Saw a cure in a sci-fi book I'm reading

Just a quick story:

So this morning before work I was working my way through "The Forever War" and the main character's sleeping partner is injured in a battle and her guts are damaged pretty badly. Almost as an aside he mentions that her complete gut flora was replaced with a "commercially available product." She couldn't see anyone for a few weeks after because it's a pretty big deal to replace the gut flora completely and also "embarrassing."

I read about 15 more pages but didn't comprehend a word about it because I was thinking about her new flora. What a lucky gal.

This book was published in 1974.

Okay, you want to know what attracted me to this topic - the sci-fi book mention!

Being the sci-fi nerd that I am. I will have to read that book now. Wondered if maybe you were referring to The Fifth Wave perhaps. And I was trying to jog my memory if a character had severe GI issues. lol

But we can dream can't we that in the future GI issues and the like will be a thing of the past or a mild ailment that is easily treatable.