Sure it's sustainable ... unless you already have carb/sugar addiction. Not NO carb, but low carb. Just ask the Inuits who were initially studied by Atkins ... very little carbs in their diet yet extremely healthy.
No it's not. The science and personal experience of many people prove it's not sustainable. Doctor (F)Atkins died of heart disease and obesity. His diet plan didn't work out well for him. It killed him.
There's no such thing as "sugar addiction". Another falsity.
Let's go by our own experience.
What's your body fat percentage, Ladislaus?
What's your body fat percentage, forlorn?
Let's see how well your diets are doing you. I'm not talking about brief periods where you subject yourself to calorie restriction while going keto.
Btw, there is no calorie restriction with a high carb/sugar and low fat/oils/animal protein diet. High calories still result in low body fat, especially if you're physically active. The more active, the less body fat, all other things being equal.