My real point in mentioning Phinney’s work was to illustrate that the advice has to be different for different people. When I first went keto/LCHF, it was with Phinney’s 100-125 g/day recommendation in mind, and it worked for me. There are people who can get into ketosis eating that much carbohydrate, and I appear to be one of them.
On the other hand, there are people whose metabolisms are sufficiently disordered that they need to adhere to a much lower maximum, and the 20 g/day recommendation is predicated on the Dudes’ experience.
Likewise, Phinney’s more recent experience with the general diabetic population has caused him to lower his recommendation to 50 g/day for their sake, and I’m sure the Virta coaches don’t hesitate to tell patients to eat less than that when it is warranted.
To further complicate the issue, there is also the matter of addiction to sugar and carbohydrate. As an addict myself, I find it much more helpful to adhere to the 20 g/day limit recommended by the Dudes and Carrie, since it is much less likely that I will get triggered to go on a binge when eating that little carbohydrate.
(Lest you doubt that sugar addiction is real, we celebrated my boss’s birthday a couple of weeks ago, and I am still feeling the effects of eating that piece of birthday cake and some of the other carbohydrate the ladies put out at coffee hour. I knew it wasn’t going to taste as great as I wanted and that I would regret it, and it didn’t and I do, but I am still dealing with the consequences. And it is only by God’s good grace—I mean that very literally—that I did not then leave the church and head straight for the Dunkin Donuts six miles down the road.)
I guess the lesson from all this is that a ketogenic diet is whatever keeps someone’s insulin low enough to allow nutritional ketosis, and that we never should have put the nation on a “heart-healthy” diet. The consequences of which have been horrific.