Holistically: https://pmc.ncbi.nlm.nih.gov/articles/PMC5563491/#S1
More pointedly:
> Five healthy rhesus monkeys, three male and two female, weighing from 2.4 to 6.1 kilos, were fasted for periods of 2 to 4 days... With one exception, the monkeys developed a ketosis within 2 days
https://www.sciencedirect.com/science/article/pii/S002192581...
Note that Attia's article is about rhesus monkeys.
Holistically: https://pmc.ncbi.nlm.nih.gov/articles/PMC5563491/#S1
More pointedly:
> Five healthy rhesus monkeys, three male and two female, weighing from 2.4 to 6.1 kilos, were fasted for periods of 2 to 4 days... With one exception, the monkeys developed a ketosis within 2 days
https://www.sciencedirect.com/science/article/pii/S002192581...
Note that Attia's article is about rhesus monkeys.