Minimum daily carbohydrate requirement: the misconception about glucose

I was flipping through a back issue of Mother Earth News this morning when I came across this common misconception in a reader's letter on the subject of stevia:

The brain needs glucose to function. The result of eating something that tastes sweet but doesn’t offer the energy source? You end up eating more calories later to fill up on what you told your brain you were getting in the first place.

Even though I do believe there might be some truth to the idea that artificial sweeteners can lead to overeating, it is categorically not true that we need to eat glucose-containing foods in order to keep the brain functioning, as is strongly implied above.

The carbohydrates we consume don't go directly to the brain.  Even a teaspoon of glucose doesn't make it there in a direct pathway.

What happens instead is an indirect process.  Dietary glucose is converted to glycogen and stored in the liver.  From there it is converted back to glucose so it can be used by the brain and tissues when it is needed via a metabolic process named glycogenolysis.  But that's not the only way to do it. 

Gluconeogenesis is the process by which animals and even plants, fungi, bacteria and microorganisms generate glucose from non-carbohydrates such as lactate, glycerol, and amino acids.  In other words, fats and proteins can be used instead.

So while it is absolutely true that the brain requires glucose to survive, it is not at all true that we need to consume it in that form.

Whatever the original source of the glucose, it doesn't ever make it directly to the brain.

The body uses  a multi-step process that allows it to finely regulate the amount that flows to the brain and tissues, and to store excess energy for times when it may be needed.

This is why is is possible to live perfectly well on a diet of fats, proteins and non-starchy vegetables.  It might not be as interesting or affordable as you would like it to be, but there is nothing wrong with it.  And there are plenty of people who believe it is much healthier than a diet that does include carbohydrate.

The bottom line which seems to be so poorly understood:  there is no minimum daily carbohydrate requirement.