Glucose or Ketones: The Brain Follows a Rhythm

Glucose or Ketones: The Brain Follows a Rhythm

by Laurent Glatz – for Athletic Carnivore

Spotify Link: https://open.spotify.com/episode/0gvdqrigDs52uKEzWNyvQs

The real issue isn’t deciding which fuel is morally or nutritionally “better.” The real issue is forgetting that the brain operates through metabolic alternation. During wakefulness, stress, effort, decision-making, or nervous activation, it shifts into a mobilization mode where glucose strategically becomes dominant again. During rest, recovery, parasympathetic calm, and especially sleep, it returns to a ketone-rich environment more favorable for building and repair.

Popular belief holds that the brain needs a continuous supply of glucose. The actual mechanism is more demanding: it requires flexibility. Keeping it permanently in glucose mode traps it in urgency. Locking it into permanent ketosis denies its adaptive logic.

The Modern Brain Is Often Misinformed

This metabolic switch is governed by hormones, not dietary dogma. Cortisol acts as the mobilization switch. Upon waking, it surges sharply—sometimes increasing by 50 to 150% within 30 to 45 minutes—to pull the body out of a building mode, stimulate gluconeogenesis, mobilize glucose, and activate the sympathetic nervous system.

Insulin determines the degree of access to fats and ketone production: when high, it inhibits lipolysis; when low, it allows ketogenesis to rise. Leptin is supposed to inform the brain about energy reserves, but in a context of food overstimulation and chronic energy excess, this signal becomes blurred. Ghrelin drives hunger when the body senses a need, but in an environment where blood sugar constantly rises and falls, hunger often ceases to be a reliable indicator and instead becomes a symptom of metabolic disorder.

In other words, the modern brain is not only poorly nourished; it is poorly informed.

When Glucose Becomes a Permanent Emergency

When blood sugar is constantly demanded, insulin remains elevated too often, storage is favored, access to ketones diminishes, and the body stays oriented toward mobilization rather than repair. In the short term, this causes energy fluctuations, false hunger, sugar cravings, mental fog, and dependence on quick energy sources. In the long term, this environment promotes hyperinsulinemia, low-grade inflammation, loss of metabolic flexibility, and increasingly impaired satiety signaling.

Conversely, ketones are not just an alternative fuel: they are part of a maintenance biology, providing a more stable environment for nerve recovery, neurogenesis, myelination, autophagy, protein synthesis, and cellular repair.

The essential point is this: the brain was not designed to be fed continuously, stimulated without pause, and kept relentlessly in a glucose-alert state.

The Real Issue: The Hormonal Rhythm

The contradiction in current recommendations becomes obvious. We claim to protect the brain by ensuring constant carbohydrate intake, while often perpetuating exactly what undermines its energy stability, satiety, and ability to alternate between mobilization and construction.

An efficient brain is not an overfed brain. It is a brain capable of entering action when cortisol demands it, then returning to a low-insulin state to rebuild what the day has broken down. The real question is not “glucose or ketones?” but rather: what hormonal state do you live in from morning to night, and how many hours do you still allow your brain to escape modern metabolic urgency?

#Brain #Glucose #Ketones #Cortisol #Insulin #Leptin #Ghrelin #MetabolicFlexibility #MetabolicHealth #CognitivePerformance