It's kind of like how most religions have some insane stuff in their holy texts, but regular nice people turn it in to a positive reminder to be kind by filtering it with their human inexactness.
This debunks that long term low-carb is unhealthy.
[1] https://www150.statcan.gc.ca/n1/pub/82-003-x/2008001/article...
https://thepaleodiet.com/north-american-plains-indians-tall-...
So in general it's very hard to get good data on life expectancy on these fringe groups.
Then there's a question of how much access to health care should be needed? I was recently reading about a study that found when western diets entered a region health care costs go up. I was reading about it in Barons which is a financial publication. I imagine they are looking for investment opportunities. But, the observation is interesting. I'd link it if I could find it.
If you look at the US causes of death, a high percent of them are related to lifestyle. Like so many heart disease issues being linked to smoking or arterial blockages (and they've studied the causes of those). If a group doesn't have those lifestyle components they they have better health and longevity.
[1] This paper has images of atherosclerosis in the coronary arteries of a 45 year old Inuit woman who died 500 years ago - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC325106/pdf/thij...
[2] https://www.atherosclerosis-journal.com/article/S0021-9150(0...
Keto actually looks like it might be bad for long term use based on some studies. For someone who finds that it helps them lose weight, it will still be beneficial as long as they they continue to lose weight, but it probably isn't great as a long-term lifestyle change when not losing weight.