Weight is lost by having a caloric deficit.
Eliminating an entire food group or the majority of it is just a different way of achieving that caloric deficit.
My question is: is it sustainable?
If not, then should you do it?

Since I have Celiac Disease, I've been pretty close to Keto for many years now. Most of the time I am low carb/healthy fats (approx 75-100g/carb/day. Some days I am Keto (below 50g), and some odd days I fast. Almost always 16:8 (2 meals/day). I know quite a few people who do very well on Keto, but they are doing it the smart way and eating healthy unprocessed foods, and not adding extra fats for the sake of it - thinking more is better. I do feel more physically satisfied on higher calories if they are mainly fats and proteins. Even healthy fruit and legumes can cause me to feel hungry again in a short period of time, so I limit them. I have a friend in her 50's who is carnivore (strict eggs/fish/meat - with herbs & spices.) She found that this 'ultimate' AIP way of eating made her leaner and solved many health problems her endocrinologist, rheumatologist, and general practitioner couldn't seem to figure out, while increasing her energy, stamina, and strength. She runs and plays golf regularly again. I don't think I could handle carnivore myself, but if pushed by health, maybe.