With necessary food gone, I expect most cheap foods just meant for nutrition would disappear. But many people still eat for pleasure. How does this impact the food industry? What (if any) foods or types of companies remain?
People don't need tobacco or alcohol or recreational drugs to survive, but they still consume them... for pleasure. Even at the expense of their health. In fact, western people already eat more than they need just to merely survive, and that doesn't impact the food industry per se.
Hedonism and consumerism will drive the food industry. The maximum that can happen is: since the poor won't need food, food might become a luxury.
A Generational Cultural Shift
In developed nations, while older generations are still drawn to the pleasures of food which they had grown up with, the younger generations begin to forego its consumption. They are moved by the environmental benefit of abandoning food consumption, as well as the time and financial savings.
With food no longer being of concern numerous sources of conflict and tension would ease. People have far less to worry about, if I have no money then shelter is the only thing of concern. It is easier to shelter then it is to feed people.
With famine gone, once frail bodies are beginning to grow strong once more to focus now on improving shelter and infrastructure.
I think this would manifest in a rapid gains in developing nations, specifically in regard to the last two points.
You would see a decline in the "fast food - fast satiating"-sector in some areas of the world. So maybe less McBonald or BurgerMink places, but the ones who would stay would change to a somewhat restaurant-style type. I assume that eating food would not result in getting fat, so people would stay longer in such places, eating for pleasure. The portions would get smaller, but you could eat a whole menu in one sitting.
The production lines would shift from quantity to quality. As smaller portions are needed the crops don't have to be so big and can be tended more.
What would be interesting is: What happens to Africa or the Amazonian Forest? You see, they would not need to fight for territory to grow bananas or make pastures anymore. There would be no need to have so much palm oil.
So, as Joe Kissling, noted: The food industry tells no one. And they have more money than the whole big pharma industry.
Perhaps some farmers, if paid by the government could plant and maintain trees and other vegetation that will clean our air. Or they may be able to manage the land as a park. Already in the northwest many apple farms have been converted to vineyards. As to the large scale processing (food corporations), packaging, and distribution industry (truckers) may find themselve out of a job. There will be no need for all the migrants. Will the population experience growth? Will the farmland be turned into homesites?
Food would become more of a luxury and become more expensive because people who are financially challenged won't have a need for food and only people with extra money would eat food. In other words, high-end restaurants would remain but things like fast food and family restaurants would be gone. Grocery stores would be very rare because only people with money and time would be able to use cooking as a hobby. So the food industry might be about on the same level as the miniature modeling industry.
Food will shift from being a necessity to being a luxury item.
Food is now Entertainment
However it's not going to be something that is limited to the wealthy. The very poor might forgo it as an unnecessary expense, but the vast majority will view it much like they view entertainment. Not necessary, but something you might want to do on a regular basis, like going to the movies, listening to music, watching sports, playing video games, etc. Eating with your friends and enjoying tasty food will still be something people do, but they will probably eat fewer meals and more snack or dessert type foods like ice cream or cake.
In terms of farming, staple crops like rice, wheat, potatoes etc. are likely to drastically decrease in production and farmers who grow these will likely take a heavy blow as a result. Other crops like sugarcane may see an increase as land is freed up. There will also likely be a decrease in livestock, but by how much I can't even begin to guess.
The food industry itself is likely to shrink as the lowest quality, highest capacity production will no longer be necessary and will shrink according to demand. But I imagine that the parts that tout itself as more entertainment (like the food network) will remain relatively unaffected. Food will still be a relatively cheap commodity (in the short term, it will likely be even cheaper than normal) much like electronics, since there is already massive expertise in the area of food preparation and food production. Fast food restaurants are likely to decrease in quantity as demand decreases, and they shift more toward quality, but people are probably going to still go and enjoy them much as they did before since it's cheap and tasty. Heck they may maintain popularity just because poor nutritional value of fast food is no longer a concern.
In the short term, there is going to be some upheaval for people who work directly in the farming and food industries. For well developed countries that have tiny portions of GDP that come from agriculture, not much will change besides a lot of lost jobs. It will amount to a very large company laying off a large portion of its workforce. Lots of lost jobs and a decrease in prices as everyone scales down and surplus is high, but eventually everything will stabilize. For poorer, undeveloped countries this could range anywhere from civil unrest to an economic depression to destroy them and throw them into a state of civil war. It's really a toss up depending on local conditions.
There is no doubt in my mind that farming and food industry will decrease in size. But since people can still enjoy it, it will likely go the way of entertainment and become just another activity for people to do.