My oldest brother lost over 50 lbs doing low carb a year or so ago and has sadly gained quite a bit back. In his case, I think it's about education. He went to a nutritionist (dietician? I'm not certain) and she placed him on this diet. It was handed to him and he went with it; he didn't understand why it worked or what to do to maintain it. Now he wants to know what I'm doing and I've tried to explain it to him but he simply doesn't seem to care about the why. Makes all the difference, I think.
Mordor Challenge : 73 miles