Rob Kardashian's Weight Loss: The Gym Secrets That Helped Him Drop 40 Pounds

Rob Kardashian, Kris Jenner's reclusive only son, has long battled depression and weight gain, and hasn't been seen on the family's reality show, Keeping Up With the Kardashians for years. But since finding love with girlfriend Blac Chyna, he has dropped a whopping 40 pounds in short order. How did he do it?

“Rob’s favorite machine to lose weight has been the elliptical,” a source told HollywoodLife exclusively. “He has been on it every day trying to get in his low-impact cardio. He hates running on the treadmill.”

Although his famous family doesn't approve of his relationship with the 27-year-old model and former exotic performer, it seems to have done more good than harm.

“He has been eating much healthier with Blac, lots of chicken breast, fish and veggies," the source continued. "Besides the cardio, he has been doing some weight lifting, and Blac has even turned him on to yoga.”

If you want to look good and you want it fast, it definitely doesn't come cheap.

“They have a private instructor come in and teach just the two of them a couple times a week. He has lost many pounds but is far from his goal weight, the source says. “He is determined and disciplined about getting what he calls ‘college Rob’ back.”

Although Kardashian is not yet content with his weight, he's not so camera shy anymore -- he was spotted with Chyna running some errands last month.