Eating low carb and switching to high carb will cause significant water weight increase due to increased muscle glycogen. On the order of 5-10lbs. It's not fat.
But if I continue to eat high carb, there is a weight gain that is much harder to shed.
We humans in rich countries eat ad libitum. Any dietary intervention that helps us feel less hungry will lead to a reduction in the calories we consume.
Read Taubes for references to the scientific literature.
This does not happen with protein and fat consumption. If you force yourself to overeat those foods in the absence of carbs, which is not easy, they will be simply eliminated.
What you're referring to (excess carbohydrates converted to fat) is denovo lipogenesis which is exceedingly inefficient and rare in humans.
You can't get fat on a diet that is strongly deficient in carbs, while it's easy to get fat on a diet containing high proportions of fat and carbs.
The Eskimo subsist on meat and blubber alone. Roald Amundsen ran the experiment on himself and confirmed it.
The ethiopians have a diet of mostly carbohydrates (>70%), and are extremely lean.
Taubes is a bullshit artist who cherry picks data to sell books.
Ethiopians are hungry.