, in city builders like Cities: Skylines people eating is at a very abstract level. You can assume that people must be eating, but you have no idea what or when. As "mayor" you build services such as fire departments or schools, but you don't ever get down to the eating, sleeping, sex level.
Cities: Skylines works basically like Sim City: You zone for "residential," "commercial," or "industrial" and the game decides what actually to build. What Cities: Skylines adds is an "Offices" zone and the ability to create districts. You can make a district specialize in certain industries: Agriculture, Minerals, Timber or Oil. Within an agricultural district you have no control over which industries get built. There are already grain and vegetable farms and orchards in the game, but there are also animals. The game picks what to build, so even if you made 100 vegan mods, the game could build a chicken ranch and mess you up. If you designate no districts as agricultural, then no farms or food processors get built, so no ranches. In your commercial zones you might well get a grocery store or two, but you never see what they actually sell. So, you could build a city where no meat is produced, but as to whether every one of your denizens is vegan would have to be in your own imagination since import/export is part of the game. If you don't want to drill for oil or mine minerals you don't have to.
It is pretty easy to provide all renewable power: hydro, wind and solar can supply all of your electrical needs. In fact, in the beginning all you can afford is a windmill generator. You soon have to build another and another, but more sophisticated windmills and solar come along as your city grows. The biggest ecological problem is garbage. In the beginning all you can afford is a landfill and then incinerators, so garbage-related pollution is always a problem. Recycling eventually makes a percentage cut in garbage, but never fully. Also in the beginning you are pumping out raw sewage (Keep your intake up-stream from your outflow!) and even after you can build water treatment plants they pollute. The game tracks air pollution (which is mostly from industry) and noise pollution, but these are more abstract. You can plant trees, but that is not terribly effective.
Hope this helps. You might check out SC4 and the whole range of agricultural mods available for that. SC4 is available at GOG and the best mods are at Simtropolis, SC4 Devotion and Sim Peg (lots of farming options).