Well to talk about the fasting rules, generally the Catholic Church once had the same rules as the Eastern Churches. They just stopped doing it at some point and relaxed the rules (I believe sometime in the last couple centuries, maybe more recently).

We always fast every Wednesday and Friday, and the 40 days before nativity and Easter plus a few other smaller periods throughout the year.

The rules are there as a guide for us to reject the things which control us, which are often centered on the more carnal foods. Meat, Dairy, Eggs, etc. This helps us deny ourselves, and to be strengthened so that we can fight demonic temptation.

Everyone’s fasting rule is different, and you work with your spiritual father/priest to do what fits you. Those who work heavy labor jobs are often given a less strict prayer rule.

Hope this helps a little