“Not even a question that should come up” is a pretty sour attitude to take in general, and I don’t even think you’re right.

Fiber does have a health impact as you say, and having good health is one of the main ways known to delay death. And what is survival but the delay of death?

My point is that by eating a larger variety of nutritious food, you are less likely to suffer from poor health due to a lack of something you need.

There are a long list of illnesses caused by vitamin deficiencies, including Scurvy, Rickets, magnesium deficiencies and iron deficiencies (as well as others). These can be life threatening too, so survival is very much a question that should come up.

> The only thing you're really missing there is dietary fiber

It misses iron, so it puts him at risk of anemia. Which is very real thing.

Scurvy and other vitamins deficience diseases are very real thing too.

So yes, if that food was literally all he eate long term, the question of survival makes perfect sense.

You sound like this was a certain thing, whereas nutritional science is very complex.