"In Zoroastrianism or Mazdaism, however, fasting has been implicitly rejected throughout the faith’s history. Zoroastrian doctrine perceives no disjunction between spirit and matter along lines of good and evil; rather, it regards both as essential for achieving piety and both as susceptible to unrighteousness. Hence, Zoroastrians believe that the body should function as a means by which the soul can fight evil and regard any action that physically weakens the body as sinful. Moreover, sex is viewed as essential for procreation which brings more believers into the world. Standard or Young Avestan texts such as the Vidēvdād (Avesta, ed. Geldner, 3.33, 4.48, 7.70) emphasized that eating was essential for life, claimed consumption of meat enhanced spiritual perception, and suggested hunger and thirst caused much suffering. Pahlavi commentaries continued this anti-ascetic theme, stressing the notion of moderation or paymān between gluttony and privation in partaking of food, drink, and sex. Piety was said to result from not fretting about moderate consumption, and deviation from this mean was equated with concupiscence (Dēnkard, ed. Madan, pp. 267, 295)." https://www.iranicaonline.org/articles/fasting
Then Mani came along, introduced fasting. It was the main rival to Christianity before Islam came along. Both Islam and Christianity are heavily influenced by Mani and vice versa. https://en.wikipedia.org/wiki/Manichaeism