Some say that fasting activates "autophagy" which has great health benefits, supposedly being great for preventing the remission of cancer: https://en.wikipedia.org/wiki/Autophagy — but note that I could not find any concrete study or proof of it, this being anecdotal evidence from some clinics that advise their patients to do fasting instead of chemotherapy.
I practice fasting for 36 hours, 3 times per week. Monday, Wednesday and Friday I don't eat or drink anything other than water and coffee. You can go shorter, like one meal per day in some days or longer, e.g. 5 days is easy once you get used to it.
As a tip: eating high fat, low carbs meals before fasting helps. Also if you get dizzy or if you get cramps, you probably have an electrolytes imbalance and you need to stop your fast. If that happens to you, make sure to take salt (sodium) and possibly magnesium supplements. Once I started doing that, the dizziness and the cramps stopped. But document yourself first and consulting a doctor and doing some blood work might be good ideas.
This is a pretty good book on the subject: https://www.amazon.com/Complete-Guide-Fasting-Intermittent-A...