https://aeon.co/essays/is-fasting-good-for-you-what-we-know-so-far

So what about the medical benefits? In the end, both throughout and after the fast, my blood pressure remained at exactly the same, slightly elevated level it had been before I started. So much for controlling it by fasting, at least for me. I lost 11lbs (5kg) over the week and gained 7lbs (3kg) back within three days. The other significant thing I noticed, as many others have too, was the reduction of libido to absolutely nothing. I had no sexual thoughts all week, which was not an entirely unwelcome (though thankfully temporary) break from the usual. I experienced a phenomenal increase in physical energy but at the expense of a lack of mental concentration. So if you need to lose some weight and also need to dig some ditches this week, fasting might be just the thing. On the other hand, if you are trying to solve problems in the theory of quantum gravity, it’s probably best to get some food down. These effects lasted only while I was actually fasting: one day after breaking the fast, I felt completely normal, with the same appetite and level of physical energy as usual. At this point, I should remind my gentle reader that my weeklong experiment had the grand sample size of one (two, if you count my wife) and so should be taken for what it is: just my personal experience of fasting, not a scientific study.