Can u surive 40 days with no food but with water?

water yes

food no

with food, it depends how big you are, if your a 700lbs that want to lose wait, your will look like a chicken when this transformation is over but also dangerous

Yes, most people could survive that long. Most people would be suffering from significant malnutrition by that time, though.

The IRA activists that starved themselves to death, took around 60 days to die.

I have read that, drinking water, the average person can fast 28 days with no bad health effects; but they have to start eating again gradually, so as not to upset their digestive systems. If you don't eat and take only water or fruit juice, your desire for food gradually declines until you just don't feel hungry at all, after a couple of weeks or so. Time to start eating again is signaled by the sudden return of hunger.

If you don't start eating then, you will get some ill effects, but will not die for some time yet. How long you can go without eating depends on the individual.

I did this once, and went only 21 days before the return of hunger; but then I'm kind of small.

Yes, but I wouldn't recommend it.

david blaine did it :)