CAC tests come with a non-trivial radiation exposure if someone is getting them every few years.

The other problem is that they’re picking and choosing which tests to believe and which to ignore.

They disregard their cholesterol tests because they don’t like the results, but embrace one or two CAC tests because they do like the results (when they’re young).

However the CAC results are a lagging indicator of cumulative damage that has been done. Cholesterol tests are correlated with the rate of damage occurring.

So embracing CAC and using it to justify ignoring LDL and others is the problem.

I think the unknown factor here is whether other benefits of keto over a standard American diet--possibly including reduced inflammation, BP, blood glucose, and body weight--balance out the effect of cholesterol. CAC measures actual damage already done, while cholesterol is just one of many factors.

The downside, of course, is that once the damage is done, it's done, so it's a risk. (And as you said, they won't see the damage in their 20s.)