Your brain – one of the most energy demanding organs inside your body. To function properly, it needs to have access to a constant fuel supply. But how much glucose does the brain need? Let’s find out.

Burning Glucose or Energy

Comprising about less than 2% of your total body weight, the brain consumes roughly 20% of your daily calories (1). It’s one hungry beast and for a reason.

Without you knowing it, your brain is constantly carrying out countless processes linked to the nervous system, processing of sensory data, storing memories, regulating homeostasis, and making decisions. Even while you’re sleeping, your brain never really shuts off completely and is continuously burning energy. Imagine the analogous electrical bill at the end of the month…

The body’s primary fuel source is glucose that’s a sugar molecule. There are other alternatives to glucose but the brain, heart, and some other organs need exclusively glucose for initiating certain biosynthetic processes.

Does the Brain Need Glucose

The brain uses about 120 grams of glucose daily (2) and its functioning begins to become seriously affected when glucose levels fall below 40mg/dl. Fatty acids cannot be used for energy by the brain because they do not cross the blood-brain barrier.

However, because in nature glucose isn’t always easily found or readily available, our bodies have developed many pre-cautionary adaptations for the absence of glucose.

Fatty acids need to be converted into ketone bodies first before they can be used for energy by the brain. There is 3 type of ketone bodies: acetoacetate, acetone, and beta-hydroxybutyrate, the latter of which can be directly used for fuel by muscle as well as brain tissue.

After proper keto-adaptation, the brain can cover 50-75% of its energy demands with ketone bodies (3). Usually, ketone bodies are produced by the liver in a state of glycogen depletion but research has found that the astrocytes in the brain and spinal cord can also produce ketone bodies, which can be used as substrates for neuronal metabolism and have neuroprotective effects (4).

Are Ketones Enough

It’s clear that ketones are an effective fuel source for the brain in states of starvation and energy deprivation i.e. while you’re fasting, when you’ve depleted your glycogen stores or on a calorie restricted diet.

Given that ketones can provide up to 50-75% of the brain’s energy demands, you’ll still need about 30 grams of glucose to cover the remainder of its necessary fuel.

However, that doesn’t mean you need to be consuming carbohydrates or glucose to give your brain the glucose it needs.

During a process called gluconeogenesis, the liver can take a triglyceride molecule (fat) and break it into 3 fatty acid chains and a glycerol molecule that binds them together. The fatty acids will be burnt off as energy in the bloodstream and the glycerol will be converted into glucose to fuel the brain and other vital organs.

For the brain, there’s no difference between glucose that you get from eating carbohydrates vs creating it through gluconeogenesis – glucose is glucose once it gets to the right place.

Ketones VS Glucose

If you don’t eat carbohydrates, how will your brain get the energy it needs? That’s a common question I get when I tell them about the ketogenic diet and carb restriction. Why would you want to do that if your brain needs glucose? That’s a valid point.

Even though glucose is needed in some amounts, too much of it will become damaging to the body. There is a lot of evidence showing that many metabolic diseases, obesity, diabetes and cognitive decline are linked to excess sugar consumption. Although it’s not conclusive (5).

Alzheimer’s disease is now being referred to as type-3 diabetes (6), as it’s caused by an energy crisis in the brain. Insulin resistance in the brain contributes to the development of cognitive decline (7) and people with type-2 diabetes have an increased risk of Alzheimer’s of 50-65% and higher.

There’s also the fact that glycolysis – carbohydrate metabolism – causes more oxidative stress to the mitochondria and create reactive oxygen species that lead to inflammation (8).

Ketones are a much cleaner fuel source for the brain and mitochondria as they can be transported quicker through the Krebs cycle and they leave less metabolic waste.

Is Glucose Even Needed by the Brain

There’s also evidence that the brain can run on lactate, especially during intense exercise. Lactate is the metabolic byproduct of muscle glycogen metabolism.

The brain prefers lactate over glucose (9), probably because of not wanting to waste any readily available fuel just lying around there. This is further evidence that you don’t need to be consuming 120 grams of carbohydrates every day as your body has many alternatives for it.

You don’t even need to be eating anything at all as during prolonged fasting glycerol can contribute up to 21.6% of glucose production (10). Glycerol can come from both dietary fat intake as well as your own stored body fat.

There’s recent research showing that in vitro using fuel substrates other than glucose improve neuronal efficiency and oxidative metabolism (11).

How Much Glucose Does the Brain Need

It doesn’t mean carbohydrates or glucose are bad – quite the contrary. However, as we’ve said, you don’t need to eat carbs to fulfill that demand and more isn’t necessarily better. High levels of blood sugar and chronically elevated insulin are one of the important things for overall health and cognition.

Let’s do some math here then

At minimum, your brain needs about 120 grams of glucose

After keto-adaptation, you can cover 50-75% of the brain’s energy demands with ketones instead. That leads us to at least 30 grams of glucose that the brain still needs.

Glycerol from fatty acids can contribute up to 21% of glucose production, which leads us to about 25 grams of glucose from glycerol.

Gluconeogenesis of amino acids or lactate will probably produce more than a few grams of glucose.

Eating low carb vegetables and other foods will also provide more than enough carbohydrates and glucose for the entire body.

Therefore, if you give your brain an efficient solution to its energy demands, then you can get all the glucose you need and much more.

The Energy Efficient Brain

If Alzheimer’s and cognitive decline are caused by a fuel crisis, then making your body more efficient at producing its own fuel despite the presence of dietary carbohydrates or other foods is the smart thing to do.

You don’t want to give your body anything in excess – not too many carbohydrates, not too much protein, not too much fat, not too much stress, and not mental inaction either.

The key to longevity and functionality is keeping yourself sharp and active. To maintain good cognition and keep your brain properly energized, you need to feed it the right fuel in the right amounts.

How many carbohydrates you choose to eat based on this article depends on many other factors but know that you can thrive on zero carbohydrates and you can thrive on eating more than 120 grams of carbohydrates. Just make sure that you’re not consuming random carbs and that the carbs you do eat are used efficiently.

Feed Your Brain

If you want to know what foods to feed your brain with then read this post.

I also have my KETO // IF program that optimizes your physiology to becoming insanely keto-adapted by combining the ketogenic diet with intermittent fasting. Check it out!

Stay Empowered

Siim

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