Healthy brain food choices on a plate shaped like a human head. Healthy brain food choices on a plate shaped like a human head.

Fueling the Brain: Understanding Its Energy Needs and Sources

The brain is the most complex organ of the body. It performs the most complex functions and is the control center. Since this function is so prime, the cell density, primarily of the neurons, is very high. However, we need to work on improving its energy.

Do you know nerve cells are the kind of cells that require the most energy and are capable of consuming almost 50% of the body’s energy?

What is the Primary Source of Fuel for the Brain? Does the brain only use glucose to satisfy its energy requirements, or are there other substitutes also? I understand you are about to ask all these. I’ll highlight this topic further and try to answer all your queries.

Let’s Understand the Brain’s Energy Requirements

Although it accounts for only 2% of your body’s mass, its energy consumption is almost 20% of the total energy consumption of your whole body. Your brain requires high energy because of its functions. It has to maintain ion gradients, synaptic transmissions, and other vital processes.

Stable energy is required to perform these functions optimally, so let’s understand the mechanism of your brain’s functioning and energy metabolism.

 What is the Primary Source of Fuel for the Brain?
Source: Pixabay

Your brain’s functions, like thinking, learning, and memory, rely on glucose energy for efficient functioning. If your brain’s glucose level is insufficient, your messengers, neurotransmitters, aren’t produced. This leads to a loss of communication between your neurons.

Apart from neuronal computations, your brain’s energy is used for information processing, such as generating action potentials and other synaptic events. It also maintains ion gradients, which are necessary for neurotransmitter biosynthesis.

Your neurons require a lot of energy. Action potentials generated along axons and synaptic activity between neurons require significant energy. And signaling mechanisms during a synapse also consume considerable energy.

 What is the Primary Source of Fuel for the Brain?
Source: Pixabay

Glucose as the Primary Fuel Source

Glucose, metabolized via glycolysis, the tricarboxylic acid cycle, and oxidative phosphorylation, is your primary energy source. It is converted into adenosine triphosphate, which serves as your body’s primary energy currency.

A second important component is also responsible for the proper glucose uptake of your brain. So, insulin is the hormone that regulates glucose uptake, making it more available for your brain than the more peripheral parts of your body.

As we have seen above, it is a very important energy source for you, so much so that if the availability is higher, your brain’s performance improves. In adults, it leads to better memory.

You have seen that glucose is very necessary, but even then, there can be a chance that it is not completely available for your brain due to the blood-brain barrier that regulates what enters your brain.

In some cases, however, if your sugar level exceeds the required amount or goes below, these fluctuations can also impair your cognitive functions or affect your brain’s overall health, depending on whether it is hyperglycemia or hypoglycemia. Various studies have confirmed that prolonged hypoglycemia can cause functional brain failure, further leading to brain death.

The Icy Whiz team interviewed Lisa Richards, Nutritionist at The Candida Diet, and asked her about the brain’s energy requirements and primary fuel source. Here is what she had to say:

Lisa Richards
Lisa Richards

“Ketones and glucose serve as alternative sources of fuel for the brain, each with unique metabolic pathways and implications for brain function and energy metabolism. Glucose is the primary energy source for the brain under normal physiological conditions.

It is derived from carbohydrates and is readily utilized by brain cells to produce ATP, the energy currency of cells. Glucose metabolism is efficient and provides a quick energy source, supporting various cognitive functions, including memory, learning, and overall brain health.

On the other hand, ketones are produced when the body metabolizes fat in the absence of sufficient glucose, such as during periods of fasting, low-carbohydrate diets, or prolonged exercise.

Ketones can cross the blood-brain barrier and serve as an alternative energy substrate for the brain. While ketones may not be as efficient as glucose in energy production, they have been associated with neuroprotective effects, improved cognitive function, and enhanced brain resilience under certain conditions.

Both glucose and ketones play essential roles in brain metabolism, and the brain can adapt to utilize either fuel source depending on dietary and physiological conditions.

Switching between glucose and ketones as fuel sources provides metabolic flexibility and may confer various cognitive and health benefits. However, it’s essential to maintain a balanced and varied diet to support optimal brain function and overall well-being.”

Ketones as an Alternative Fuel Source

When glucose is less available in your liver, ketones are produced. This usually happens when you are fasting or during carbohydrate restriction. It happens to people with diabetes and also those with declining memory. The process of synthesis of ketones is called ketogenesis.

Ketones - word on wooden cubes on yellow background with stethoscope
Source: Depositphotos

These supportive extra energy-providing ketone bodies are short-chain fatty acids derived by the beta-oxidation of fatty acids. Their concentration in your blood and availability in the blood are in direct proportion.

They are oxidized in the mitochondria by oxidative phosphorylation in your neurons, generating ATP. The metabolism of ketones is also cognitively useful and provides better mental clarity and improved focus, specifically in people with neurodegenerative diseases.

The ketogenic diet consists of high fat, moderate protein, and low carbohydrate intake. This mimics a fasting state in your body, thus producing more ketones.

Low carb diet or ketogenic diet
Source: Depositphotos

The good availability of ketone bodies also improves memory retention and attention span. They are required not only as an energy substitute for glucose but also to support the anabolic energy requirements for cell growth, maturation, and proliferation.

They are essential for brain development and maturation before you become an adult or for a baby’s brain.

Dr. Mrinal Pandit, a registered dietitian, clinical nutritionist, and certified nutritional counselor at Oliva Skin and Hair Clinic, talked to the Icy Whiz team about the brain’s energy needs, specifically the roles of glucose vs. ketones. Here is what she said:

Dr. Mrinal Pandit
Dr. Mrinal Pandit

“Brain’s Energy Requirements and Primary Fuel Source

Energy Requirements
  • High Energy Demands: The brain accounts for a significant portion of the body’s total energy expenditure, despite its small size, due to its essential role in cognitive function, neurotransmission, and maintaining physiological processes.
  • Constant Energy Supply: Unlike other organs, the brain lacks energy reserves and relies on a continuous fuel supply to meet energy demands.
Primary Fuel Source

“Glucose is the main source of energy for the brain.” providing the energy needed for neuronal activity, neurotransmitter synthesis, and other metabolic processes.

  • Glucose Transport: Glucose is transported across the blood-brain barrier into brain cells via specific transporters, ensuring a steady fuel supply to meet the brain’s energy needs.

Role of Glucose in Brain Energy Metabolism

Glucose Utilization
  • Glycolysis: Glucose is metabolized through glycolysis, a series of enzymatic reactions that break down glucose into pyruvate, generating ATP for energy production.
  • Krebs Cycle: Pyruvate enters the mitochondria and undergoes the Krebs cycle, producing additional ATP through oxidative phosphorylation.
Neurotransmitter Synthesis
  • Precursor Molecules: Glucose metabolism provides precursor molecules for synthesizing neurotransmitters like dopamine, serotonin, and acetylcholine, which are essential for neuronal communication and cognitive function.

Implications of Alternative Fuel Sources like Ketones

Ketone Bodies
  • Ketogenesis: During periods of low carbohydrate availability or fasting, the liver produces ketone bodies (acetoacetate, beta-hydroxybutyrate, and acetone) from fatty acids through ketogenesis.
  • Energy Substrate: Ketone bodies can cross the blood-brain barrier and serve as an alternative fuel source for the brain when glucose availability is limited.
Brain Adaptation to Ketones
  • Ketone Utilization: With prolonged ketosis, the brain adapts to utilize ketones more efficiently for energy, sparing glucose for essential functions and reducing the brain’s reliance on glucose.
  • Neuroprotective Effects: Ketones have been associated with neuroprotective effects, including reduced oxidative stress, inflammation, and improved mitochondrial function, which may benefit brain health and cognitive function.

Impact of Dietary Factors on Brain Energy Metabolism

  • Glucose Availability: Carbohydrate-rich foods provide the glucose needed to fuel brain energy metabolism, supporting cognitive function and mental clarity.
  • Blood Sugar Regulation: Consuming carbohydrates in the form of complex carbohydrates (whole grains, fruits, vegetables) helps maintain stable blood sugar levels, preventing energy crashes and supporting sustained brain function.
  • Ketone Production: Dietary fats can contribute to ketone production through fatty acid oxidation, providing an alternative fuel source for the brain during ketosis.
  • Omega-3 Fatty Acids: Omega-3 fatty acids found in fatty fish, flaxseeds, and walnuts have been associated with improved cognitive function and may support brain health and energy metabolism.
  • Amino Acid Precursors: Protein-rich foods provide amino acids that are precursors for neurotransmitter synthesis, supporting neuronal communication and cognitive function.
  • Glucose Production: Excess protein can be converted into glucose through gluconeogenesis, providing an additional source of fuel for brain energy metabolism when needed.”

I’ll Tell You More About the Primary Source of Fuel for the Brain

As we have seen above, glucose is the primary source of energy, and it is obtained from sugar or carbohydrates.

Our brain is a very important part of the body, essentially the organ that maintains and controls all functions. It is necessary to ensure that when there is a lack of glucose in the body, there has to be an alternative because the brain’s work can essentially never stop.

In such cases, ketones, which are synthesized by fatty acids instead of carbohydrates, are used.

Top view of arrangement of food for brain and memory, healthy eating concept
Source: Depositphotos

The brain’s workings are essential to the processing of our body because it performs all its functions and directs and governs the body. So, the cells in the brain, mostly neurons that have to perform so much, also have a very high energy requirement, which is fulfilled by glucose and sometimes ketones.

In an interview with the Icy Whiz team, Billy Litmer, Founder of Honest Eco Tours, emphasized the role of carbohydrates in supplying fuel to the brain. Here is what he said:

Billy Litmer - Featured
Billy Litmer

“The brain’s primary fuel source is carbohydrates, broken down into a form of sugar known as glucose. This is why glucose is considered the main energy source for the brain.

Because of this, low-carb diets might not be the most beneficial for brain health. If you don’t consume enough carbohydrates, you deprive your brain of its preferred fuel source.

Even though producing ketones isn’t necessary for optimal brain function, it can be beneficial. Typically, the brain uses about 22% of the total energy we consume, all of which can come from glucose.

However, if ketones are present in the system, the brain may preferentially use them, indicating that neurons may perform well on ketones.

Nevertheless, on a standard low-carb diet, the brain will still primarily rely on glucose, the sugar circulating in your bloodstream, for energy. Yet, the brain may utilize more ketones than a regular diet.

On a ketogenic diet, where carbohydrate intake is extremely low, ketones become the main energy source for the brain. The liver produces ketones during this process, and low-carb diets fuel the brain through ketogenesis and gluconeogenesis.”

Brain and Its Source of Energy

The brain needs a lot of energy to work well. It mostly uses glucose, which comes from sugar and carbs, as its main fuel. But when glucose is low, like during fasting or dieting, the brain can use ketones, which come from fats, as an alternative.

This is important because the brain never stops working and needs a constant energy supply. Whether from glucose or ketones, giving the brain enough fuel is crucial for keeping it running smoothly and keeping us thinking clearly.

Last Updated on May 18, 2024 by Pragya


Anushree Khandelwal
  1. Learning about how the brain gets its energy was really interesting. It mostly uses glucose, like sugar, but can also use ketones when glucose is low. Understanding this makes me appreciate how important it is to keep our brain fueled for its many functions. This article was really informative.

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