This is a really interesting point, and something I've pondered before. Bacterial die off can be particularly bad because Lipopolysaccharide (LPS), a form of endotoxin, is released from the membranes of the dead bacteria and can potentially find its way into the bloodstream if the tight junctions in the gut are compromised (ie: intestinal permeability / leaky gut). LPS is implicated in many (maybe most) autoimmune conditions, heart disease, non alcoholic liver disease, and a host of other conditions. If a constantly changing diet is causing regular shifts in the microbiome, this would cause regular bacterial dieoff events, and potentially regularly elevated LPS in the bloodstream.

It would seem logical that the ideal situation in the gut is a diverse and stable microbiome. Which makes sense if you use ecology as a comparison, where something like an apex forest is both stable and diverse. And this is made possible because it has a very slow changing set of energy inputs. If the soil composition was constantly changing in a forest, there would be regular events of trees dying off and getting replaced with less mature species, resulting in both less stability and diversity. The land would also be likely to get overtaken by invasive species, as you can observe on patches of land that are routinely disturbed, like the side of a highway.

I can't find the link right now, but a fascination of mine has been all potato diets (the potato hack). One guy who did this (or maybe there was a study) tested his microbiome before and after, and the after test showed a much healthier balance of species and a greatly increased diversity. At the time I remember being surprised by the increased diversity, as I, like most people, assume greater diversity of food would result in a greater diversity of bacterial species. But I have to imagine that a general characteristic of diverse diets is that they're not very stable. If someone is eating 100 different foods, it's unlikely they eat all of those 100 every day, so there is a constantly changing input to the gut, which would make for a constantly changing bacterial colony, which in theory would result in reduced diversity and regular dieoff events.

This all makes a lot of sense too if you think about hunter gatherers and early agricultural peoples. They may have eaten a large number of plants and animals in the course of a year, but I imagine their diet would have rotated very slowly. So maybe they're foraging or growing a few things one month and that comprises the majority of their diet for a month or two. Then new things come into season and the diet shifts, and the microbiome shifts with it. This is much more stable than us modern humans that eat Thai food on monday, burgers on Tuesday, Mexican on Wednesday, and then Salad on Thursday when we're feeling bad about our food choices. It's only in the modern age with long distance shipping and refrigeration that we've had the luxury of changing our diets on the daily. Is this abundance of choice killing our guts?

I think I'm going to experiment with a simple diet to see if it can fix my gut issues (IBS, maybe SIBO). An all potato diet seems too boring, but I think I can handle potato, steak, and broccoli, which sounds pretty similar to a bodybuilder's diet. A ratio of 6:2:1 by weight (potato:broccoli:steak) meets all nutritional requirements, other than coming in a tad low in calcium. Daily intake of 60oz potatoes, 20oz broccoli, 10oz sirloin steak, and 1/2 tsp calcium carbonate satisfies all dietary requirements and clocks in at 2200 calories.