The rapid weight loss and regain is most likely because of the low carb approach.
When you eat few carbs, you burn off your body's stores of glycogen, appx 1 lb in an average person. When glycogen is stored, it binds water at a ratio of 4:1. So losing the lb. of glycogen means losing 4 lbs. of water. When you then eat carbs, your body overcompensates and stores more glycogen and water than usual.
Eat a balanced diet and watch the total calorie intake.
All the oddball diets won't teach you how to eat to keep the weight off.
"To give anything less than your best is to sacrifice the Gift."