Do you have any links for that info John?
I’d be really interested to read the stuff on carbs.
Protein, I would agree with (having been carnivore now for nearly 15 months). Not sure about the fat, since protein is essential. But that is a sort lifespan on just carbs (since many carbs come with protein attached), so v curious to see how they tested it...
As for the OP’s question:
Someone with the capacity to produce insulin will do so, all day, every day, whether they eat carbs or not, since insulin has multiple functions.
The body may be able to manage without dietary carbs, but very small amounts of glucose are still needed. This can be produced by breaking down other foods to create glucose.
These are the functions of insulin in the human body
http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/pancreas/insulin_phys.html
And they are much more extensive (including fat, protein and potassium metabolism) than just pushing glucose into cells.