Here’s a study that is better formulated than most.
Study is 24 weeks long ( about 6 months), long enough to conclude if it works or not, but I don’t think long enough to claim to study long-term effects.
Why they upped the carbs from 20-30 to 40-50 grams at 12 weeks is questionable, but the participants still got positive results.
This study might be good to show a doctor or skeptic to show effectiveness of a ketogenic diet.