The person I’m supporting for weight loss surgery had to be on a practically 0 carb diet because it shrinks your liver, so it gets it out of the way for the bariatric surgery. She actually lost a lot of weight on the almost-0 carb diet. It wasn’t balanced, though, and she had to take vitamins. She couldn’t eat fruit on the diet. She lost so much weight on it, though, that she was in danger of losing her approval for the surgery. They told her to add a few carbs like potatoes, and to eat a lot of cheese to keep up her calorie intake. So really, it wasn’t a diet sustainable in the long term, but it is probably modifiable so that someone who was not as overweight as she was, and just needs to lose, say, 40 pounds, not close to 200 (which is where she started-- it’s more like 150 now), could lose weight on it and keep it off.
My brother has struggled with his weight, and for him, the “trick” is not to snack between meals. He eats as much as he wants for meals, including seconds, and has dessert at dinner, but he never eats anything outside of his three meals a day except coffee with artificial sweetener, or diet drinks like Crystal Light. He isn’t skinny, but he keeps his BMI in healthy levels for his age, and he looks good. He also keeps his blood pressure under control. When he let his weight get up a little a few years ago, his blood pressure started to go up, and he got worried, because our father had HBP, and was on medication starting in his late 30s until he died. By keeping his weight down, and avoiding salt, he has stayed off HBP medication. I know salt is not considered as bad as it once was, but for my brother, it seems to make a difference.