[codeulike]

The NHS prescribe the ketogenic diet for some forms of epilepsy. That is, the UKs national health service prescribes keto as a treatment. And so the answer to the question posed by the OP "Can an extreme low carb diet be used as medicine?" is clearly Yes.

You get a diet plan, support, specialist foods and ingredients, ketone testing kits, etc, all on prescription.

There has been proper research into Keto as a treatment for some forms of epilepsy, and in some cases it performs as well as the best AEDs. See https://pubmed.ncbi.nlm.nih.gov/25524846/ and https://pubmed.ncbi.nlm.nih.gov/16146451/