Greek writer Xenophon (c 430 - 354 BCE) notes in Cyropaedia, the biography of King Cyrus the Great (r. c 559-530 BCE), about the meal-related training provided by early Achaemenian era Persian schools to their children.
According to Xenophon, as part of their instruction in self-control, Persian children were taught to control their hunger and thirst (Cyropaedia 1,2.8). Their meal was – if the Athenian Xenophon will excuse this metaphor – Spartan. The Persian principles of partaking in a meal included self-restraint, modest fare and moderation. The Persians believed the early training in self-restraint led to fortitude against gluttony as adults. The teachers led by example and were themselves paragons of the principles being taught. Food was not eaten outside of the lunch period called by the teachers. The students did not withdraw to satisfy their hunger until their teacher gave them the sign for a meal break, at which time the class ate lunch together with their teacher in attendance. The lunch (tiffin if you will) the children brought to school from home consisted of simply bread and cresses (according to different translations, the relish of cresses included herbs and nasturtium). To slake their thirst the students brought a clean water cup which they filled by dipping into a channel of running water.
Xenophon notes in Cyropaedia 2.16 that the Achaemenian Persians also worked off by exercise what they ate. The reference here probably means that the Persians did not eat gratuitously but rather what they needed to stay fit. Since, they worked off by exercise what they ate; they would have been fit and not fat.
When the children grew older, they accompanied the king on hunting expeditions that in themselves training in discipline. Ostensibly, the hunting party ate and brought back game. This would make the Persians of the Achaemenian era (c. 700-330 BCE) occasional meat-eaters. But their fall back meal was always the bread and cresses they carried with them. We are given the impression that the bread the Persians ate was flat bread or bread cakes, and that the bread was made from both wheat and barley flour.
The ethic of moderation and modesty that marked the reign of Cyrus would regrettably give way to gluttony and opulence in the reigns of later Achaemenian kings.