For 1 week at the start and at the end he eats no sugar or carbohydrate.

For 1 week he the middle he drinks water and takes magnesium.

That's it.

it was just a one time experiment as he wanted to do a 7-days water only fast and decided it would be better/easier to do a 7-days keto diet the week after and the week before. It's not something he does continuously all year long.