The ketogenic diet in your link is cooked, and therefore not sustainable as it causes certain deficiency disease in time.
I tried the veggy oils, still had cravings so use unsalted butter for lack of better saturated animal fat. There's not enough denatured proteins in the butter to make trouble for me. This is Canadian butter, I read that it's different elsewhere.
Nausea means that you've eaten too much fat, so it's self-limiting.
Those who use the paleolithic model experience lethargy for at least 3 weeks; never heard of nausea.