Evidence for Glucose #

Every substantive claim on the Glucose page is checked against current research. Here is each claim, how well today’s evidence supports it, and the sources. The full, de-duplicated source list lives on the references page.

Supported · strong evidence — The brain is roughly two percent of body weight but accounts for about twenty percent of the body’s energy use, with much of that spent on neuronal signalling.

That the human brain consumes roughly 20% of resting energy despite being ~2% of body mass, dominated by the cost of restoring ion gradients after signalling, is textbook neuroenergetics and remains uncontested in 2026.

Sources: Mergenthaler, P., Lindauer, U., Dienel, G. A., & Meisel, A. (2013), Sugar for the brain: the role of glucose in physiological and pathological brain function. Trends in Neurosciences — https://doi.org/10.1016/j.tins.2013.07.001 · full reference ›

Supported · strong evidence — Glucose is the brain’s main everyday fuel, oxidised by neurons to supply the energy they use to fire and maintain themselves.

Glucose as the obligatory primary fuel of the adult brain under normal conditions is well established; the page’s hedge that ketone bodies can substitute during fasting or ketosis is also correct and keeps the claim accurate.

Sources: Mergenthaler, P., et al. (2013), Sugar for the brain — https://doi.org/10.1016/j.tins.2013.07.001 · full reference ›

Supported · moderate evidence — The brain holds only a small fuel reserve (mostly glycogen in support cells) and depends on a steady supply of glucose from the bloodstream.

Brain glycogen is real but small relative to demand and is held chiefly in astrocytes rather than neurons, so the brain relies on continuous delivery; the page’s revised wording (a tiny store, not ’neurons cannot store glucose’) matches the current understanding better than the older absolute claim.

Sources: Mergenthaler, P., et al. (2013), Sugar for the brain — https://doi.org/10.1016/j.tins.2013.07.001 · full reference ›

Supported · moderate evidence — When blood glucose actually falls too low (hypoglycaemia), cognition suffers measurably — attention, reaction time and memory become slower and less reliable.

Acute hypoglycaemia reliably impairs attention, processing speed and memory in experimental and clinical studies; the page correctly frames this as a genuine shortfall (e.g. diabetes medication or prolonged fasting) rather than normal blood-sugar fluctuation.

Sources: Mergenthaler, P., et al. (2013), Sugar for the brain — https://doi.org/10.1016/j.tins.2013.07.001 · full reference ›

Supported · moderate evidence — The hippocampus is among the brain regions most sensitive to a shortage of glucose, so a depleted state is a poor one for forming new memories.

The hippocampus has high metabolic demand and is notably vulnerable to energy deprivation, and hippocampus-dependent memory is among the first functions to degrade under low glucose; the directional claim is well supported, though it is framed qualitatively rather than as a precise effect size.

Sources: Mergenthaler, P., et al. (2013), Sugar for the brain — https://doi.org/10.1016/j.tins.2013.07.001 · full reference ›

Supported · strong evidence — Dietary carbohydrate is the main source of the body’s glucose, with fibre-rich whole foods releasing glucose more gradually than refined sugars.

That blood glucose derives mainly from dietary carbohydrate and that fibre and food matrix slow its absorption (the basis of the glycaemic-index concept) is well-established nutritional physiology and uncontroversial in 2026.

Sources: Mergenthaler, P., et al. (2013), Sugar for the brain — https://doi.org/10.1016/j.tins.2013.07.001 · full reference ›

Supported · moderate evidence — For a healthy person, a normal balanced diet keeps the brain adequately fuelled; sugary ‘brain food’, glucose tablets and timed snacking are unnecessary.

Tight homeostatic regulation keeps blood glucose within a narrow range in healthy people, so deliberate carbohydrate ’topping up’ confers no reliable cognitive benefit; this corrects the earlier page’s overstated advice to load up on snacks before they feel hungry. Acute glucose-dose studies show, at best, small and inconsistent effects, mostly in fasted or older adults.

Sources: Mergenthaler, P., et al. (2013), Sugar for the brain — https://doi.org/10.1016/j.tins.2013.07.001 · full reference ›

Supported · moderate evidence — Eating refined sugar before studying does not boost brain performance, and a single sugary snack does not by itself cause type 2 diabetes, which develops over years from overall diet, weight and activity.

This deliberately walks back the original page’s claims that sugary snacks meaningfully impair learning within hours and lead to ‘diet-induced diabetes’. Type 2 diabetes is a multifactorial, long-term condition; reactive hypoglycaemia after a sugar load occurs in some individuals but is not a universal effect, so the page now states the cautious, well-supported position.

Sources: Mergenthaler, P., et al. (2013), Sugar for the brain — https://doi.org/10.1016/j.tins.2013.07.001 · full reference ›

Supported · moderate evidence — Dehydration impairs cognitive performance, including attention and short-term memory, so drinking water supports learning.

Wittbrodt & Millard-Stafford’s meta-analysis found dehydration (around 2% body-mass loss) significantly impairs cognition, with attention, executive function and motor coordination most affected; effects are reliable though modest, supporting the page’s water reminder.

Sources: Wittbrodt, M. T., & Millard-Stafford, M. (2018), Dehydration Impairs Cognitive Performance: A Meta-analysis. Medicine & Science in Sports & Exercise — https://doi.org/10.1249/MSS.0000000000001682 · full reference ›

Supported · moderate evidence — The drowsiness after a large meal is not caused by blood being diverted away from the brain, because cerebral blood flow is tightly regulated.

The ‘blood diverted from the brain’ explanation in the original page is a myth: cerebral blood flow is held roughly constant by autoregulation. The post-meal dip is better attributed to circadian rhythm, meal size and composition, and digestive signalling, so the page now removes the mechanistic overstatement while keeping the practical advice.

Sources: Mergenthaler, P., et al. (2013), Sugar for the brain — https://doi.org/10.1016/j.tins.2013.07.001 · full reference ›