Maybe you should start with shorter ones and increase the duration gradually (assuming you're interested in the benefits of intermittent fasting, of course). Th

Maybe you should start with shorter ones and increase the duration gradually (assuming you're interested in the benefits of intermittent fasting, of course). The human body is quite well adopted to the prolonged periods of fasting and has resources to support itself for literally weeks without food (it is not an advice to starve oneself for weeks, just a note to show that 40 hours is quite a short period). The longest I ever did was 72 hours, and I only did this once, but without any noticeable negative effects. I noticed also that the most discomfort was psychological - when the time to eat comes and goes, and I did not have anything, I felt more of a psychological need to eat, rather than physical. Also, the 2nd and 3rd day were way easier once I got a bit used to the fact that I'm not eating when I'm supposed to.