But the trip to Houston isn't an easy one, and by day four, Shantel's pain becomes so unbearable that Dr. Now has to meet her and Carlton at a nearby hospital mid-way. 

Upon seeing them, Dr. Now cautions that the brother and sister are in a "very serious situation" and have "a lot of work to do to make a difference ... before it's too late."

"It's a matter of life and death, you need to understand that," he sternly tells Shantel and Carlton, cautioning them about being each other's enablers.

While the two initially have a rocky start losing weight and don't get approved for surgery on their first check-up, seeing therapist Lola Clay seems to work wonders for their progress.

By the siblings' next weigh-in a couple of months later, both Carlton and Shantel lose over 130 pounds: he loses 132 and she loses 136. And while both they and Dr. Now are relieved with the massive strides they've made, the famed bariatric surgeon voices his concerns about their co-dependency once again, given the fact that they've lost almost the exact same amount of weight. 

"I'm very proud of Shantel and Carlton," he says nonetheless. "They've worked very hard these past months and have shown me that they're taking this opportunity to change their lives very seriously."

Ultimately, this leads Dr. Now to approve the siblings' weight-loss surgery.