As a scientist I invent a bacteria that can live in the human gut and process cellulose for us. Yay! No more world hunger as everyone can eat grass and get glucose from it. I spray it all over the world so eventually everyone will have this bacteria in their system.
It isn’t just the bacteria you need, but an entire new anatomy. If you want to get sufficient nutrition from grass, you would have to eat enormous amounts of it and keep it in your stomach for a long time as it ferments. You would spend a lot more of your time eating and chewing. It would, however, fit in with the modern sedentary lifestyle.
Toilets would need to be redesigned to allow for greatly increased capacity. Presuming the same flush mechanism was used, demand for water would go up dramatically.
I’ve read a scifi novel or a short story with this theme ages ago. Sadly I can’t remember the name, but I do remember the main result being hungry Africans eating everything and turning the whole continent into a desert.
The job market for dentists would explode if you are imagining people actually consuming grass. Even cooked, grass is tough and abrasive and will require a lot of chewing. Human teeth would wear out fairly early in life on such a diet. Better to finely mill the cellulose material and mix it in with other foodstuffs as an extender.
Not to mention that lots of plants are distasteful or toxic and the ability to digest cellulose won’t change that.
There are a metric shitton of scientific discoveries that never go anywhere, but people are already working on this (although their work on breaking up and rebuilding cellulose is done in a lab and not in a person’s stomach).
No idea what the unintended consequence would be. A bushel of corn can support a person for about 2 months and costs about $4.
What was the name of ancient Greek philosopher who speculated about the possibility of people not needing food but being able to satisfy their hunger by looking at food and rubbing their stomach?
The chem trail nuts would finally be able to say “See, I told you so”. You would pave the road for all the other conspiracy theorists to get louder and nuttier.