I'm intrigued with and fascinated by cultures and religions where fasting is a core principle.
This is where it is no longer necessarily an individual choice (although it is always sold as such) but a collective one, enforced by the wider culture & society.
Islam, obviously, with Ramadan/Ramazan.
Fasting - or, observing the fast - during Ramadan/Ramazan is one of the "five pillars" of Islam. I have experienced Ramadan in three different Muslim societies in three different continents. Interesting, to say the least.
Then, there are the older forms of Catholicism, where, prior to the reforms of the Second Vatican Council, the two great fasting periods in the Catholic Church - Lent and Advent - each of 40 days duration - preceded two of the great Church Festivals, namely - and respectively - Easter and Christmas. In Catholic cultures, these fasts (prior to the reforms of the Second Vatican Council) used to be strictly enforced, as was the prohibition on the consumption of meat - or copious consumption of food - on Fridays.
These days, Orthodox Christian societies (Greece, Russia, the Balkans, the Caucasus) place considerable emphasis on fasting during Lent and Advent. Actually, their fasts are progressive - that means that more and different foods are prohibited - in addition - each successive week as the fasting period progresses - and are quite demanding; again, I have observed this taking place in the Caucasus. Restaurants - to my astonishment - had what they termed "fasting menus".
And then, there is the version of fasting in Ethiopia: There, not only are the great fasting periods (Lent and Advent) observed (and strictly), but in addition, every Wednesday and every Friday are also - still - recognised as fasting days.
Culturally, while the emphasis has long been on personal and individual strength, there may have been additional reasons for seeking to promote a culture or tradition of fasting.
Historically, in times of scarcity of food, (such as spring, when the winter stores might be running low), it made sense to try to persuade people to eat less (and share more) and reinforce that with the power of religious teaching; if appeals to generosity - and logic - fail - fear may work.
Likewise, in poor countries - where scarcity was a permanent feature of life, poor harvests, climate horrors, - fasts of a communal nature, religiously policed and enforced, made total sense. The population, somewhat thinner, may have survived, but famine may have been averted.
And there is a school of thought - which I first came across when reading material on Ethiopia - that argues that fasting on a more or less permanent basis (and yes, Ethiopian famines are notorious, but their fasting regime is unusual for its extent, severity and duration - people end up fasting for around a third of the year) serves to weaken the population, focus them on survival, and thus render them less likely to challenge authority, irrespective of whether it is secular or religious, as they simply may not have the time or energy to wish or want to do so.