High fat very very low carbs. Its a challenge diet-wise. Without carbs the body shifts to making ketones for energy and much less glucose.
You don't really even need high fat diet, if you practice daily intermittent fasting...basically eat during only a 6 hr period of the day (while definitely avoiding carbs, preferring protein) and fast for 18 hrs.
It’s hard on the kidneys and could lead to kidney failure. Should guzzle large amounts of water while on this diet.