Oprah is the last person I would look to for advice on how to maintain a healthy weight. Not that I disparage her many attempts, it's just that she has never given the LCHF platform any airtime on her shows and that seems highly suspect to me.
Just reading Gary Taubes Why We Get Fat where he illustrates the history of "diets" or scientific study on obesity is sketchy at best.
Why has Oprah never pursued LCHF? Because there's no money in it.