I have read quite a bit about fasting and can see that there are benefits. There are books and books about the topic, and I am sure a Google search of the topic would yield many, many hits. Why am I saying things twice?
Fasting is a Biblical concept. I believe, though I am not sure, that a priest can call a fast of the congregation for some important undertaking of the Church. Get your Bible and in the Concordance there will be scripture references for fast and fasting. The fast for the Christian is to become closer to God and to prove that you are serious about your petition. Sustenance will be from God and not from the world. The disciples asked Jesus why they were unable to cast out a demon, and He told them that this kind takes fasting and prayer. During the Catholic observation of Lent, something that matters is given up for a period of time. It is not to be flippant like giving up liver when the person doesn't even like liver (who does?). Jesus spent 40 days on a fast in the desert and then was tempted by Satan with bread.
From just a health and wellness point of view, though, fasting is a way to cleanse the system and empty the liver of impurities and stored energy. A fast can be a good way to start a new way of eating. It can also be a way of getting back on track after slipping up. I have fasted for a day before but I know of people undertaking much longer fasts. If there is a health condition, this must be considered. A diabetic would probably have a problem with blood sugar on a fast but there are water fasts, juice fasts, or just a fast from a particular thing - like chocolate, sugar, soft drinks, eating after 6 p.m. You might look over what's available at Amazon. I usually get one that can be bought used - there are some used books that cost a dollar or less. Even with shipping it's still way less than new.
A fast might also be a way to prove to ourselves that we are in control of this body and not our stomachs or the mind games that we play to excuse if and when we eat.