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Does the Brain Need Carbohydrates?

It is known that carbohydrates are necessary for the brain to operate. This could appear to be a strong rationale for not pursuing a full ketogenic diet. But is it true? Continue reading to find out the reason why your brain continues to operate when you give up eating carbs, or click on the links above to quickly go to a particular part.

Your Brain Needs a Constant Energy Supply

It could be argued that your brain is the most active organ in your body. This allows you to think, talk, and carry out a lot of activities right away.

It takes responsibility for several involuntary activities essential for staying alive, such as inhalation, tempering the body temperature, and producing hormones. This area acts as the control center of the central nervous system, getting and sending signals throughout your body that enables you to identify a car that hastily moves into your path and then either hit the brakes or dodge away in order to avoid it.

Despite its relatively small size, the brain uses up a fifth of the energy you consume each day although it only makes up two percent of your body mass.

The brain needs a consistent supply of energy in order to perform its essential tasks. The brain is capable of employing two primary sources of energy, namely glucose and ketones, both of which are able to pass through the blood-brain barrier.

The primary fuel for the brain to use is glucose for individuals who have a diet that is composed of moderate to high amounts of carbohydrates. Those who eat a low-carb, ketogenic diet will have their brains utilizing ketones to satisfy a large part of its energy needs.

What happens when you don’t eat any carbs?

It is thought that the brain needs somewhere between 110-145 grams of glucose from carbohydrates in our food everyday to work properly. Most people consume two-fold the amount of carbohydrates in comparison to the amount their brains require, leaving them with an abundance of glucose.

What would occur if you consumed much less than 110 grams of carbohydrates per day, or even none at all? Does the brain starve? Not!

Your liver and muscles keep glycogen, which is a form of glucose, stored. The quantity fluctuates depending on the individual, but the average weight for a man of 154 lbs (70 kg) tends to reserve around 100 grams of glycogen in the liver.

After a period of not consuming carbohydrates, the liver breaks down its glycogen stores and releases the glucose into the bloodstream so that the blood sugar level does not go below the desired amount. Glycogen is stored in much greater quantities in the muscles than it is in the liver. It stays in the muscles in order to provide them with energy, and it cannot be converted into glucose in the blood.

After going through a period of two days to two days and a half without carbs, the stores of glycogen in the body get used up, and the hormone insulin drops (particularly when more strenuous activity is undertaken).

At this juncture, the liver raises its generation of water-soluble compounds referred to as ketones, made by the decomposition of fatty acids. You can create ketones by using the fat found in food or the stored fat in your body. Ketones created because of this process can pass through the blood-brain barrier, allowing the brain to obtain additional energy.

This implies that there is an alternative energy source for the brain to utilize when the body’s supply of stored carbohydrates is depleted.

Can Your Brain Rely on Ketones Alone?

The brain always requires some glucose. Studies have demonstrated that for certain people who are sticking to a precise ketogenic diet, ketones can supply as much as 70% of the brain’s energy can use.

For the rest of the brain’s energy demand, the liver can generate all the glucose needed with a procedure known as gluconeogenesis (literally “forming new glucose” ).

Compounds that the liver uses to synthesize glucose include:

  • Amino acids from eating protein (or, under conditions of inadequate protein intake or periods of starvation, from muscle breakdown.)
  • Glycerol (part of a triglyceride molecule) from the breakdown of body fat or dietary fat.
  • Pyruvate and lactate, are molecules that form when the body metabolizes glucose. These molecules can be joined back together to re-create glucose.

Your brain can obtain all the energy it needs from the liver regardless of whether or not you eat carbohydrates, either from glucose storage, the creation of new glucose, or the production of ketones.

Indeed, the US Food and Nutrition Board’s 2005 textbook “Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids,” states that:

No minimal amount of carbohydrates must be consumed in order to maintain life, as long as the daily intake of protein and fat are sufficient.

Using glucose alone vs. glucose and ketones for brain fuel

If your diet consists of a moderate to high amount of carbohydrates, your brain is not conditioned to use ketone bodies as a form of energy. Therefore, the brain will primarily rely on glucose as its fuel.

When the body has gotten used to consuming an extremely low-carb or no carb fare, the brain obtains a lot of its energy from ketones, and the liver produces just the right amount of glucose to satisfy the rest of the body’s requirements. Therefore, the amount of glucose in the bloodstream stays consistent, and the brain is still supplied with energy, despite the fact that carbohydrates are not ingested.

This makes perfect sense from an evolutionary standpoint. Hunting and gathering societies are aware of how lengthy the process of tracking down food can be, sometimes leading to long stretches without meals for multiple hours or days. Being able to employ the coupling of ketones and glucose to provide sustenance for their brains was likely essential for their endurance.

Are Ketones Good for Brain Health and Function?

Some experts hypothesize that the combination of ketones and glucose can be particularly effective for the brain when applied to people with neurological and mental health issues. Investigation indicates that this pairing would be of great help in some circumstances.

Let’s take a look at some of these circumstances:


Though not always completely carb-free, the typical ketogenic and adapted Atkins diets keep carbohydrate consumption below 20 grams per day. Research suggests that restructuring carbohydrate levels can be remarkably beneficial when dealing with seizures in both children and adults. Tests have shown that it can even lead to the complete absence of seizures.

Mental health conditions

Initial research, along with reports and experiments that back it up, as well as a few clinical trials with promising results, suggest that a ketogenic diet could be beneficial in managing some mental health issues.

An illustration of this may be seen in bipolar disorder, which is similar in some respects to epilepsy, and may get better when given a ketogenic diet, just like schizophrenia. Check out our guide to learn more about the link between low-carb diets and mental health.

Why Humans Don’t Need Dietary Carbohydrates to Thrive

When discussing carbohydrate restriction, two fallacious arguments related to the energy needs of the brain and the sustainability of a ketogenic diet are often levied against the use of a well-formulated ketogenic diet in practical therapeutic medicine:

  1. The human brain burns 600 kcal per day, and this translates to a 150-gram per day glucose requirement to meet its energy needs, and
  2. No one can follow a ketogenic diet long term.

For the past 50 years, studies conducted by medical experts have disproven objections to the safety and sustainability of the ketogenic diet. This was recently highlighted by the success of the two-year Indiana University Health study.

We have gone over the elements of an effective ketogenic diet that most people can sustain if they are well-informed and have the right support. We are aiming to discuss in this area how a diet low in carbohydrates and with little or no carbohydrates can be as successful—or possibly even more successful—than the commonly recommended ‘healthful diet’ that is low in fats and contains lots of carbohydrates.

Research has demonstrated that molecules generated from dietary fats or fat deposits accumulated in our adipose tissue are magnificent energy sources for the brain. We are now aware that ketones created by the liver have multiple advantages for the heart, kidneys, and other body parts, and this probably leads to a longer life.²,³,?. Research has recently brought to light that glycogen replenishment and performance of even strong, competitive athletes is not completely reliant on a diet which is high in carbohydrates.

Until 5 years ago, the exact processes that caused extra positive impacts were challenging to comprehend. Now, it is evident why disregarded anatomy can be a major factor in our health and happiness. Aside from ketones being less destructive to our body because they create fewer harmful byproducts than glucose when used by our organs, the main ketone beta-hydroxybutyrate can even act as an indicator to switch on genes that control our protection against oxidative stress and inflammation.

It is quite complex the way in which the body transitions from using carbohydrates as the main energy source to relying on fatty acids and ketones. The term “keto-adaptation” is used to describe the process wherein individuals become accustomed to a ketogenic diet. The transition typically begins within a few days but can take an extended length of time to be completed. After it is fully finished, the outcome is not a total barring of sugar from the body’s energy source. Glucose demand and use is hugely decreased, with other metabolic outlets such as pyruvate and lactate being used to restore energy and other vital metabolic components. This leads to the steadiness of ordinary blood sugar and muscle glycogen levels that can be kept up without needing to consume dietary carbs.

Physiologic Role of Carbohydrates

The commonly held notion of the brain’s dependence on carbohydrates for proper operation is sometimes reinforced by the idea that since the brain functions with glucose, it must thus require this glucose on account of that fact. The flaw in this argument is that glucose is not essential for the brain’s functioning. It functions quite well on ketones. Put differently, the supposed necessity for glucose by the brain is reliant on the fuel sources that somebody compromises on when they select their diet. A diet that is high in carbohydrates and protein that makes up more than 30% of the energy intake will make the brain use glucose as its primary source of fuel.

Some cells within the body do indeed require glucose. An illustration of this would be red blood cells, portions of the kidney, and the epithelial cells that enclose the lens of the eye, which primarily rely on glycolysis because they don’t possess mitochondria and as a result, depend on glucose to operate. It holds true that the fast-twitch muscle fibers employed in activities such as weight lifting and sprinting have fewer mitochondria when compared to the slow-twitch muscle. In all of these scenarios wherein glucose is oxidized to lactate, the body has an option to make. Cells with mitochondria can further break down the lactate to carbon dioxide and water, or the organism can restore the lactate to glucose.

Evidence That the Brain Can Function on Ketones

Observing humans, it can be determined that their brains can carry out normal mental functions for a period of 1-2 months even if they haven’t eaten anything, which is evidence of their capacity to survive on ketones. It is interesting to note that when an individual is starving for an extended period of time, they suffer a decline in their muscle mass and capacity of other crucially important physical components. The brain is not affected at all by the body’s metabolism that is triggered by hunger and results in a reduction of resources. Results of sophisticated investigations that looked into the amount of glucose and ketones in the blood that enters and exits the brain showed that ketones are capable of providing the majority of energy that the brain needs. Despite extended periods of fasting, the blood glucose level remains within the ‘routine’ range; therefore, these observations did not disprove that the keto-adapted mind needs a bit of glucose to function.

The question of how mental function is affected when blood glucose is drastically reduced was investigated many years ago by two distinguished research teams. This was done by running experiments on people who had adapted to a starving state, and reducing their blood glucose with an infusion of insulin.

For both investigations, heavily overweight people who had not eaten anything and were constantly monitored while staying in a hospital for between 30 and 60 days were studied. Drenick et al. examined nine individuals who had a concentration of BOHB in the 7–8 mM range; intravenous insulin was then given to the participants in order to decrease their blood glucose to an average of 36 mg/dl (with some achieving as low as 9 mg/dl). Although the hypoglycemia was extreme enough to be linked to coma or death, none of the patients experienced any indications of low blood sugar. Furthermore, although blood glucose levels dropped intensely but briefly, levels of urinary catecholamines that indicate the body’s resistance against low blood sugar were not elevated.

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