No fat sympathy here, but while that is the exact mechanism that anyone who wants to lose weight MUST follow, the reason she gained it back is not because she doesn't understand CICO, but because what they do on that show is laughably unsustainable. It's a reason I hate "The Biggest Loser" and shows like it because they're only making the obesity epidemic WORSE. Hams see that shit and think, "Wow, if that's what it takes to be a healthy weight then I'll just stay fat!" They don't realize that you don't have to run marathon obstacle courses and eat tiny leaves of lettuce 24/7 to be fit. Just getting in a little daily activity as simple as light walking and still eating the exact same foods they're eating, but in more reasonable portions is all it takes. Because people waaaaaaaaaay overestimate how much they burn from exercise and waaaaaaaay underestimate the calories they take in, a massive overemphasis is placed on ridiculously rigorous exercise and not enough is placed on sustainable, enjoyable dieting practices.