Who has been 100% carnivore (or close enough) for long periods of time (ie 12 months plus)?
There are a few people like Charlene and Joe Anderson, Kelly Williams Hogan, and Charles Washington who have been doing it for a decade or more. There's also the célébrités du jour, Shawn Baker and Mikhaila Peterson who have been doing it for well over a year.
I think a lot of people end up using it as an elimination diet, and then adding things back in as tolerated. Like I said before, with the exception of some people (like Mikhaila Peterson, for example), I think there are a variety of healthy ways to eat. That being said, I do think the carnivore diet is a good starting point.
My concern relative to this one is for the health of the gut microbiome.
I think we have to careful when we apply new sciences. We're just starting to understand the microbiome, and at this point the only mainstream microbiome therapy we have is to kill it all off and re-seed with donor poop. We don't know
how to reliably change it without using a scorched earth approach, and even if we did, we don't know what bugs do what. Think of the genome project. We now know exactly what gene causes cystic fibrosis, and that still hasn't changed CF treatment because we're not sure how to change the gene (although they are working on that). We don't know exactly what bugs cause inflammation, obesity, and mood problems, or which ones decrease inflammation, aid metabolism, and help our gut produce loads of serotonin. We also don't know specifically what foods each type of bug likes.
I think microbiome therapy is going to be a big part of medicine in the future, but we just don't have it figured out yet. From what few people I've seen who have had their microbiome tested after a few months of carnivory, it seems like it does alright. The microbime changes in response to what it's fed (which is going to happen any time someone changes their diet), but from what I've seen, people have had a lot of "good" bugs, not many "bad" bugs, and a pretty high variety overall. Obviously, all the people who got back negative results might have just kept their mouths shut...
In areas where basic science is lacking, we have to turn to other areas to fill in the gaps. In this case, I look at anthropology. We look at cultures that have had meat-only diets for large parts of the year, and we don't see any evidence of rampant gut dysbiosis. We can also look back to (in our specific case,
@Anna C ) our European ancestors from a couple hundred thousand years ago, who wouldn't have had access to plants for months or years at a time. They died of a lot of things (accidents, infection, and all the infant mortality causes that we take for granted today), but there was literally hundred of thousands of years for our gut microbiome to adapt to long stretches of a low-residue diet.
I would agree that some people's microbiomes are going to be less able to adapt adequately, and I think this is one major cause of failure of the carnivore diet. Our microbiome depends on where we live and what we eat, and if those things change, so does out microbiome. If, for some reason that we have yet to understand, our microbiome is unable to adapt properly, problems ensue. If someone starts a new diet with one of the "wrong" microbiomes (one that can't adapt to that diet), they'll likely have issues. I think this explains part of the phenomenon we see of someone trying a diet, having a terrible time, doing a different diet instead, and then trying the original diet again a year later and succeeding. Their microbiome (and likely metabolism), has had time to "come around" to a place where it can now adapt. This is one of the reasons why it pains me to see such religious zeal surrounding diet; it pushes people to force themselves through months of brutal "adaptation," when they could likely get the desired results with a slightly different approach.