As long as we're sharing anecdotes; about 10 years ago I quit being vegan and transitioned into a carnivore diet. I now eat mostly red meats and my gut has never worked better. When I was vegan I had constant GI issues to the to the point of hospitalization.

Everyone is different.

Just to finish off this Goldilocks story: I've been vegan for four years, and previously ate a meat and dairy heavy diet. I noticed basically no change to my gut health--it has been pretty good, with occasional minor issues, for my whole life.

This is the one for me. Keto, Vegan, Whatever specialty diet I try results in elevated energy and mood for a week or so and then a return to baseline. (Except with keto where I usually have no energy after a few weeks).

Anecdotally, I'm far healthier and more energetic than I was before starting keto a decade ago. I recommend everyone to give it a serious look.

Granted, I can't entirely separate the effects of ketosis in and of itself from an overall cleaner diet with more vegetables and fewer processed foods. It's possible that the same diet with butter swapped out for quinoa would have yielded a similar result.

As far as sweeteners, my go-to is liquid stevia, which I use about 1/5 a cup of daily. When I need a solid sweetener (e.g. for baking), I use inulin fiber sweetened with stevia and monk fruit, which creates a nicer texture than actual sugar IMO. I also have allulose on hand for specific use cases (e.g. caramelizing), but I can't really stomach it in large quantities.

My annecdata is that I spent two years eating a healthy vegetarian diet (to contrast with french fry vegetarians) and my digestive tract never adapted. I switched back to eating plenty of lean meat (mostly chicken and fish) and the plumbing almost instantly began working properly.

The added benefit is that my diet is much higher in protein and lower in carbs, which definitely has helped me build and maintain muscle and reduce dad bod.

Again, just annecdata, but maybe individuals have differing nutritional profiles that work best for them?

Or maybe the masses inside those individuals have different needs? Different bacteria levels responding differently to various diets. I think that's what some of the microbiome companies were working on, but I don't think it was ever successful.

You can run the same experiment with water fasting. We overeat.

From my experience, the worst thing is eating the same thing all the time, no matter what it is.

The goal is to keep your microbiota as far as possible to a monoculture.

I am absolutely not an expert on this subject, but so far, my understanding is that there are not really "healthy" bacteria, there are only healthy mixes where different species balances and keep the other from growing.