The sixth of the eight Precepts and ten Precepts is Vikala bhojana vermani sikkhapadam samadhiami, I take the precept not to eat at the wrong time. 'Wrong time' (vikala) has long been interpreted to mean after noon or midday, although I know of no place in the suttas where this is specifically stated. The overall purpose of this rule is clear enough – to encourage moderation in eating (Sn.707) and to keep drowsiness due to a full stomach at bay. But the part about not eating after midday is less clear. The origin story in the Vinaya explaining this rule is unconvincing and obviously a later invention. According to this story, a monk was standing at someone's door late at night. As the woman of the house approached the door a sudden flash of lightening illuminated him, frightening the woman half to death, and to prevent this from happening again the Buddha instituted the rule. The only justification the Buddha gives for this rule is that it is good for the health and he does not mention what the 'wrong time' is other than to say the 'evening' or 'night' (ratti). He said, 'I do not eat in the evening and thus I am free from illness and affliction and enjoy health, strength and ease' (M.I,473). But I can see not reason why eating only in the morning should be any more or less healthy than eating only in the afternoon.
I suspect that the rule has its origins in two things. That eating before noon was already a well-established convention amongst wandering ascetics and the Buddha simply asked his monks and nuns to follow this convention. And the reason why this convention evolved in the first place was probably because, then as now, Indian peasant women cooked all the day's food early in the morning and the main meal of the day was in the morning. In other words, the most convenient time to go for alms gathering (pindapata) was in the morning. Noon was probably used as the cut-off point for not eating because it could be known exactly. Its also pretty certain also that monks and nuns only eat one meal a day because, not doing hard physical labour, they did not need that much food. So it is important to understand that noon is not some magical time, after which consuming food becomes a moral failing. It is just a convenient, and at that time a practical, way of dividing the day.
I suspect that the rule has its origins in two things. That eating before noon was already a well-established convention amongst wandering ascetics and the Buddha simply asked his monks and nuns to follow this convention. And the reason why this convention evolved in the first place was probably because, then as now, Indian peasant women cooked all the day's food early in the morning and the main meal of the day was in the morning. In other words, the most convenient time to go for alms gathering (pindapata) was in the morning. Noon was probably used as the cut-off point for not eating because it could be known exactly. Its also pretty certain also that monks and nuns only eat one meal a day because, not doing hard physical labour, they did not need that much food. So it is important to understand that noon is not some magical time, after which consuming food becomes a moral failing. It is just a convenient, and at that time a practical, way of dividing the day.