For every single person in a city you need 2 lbs of grains a day.
You can go to the historical record, you can research in China, in India, in the Near East, and you will still be talking about 2 lbs of grain-based food for every person in the city every day.
Always the largest customer:
All cities require fuel: oil, gas, electricity, and so on. What I want to talk about today is the energy that fuels the people in the cities—food. Without food energy, a city is nothing. A city is nothing without the people who work and play and enjoy or suffer through the city, and they require food.
What do cities need in terms of food?
There’s only one way to feed a city, at least historically, and that’s to feed it with grains—rice, wheat, maize, barley, sorghum, etc.. You can go round the world, and there just aren’t cities that aren’t fed on grains, except for possibly in the high Andes.
Basically, to maintain a city, you’ve got to get grains into it. Be it Bangkok, be it Guangzhou, be it London, or be it Rome—throughout history, grains and cities are two sides of the coin.
And what do you need in terms of grains? For most of history—really, until about 150 years ago—most people in most cities, except for the very wealthy, lived almost exclusively on grains. They got about ninety percent of their calories from grains.