have regarding a medical condition, or before embarking on any diet, exercise, or wellness program.