system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the reason that it is common to eat 3 meals in a day?
gpt
'Mealtimes' are constructed to accommodate social, geographic and economic norms and lifestyles. Doctors will often ask you if you're getting three square meals, but that's just because its an easy way of gauging whether you eat enough. Its not the natural, or even optimal, way of doing things. Naturally, the time we eat should be determined by our stomachs, not the position of the sun in the sky. That's why more recently doctors recommend you have healthy snacks throughout the day.  


In modern Western culture, we eat three square meals because it coincided with industrial work patterns. 


The industrial revolution brought a very strictly regimented workday. Suddenly people were very concerned with hours and minutes. You couldn't simply allow workers on a factory line to pop off whenever they liked because they were hungry. Over time, our eating patterns developed around that industrial workday, to the point where they became a social and cultural fixture. You had breakfast before work, you had lunch with your peers when the line shut down at midday, and then you would usually have dinner with your family after the workday. We developed social patterns and rituals around those ideas, until they became so entrenched that many of us thought that's just how people have always eaten. 


In the modern world, with ready-to-eat meals available at all hours, those strict lines are also diminishing. You don't go home and have a big family dinner as much anymore. Lunchtime is also not necessarily a shared meal for all workers in a given workplace, because the nature of the workplace has changed.


In short, its the way we organize our society that really determines our mealtimes. When we work, how we work, and even things like gender roles or technology can determine the cultural norms for mealtimes.