Question for biology nerds

Hypothetically speaking, if somebody was only allowed to eat 1 type of food for the rest of their life and only drink water, what could they eat and not die?

Dishes like soup and stuff don't count, it has to be only 1 thing, like only chicken or only cucumber and stuff like that. My best guess would probably be some kind of plant, because I know there's stuff in those that we cannot produce but need, meanwhile all the stuff in animal meat is probably naturally producible. I really don't know much about biology tho, so really curious to see different answers.

I also wasn't fully sure which category this belongs to... It feels spiritually general discussions, but I figured it's TECHNICALLY about nutrition, so... yeah

I feel like if you were only to eat only one food for the rest of your life literally, you would never have all the nutrients and vitamins the body needs, since there's no possible food that has EVERY nutrient. You would have nutrition deficiencies and depending how long you eat it, your organs will slowly start to fail, and you would have other concerning side effects too. Which is why eating a diverse amount of food is important. 

It's an interesting question because I see videos saying "what food would you eat for the rest of your life?" and sometimes I just wonder how long I would survive eating a specific food.