Based on my visit to India, travels around middle east, and third world countries. Oils, and fats are the most affordable way to get a high enough amount of calories in a diet for the poor masses. So even if you're poor, and eating rice everyday. It will be typically with something oily and some spices to add flavour.

I read the book, he travelled to multiple continents and generally this is pre- industrial diets, or prior to introduction of vegetable and seed oils, refined sugars, processed carbs, etc. Because he was able to do this research in the 20s, the industrial diet hadn't quite taken over. He also studied mummies in South America. They overwhelmingly had perfect teeth, prior to introduction of modern junk food.

I wonder how they survived berries. Because berries are not good for your teeth due to high (natural) sugar content.

Modern fruits have wayyy more sugar than wild plants, due to years and years of selective breeding.

Even then you still have a lot of fiber and acid to slow down the release and absorption of sugars.

Also berries are fairly seasonal AFAIK

Price observed the traditional cultures he had access to at the time, you can read the details for yourself here: http://www.journeytoforever.org/farm_library/price/pricetoc....