For anyone looking for a good reference for the minimum amount of carbs required for life, there’s a Dietary Reference Intake published by National Academies Press that serves as the source for the recommendation of 130g of carbs daily.
BUT…it also acknowledges that the entirety of the body’s glucose needs can be provided for by gluconeogenesis, provided adequate fat and/or protein as substrate.
Here’s where you can get the PDF, for free: http://nap.edu/10490
The relevant portion starts on page 275, which contains specifics on (their words) “Clinical Effects of Inadequate Intake” including the following:
“The lower limit of dietary carbohydrate compatible with life apparently is zero, provided that adequate amounts of protein and fat are consumed. However, the amount of dietary carbohydrate that provides for optimal health in humans is unknown. There are traditional populations that ingested a high fat, high protein diet containing only a minimal amount of carbohydrate for extended periods of time (Masai), and in some cases for a lifetime after infancy (Alaska and Greenland Natives,Inuits, and Pampas indigenous people) (Du Bois, 1928; Heinbecker, 1928). There was no apparent effect on health or longevity. Caucasians eating an essentially carbohydrate-free diet, resembling that of Greenland natives,for a year tolerated the diet quite well (Du Bois, 1928). However, a detailed modern comparison with populations ingesting the majority of food energy as carbohydrate has never been done.”
as well as:
"Azar and Bloom (1963) also reported that nitrogen balance in adults ingesting a carbohydrate-free diet required the ingestion of 100 to 150 g of protein daily. This, plus the glycerol obtained from triacylglycerol in the diet, presumably supplied adequate substrate for gluconeogenesis and thus provided at least a minimal amount of completely oxidizable glucose.
The ability of humans to starve for weeks after endogenous glycogen supplies are essentially exhausted is also indicative of the ability of humans to survive without an exogenous supply of glucose or monosaccharides convertible to glucose in the liver (fructose and galactose). However, adaptation to a fat and protein fuel requires considerable metabolic adjustments."
They go on to do some fear-mongering about what other effects “may” occur with “inadequate” intake of carbs, but that appears speculative at best.
Worth keeping handy for times when someone asks to see the science on your contention that we do not need to eat carbs to fuel the brain (or the rest of our bodies).