It depends on your internal (fat) reserves. I'm 58kg 1m83 (BMI 17.32), so I wouldn't really try such a long period. But there are days I eat a lot, I build some

It depends on your internal (fat) reserves. I'm 58kg 1m83 (BMI 17.32), so I wouldn't really try such a long period. But there are days I eat a lot, I build some glycogen reserves (easily available fat, made from glucose) due to my diet with much fruits, or other stuff like rice, honey, then the next days I can fast intermittently and use that glycogen. As a result I can't really gain weight, it always balance itself to that weight. I think people with more weight, have deeper fat, and it'll take longer to use it. I remember seeing an article that our ancestors possibly were hibernating. The more fat, the more time you can spend fasting, even on a dry fasting (fat holds water), but in that case it's important to limit physical exercise