[js2]

Glucose is the only nutrient that neurons are using in normal conditions.

And to elaborate, the other is ketone bodies produced by the liver from fatty acids.

Their production occurs in healthy individuals as nutritional ketosis under a carbohydrate restricted diet (typically less than 100g/day) or in diabetics as the pathological condition ketoacidosis.

[stefantalpalaru]

Not ketone bodies, but lactate. More details in this article titled: Energy Substrates for Neurons During Neural Activity: A Critical Review of the Astrocyte-Neuron Lactate Shuttle Hypothesis[1]:

> The brain can consume lactate as a substrate, as has been demonstrated by studies showing that the brain uses lactate during hypoglycemia or during periods of elevated blood lactate [...]

> However, because lactate does not pass through the blood-brain barrier nearly as well as glucose [...], lactate cannot serve the brain as a blood-borne substrate the way glucose does.

[1]: http://www.nature.com/jcbfm/journal/v23/n11/full/9591474a.ht...

[rdmcfee]

Many people experience some ketone body production and metabolism well eating SAD (standard American diet). Fasting overnight and skipping breakfast, or having a long workout more than 4-5 hours after your last meal will cause this.

Nutritional ketosis, unlike ketoacidosis is a loosely defined term. Everyone has experienced it on some level. Perhaps just not at extreme levels like people pursing NK with vigour.