Not wanting to blast an entire profession, and I am not even the guy you are talking with...
But to me, PhD in nutrition doesn't mean much, it is like PhD in underwater basket weaving, I am yet to met a single nutrition professional that could help me, and believe me, I looked really, really hard.
In the end the only people that could help me, were endocrionologists, biologists, and other scientists in fields that are not directly relation to nutrition.
And the reason for that, is precisely because of that high-carb recommendation, that is just insane, many cultures on earth lived just fine with low, or even zero carbs (extreme example: north-pole inhabitants, that in some places have diets that are 100% meat, organs included, since "regular" meat lacks some nutrients, like Vitamin C).
In more tribal places (all over the world too, Africa, Asia, Americas...) hunter tribes also tend to be healthier than farmer tribes (but also tend to have much lower population numbers).
And in many places, before FDA push for the vegetable agenda (I am not talking about veganism or vegatarianism, but about FDA constantly defending vegetable based food, including by accepting research that was fraudulent), people would happily eat lots of animal fats and meat, and live just fine. (example: in my country before the 60s, everyone used pork fat to fry stuff, and even make soap, but after vegetable oils became popular, and the government started to give strong subsidies to wheat, obesity, diabetes, etc... exploded, many common people still believe egg and cheese is absolutely evil, and prefer to stuff their faces with artificial sweeteners, soy milk, and salad with enough oily dressing to lubricate a car, than eat some eggs).