The White Days
The Messenger of Allah, Mohammed is teaching His disciples: “It is sufficient for you to fast three days every month, because for every good deed you will have (the reward of) ten like it, so that will be like fasting for a lifetime”.
The white days refer to the 13th, 14th, and 15th of the lunar calendar. The days are named as such due to the moon being full and the light it reflects is at maximum.
In Bible;
Matthew 6:16, where Jesus is teaching His disciples basic principles of godly living. When speaking on fasting, He begins with, “When you fast,” not “If you fast.” Jesus' words imply that fasting will be a regular practice in His followers' lives.
Science;
Fasting for as little as three days can regenerate the entire immune system, even in the elderly, scientists have found in a breakthrough described as "remarkable".
Although fasting diets have been criticised by nutritionists for being unhealthy, new research suggests starving the body kick-starts stem cells into producing new white blood cells, which fight off infection.

In my opinion, fasting was invented as a way to make the common people happy with being hungry. Let's make sacrifice and having less a positive aspect, so there is more to give in the collection plate to the religion.

If organized religion was really concerned with starving children, poverty, people not having clean drinking water and combating disease then perhaps they should sell off some of those priceless artifacts and precious items and use that money to do more than just offer lip service or make token gestures. How many children can be fed with one gold chalice when you can "for just 63 cents a day, fill empty stomachs with nutritious food—and save children's lives" (care.org)? How many villages can have life-saving water brought to them by selling one tapestry?

Perhaps after 2000 years of organized religion, through various sects and beliefs, it might be nice to have ALL of the alms for the poor actually make it to them rather than the religious leaders and their organizations.

Organised religion is about controlling the unwashed masses.
Nothing more. Nothing less.
It has nothing to do with justice, morality, or the good of humanity.

A relationship with Jesus is why some fast for Spiritual strength.
It's also not organized religion. Not about Works.

i read one of the posts, fasting
you do that in private.

also about famines etc, read Mathew 24.
if you can understand it.
few can