How long do scientists believe a person can live without food?

I sometimes wonder about the homeless people and think about when was the last time they ate anything.

Scotsman Angus Barbieri is on record for fasting for 391 days, loosing over 19st in weight.

correct me if I am wrong, but during the third Reich, the SS did perform starvation games on prisoners. to see the duration those who could go the longest without eating