Ethnographic Data of Modern Hunter Gatherers

Abstract:  In the past, attempts have been made to estimate the carbohydrate contents of preagricultural human diets. Those estimations have primarily been based on interpretations of ethnographic data of modern hunter-gatherers. In this study, it was hypothesized that diets of modern hunter-gatherers vary in their carbohydrate content depending on ecoenvironments. Thus, using data of plant-to-animal subsistence ratios, we calculated the carbohydrate intake (percentage of the total energy) in 229 hunter-gatherer diets throughout the world and determined how differences in ecological environments altered carbohydrate intake. We found a wide range of carbohydrate intake (≈3%-50% of the total energy intake; median and mode, 16%-22% of the total energy). Hunter-gatherer diets were characterized by an identical carbohydrate intake (30%-35% of the total energy) over a wide range of latitude intervals (11°-40° north or south of the equator). However, with increasing latitude intervals from 41° to greater than 60°, carbohydrate intake decreased markedly from approximately equal to 20% to 9% or less of the total energy. Hunter-gatherers living in desert and tropical grasslands consumed the most carbohydrates (≈29%-34% of the total energy). Diets of hunter-gatherers living in northern areas (tundra and northern coniferous forest) contained a very low carbohydrate content (≤15% of the total energy). In conclusion, diets of hunter-gatherers showed substantial variation in their carbohydrate content. Independent of the local environment, however, the range of energy intake from carbohydrates in the diets of most hunter-gatherer societies was markedly different (lower) from the amounts currently recommended for healthy humans.

Abbreviations: P:A energy subsistence ratios, plant-to-animal energy subsistence ratios

http://www.sciencedirect.com/science/article/pii/S0271531711000911

Interesting research!  Very interesting that the 30% number is so close to Barry Sears' speculation in The Zone Diet.  While The Zone Diet is inarguably effective, it is also tedious, and I think there are many, in particular those who are "recovering" from being significantly overweight, who benefit from a much lower dose of carbohydrate - less than 100g/day. 
The takeaway - healthy humans can thrive on a variety of macronutrient ratios, but there are many who will suffer when eating large quantities of carbohydrates at "agriculturally availability" for 12 months per year - never mind the impact of abnormally high intake of fructose, low sunlight exposure and therefore low vitamin D levels, excess omega 6 fatty acids from their "oil fed plants", low levels of vitamin K2, and "light contaminated sleep".