Glucose vs. Ketones: Which is Best for the Brain?

Ketosis is a metabolic state where the liver takes proteins and fat and allows molecules to use them for energy.

Ketosis allows a starving person to survive for days (or even months). Some athletes see changes while others feel miserable whenever they are in a ketogenic state.

That said, is a ketogenic diet ideal for you?

Ketogenic Diet and the Brain

Your brain is about 2% of your body mass, even though it needs about 20% of your basal metabolic rate, more if you are a thinker.

Different parts of your brain use different amounts of glucose, and almost twice as much in the morning. You will need to fuel your mind more if you have your mind working hard throughout the day and solving problems.

If you’re working more on engine control (state a skill requiring precision or equilibrium), you will use less glucose. Many people can attest to how significant energy is used by the brain when tested.

Although sugar is run off by our brains rather than fat, they can also run off of ketones as an alternative fuel source. People who market diets tend to be wary that an increase in ketones develops repair and healing of neurons. It also increases the neurotransmitter GABA.

GABA makes it possible to sleep. It’s also the primary neurotransmitter that influences sleep and antipsychotic drug influence.

Due to the influence of ketones on the brain, a ketogenic diet can help those with seizures. Of course, ketosis indicates you’re burning far more fat for energy.

You won’t bet on some harmful diabetic ketosis amount as long as you produce even only a tiny amount of insulin. So as long as you are not Type 2 or Type 1, there is nothing to fret about immediately.

However, to stay in a ketosis state, you typically require to eat less than 50g of carbs per day, if not less than that. In this state, the body’s functions are fat-based instead of glycogen, and the brain is based on ketones instead of glucose.

People wanting to achieve ketosis can not consume an excessive amount of protein. This implies no more than 150g per day. Protein could be converted into glycogen and can also be used to make glucose, and you would throw the body out of ketosis.

What are Ketones?

David Nazarian, MD, defines Ketones as “water-soluble particles” produced by the liver. They are made from fatty acids when your body does not create sufficient insulin to turn glucose into energy.

Simply put, ketones (or ketone bodies) are an alternative fuel source. When your body doesn’t have adequate sugar or glucose for energy, your body will require a new energy source. Your body will then shift to breaking down fat for energy.

This method is done in the liver, where fats are turned into a chemical called ketones. The ketones are then discharged from the liver and go into your bloodstream. They are used as fuel to push the body’s metabolism and to support muscle function. 

The body typically requires ketones when insulin levels are low. This usually occurs during fasting, eating low-carb diets, or when sleeping. 

In uncontrolled type 1 diabetes, ketones may be produced due to a shortage of insulin-producing beta cells of the pancreas.

Measuring ketone production can be performed with urine testing. The safe measure of ketones in urine varies from person to person and depends on their underlying health situations.

While some people can produce ketones in their urine, others should be bothered if there is a ketone build-up. That’s because this could be suggestive of a more severe problem.

Are Ketones Dangerous?

It’s not typically an issue for people who are not having diabetes when your body creates ketones. However, for people with diabetes, ketones can be very risky. This is because the body can’t control insulin, glucagon, and other hormones in those with diabetes. 

“High levels of ketones can be hazardous and can cause health problems. Dangerously, high levels of ketones in our bodies usually happen in insulin-dependent diabetic type 1 patients who do not intake their insulin,” said Dr. Nazarian, “It can lead to dehydration and can also turn the chemical balance of your blood. Your blood becomes more acidic which if not treated immediately can lead to a coma or death.”

If your levels are low-moderate, call your doctor to address these levels to receive further testing. Your doctor will likely run a urine or blood test to determine ketone levels and perform a blood sugar test at your visit.

For levels greater than 1.6, it is essential to seek medical attention as symptoms could be life-threatening. 

How to Test Your Ketone Levels

There are three different ways of testing your ketone levels — blood, breath, and urine. Of all three methods, blood ketones are the most accurate because they interpret what you’re body is currently working with. 

Urine testing is only helpful in the first stages of keto-adaptation when your body is still learning how to utilize the ketones you’re creating. A good piece of the ketones you produce will get drained out through your urine during this time. This can give you insight into whether or not your body is creating ketones. 

However, over time, your body will become more accustomed, and the number of ketones lost in your urine will reduce. 

Breath testing is an excellent way to examine and is much less invasive than blood testing, but it may be less accurate. 

Either way, understanding your ketone levels is an excellent way to determine if your diet and lifestyle changes are working.

There are several methods to test your body for ketones. You can get the tests done in a lab, but there are faster and more affordable alternatives.

Your ketone levels can be anywhere from zero to 3 or higher. They are measured in millimoles per liter (mmol/L). Below are the general scales, but keep in mind that test results can vary depending on your diet, activity level, and how long you’ve been in ketosis.

  • Negative ketone level: less than 0.6 mmol
  • Low to moderate ketone level: between 0.6 to 1.5 mmol
  • High ketone level: 1.6 to 3.0 mmol
  • Very high ketone level: greater than 3.0 mmol

Now, let’s go over the different ways for testing and the pros and cons of each:

Urine Testing

Method: You pee on a urine strip, which symbolizes the level of ketones by color.

Pros: You can purchase the strips at most pharmacies or online for a low cost. This is an affordable and accessible substitute for someone new to the ketogenic diet.

Cons: Urine test strips aren’t as reliable the longer you’ve been in ketosis. That’s because the longer a person is in ketosis, the more efficient the body is in using ketones for energy.

Therefore, the test can show a lower level of ketosis than you’re actually in.

The urine ketone readings can also be altered by other factors, including the level of electrolytes in the body or how hydrated you are.

Blood Testing

Method: With a blood glucose meter, you apply a lancet pen to press onto your fingertip and draw a small blood sample. The blood used on a test strip observes blood ketone levels through the meter.

Pros: This is a very accurate means of ketone monitoring since few factors alter the results.

Cons: It can be expensive, especially if you test regularly. Cost is often $5-10 per strip!

Note: The ketone BHB is transported through the blood, so this is the best way to observe your levels of that specific ketone.

Breath Testing

Method: You use a Ketonix breath meter to examine the amount of acetone present on your breath.

Pros: It’s affordable after buying the meter. Once you purchase it, you can use it continuously without extra charge.

Cons: It’s not the most reliable testing process, so it’s best used in conjunction with other methods.

What if My Ketones are Too High?

Handling high ketone levels can help you avoid Diabetic Ketoacidosis (DKA).

Work with your doctor to determine what you need to do to help manage moderate ketone levels. If you’re incapable of treating at home or if your levels continue to climb, you’ll need to receive medical treatment.

Treatments can incorporate:

Intravenous (IV) fluid replacement

One DKA symptom is prolonged urination, which can result in fluid loss. Rehydrating with IV fluids can help to reduce the extra glucose in your blood.

Electrolyte replacement

When a person has DKA, their electrolyte levels direct downwards. Examples of electrolytes involve potassium, sodium, and chloride. If a person spends too much of these electrolytes, their heart and muscles can’t function as well.


In an emergency, people are usually given insulin through an IV. This is to increase their ability to use excess glucose in the blood for energy. It also includes testing glucose levels on an hourly basis.

When your ketones and blood acid level normalizes, IV insulin may no longer be necessary. And you would continue your regular insulin therapy regimen.

DKA can also be caused by an underlying ailment, such as an infection or a severe stomach bug that causes vomiting. In these cases, your doctor may prescribe treatments for the underlying condition as well.

What is Glucose?

Glucose is the primary sugar in your blood. Carbohydrates from the food you eat become transformed into glucose.

Glucose is necessary for that it gives the energy of your organs that they can immediately utilize. It enables you to perform an intense workout and lets your body create other molecules like collagen.

Glucose also serves as brain fuel.


Glucose helps you complete challenging mental tasks

Your brain spends 10.8 calories in one hour to perform its tasks. That’s how energy-hungry the brain works.

The more challenging the mental duty is, the more glucose it needs. Usually, such tasks are those that you may not be very good at and require you to think. Scientists recommend that eating sugary foods should increase the performance of these tasks. 

Glucose increases the attention span of children

Considering general knowledge, we can say that glucose helps us refocus when we feel exhausted. For example, during a pause between exams, having a sugary drink puts us back into action.

One study observed 60 six and seven-year-old children. As the end of the school day neared, they were given a drink. That drink carried either 25 grams of glucose or a placebo. Results revealed that those who had the glucose-filled drink were able to support their attention for longer.


Habitual sugar consumption may increase depression risk

Sugar is such a controversial subject. It’s on the list of factors that are likely to add to depression.

Too much sugar, especially sugar found in soft drinks, juices, and pastries, reduces your brain-derived neurotrophic factor (BDNF).

If you don’t know what BDNF is, it’s a protein that supports and promotes your neurons’ growth. Brains of patients who are depressed show reduced activity of BDNF. This could tell the link between high sugar intake and depression.

Sugar triggers the reward centers of the brain connected to addiction

A 2018 research examined the influence of sugar on obesity, a medical condition that strikes millions of people worldwide. It’s no secret that sugar is found in the highly processed, inexpensive, and convenient foods we ingest. But how does sugar add to obesity?

Sugar is an addictive element as it boosts your brain’s reward circuit that’s connected to addiction. In effect, you always want to endure the pleasure of eating sugar. It becomes a habit.

The same study showed that sugar dependent rats increased their intake of alcohol. Neurochemical similarities were also observed among sugar dependent rats and those who misused drugs.

Ketones vs. Glucose

So, should you strive to achieve this ketogenic state? For many people, they need to do it at least to turn their body from insulin resistance.

Again, like most things, it is highly individualized. If you’re incredibly resistant, this might be your way out of it and about the road to health again.

Overall, most people could do much better (significance become fitter and more healthy), consuming fewer carbs. But when they don’t need to, some people incline to go to stress and extreme carbs.

Many people also fear insulin. That’s because everything we read about obesity, cancer, and other ailments talks about insulin and inflammation.

But remember, it is all about obtaining just the right amount. Insulin is not a dangerous guy; just too much of it is. If you don’t get insulin when you ought to be, you’re really in a more desperate situation than becoming insulin resistant.

It typically takes two to three weeks to turn your body over to fat from using glucose as the primary fuel source, with a very low carb, high-fat diet plan. Merely squeezing your diet a little bit won’t do the job. You have to be intense for a few weeks and then take in carbohydrates to determine how your body reacts to them.

The nice thing about turning your body from sugar burning is that you won’t revert to this routine. Whether you want to be in ketosis or not is your decision, but you should be ready to go days with no carbs (other than veggies) in your diet plan.

You should only consume carbohydrates when you only want to eat them. Remember, even if you’re only consuming about 2,000 calories per day, then 100g of carbohydrates is only 20% of your diet plan.

You’re getting an equal amount of protein, and that leaves the fat around 60%.

You are going to require some more carbs if you are training hard. Therefore, if you are going to attempt a diet, do it in the offseason. For example, when you’re in a recovery period in racing or training hard.

On a clinical note, many people perform well staying in ketosis for more than a month or two months, max. Health disorders and pain have been a consequence of being in a ketogenic condition for such a long time.

The diet helps people improve mentally and physically, but it can turn on them without proper knowledge. Therefore, have to pause every few months or so if you’re going to go keto. This is to see how you perform and feel in and out of ketosis.

Glucose Metabolism (Glycolysis)

Dietary glucose is achieved through the digestion of carbohydrates in the stomach and small intestine. It is further broken down through the method of glycolysis.

Through a sequence of steps, glucose is broken down into pyruvate and acetyl-CoA. Acetyl-CoA enters the TCA cycle (tricarboxylic acid cycle), which is also recognized as the citric acid cycle (CAC) or Krebs cycle.

For each glucose molecule that sustains glycolysis, there is a net increase of 2 ATP molecules, 2 NADH molecules, and 2 pyruvate molecules (technically 4 ATP are generated, but 2 are used).

Glucose Transport into the Brain

Glucose is carried in the blood and passes through the blood-brain-barrier via glucose transporters (GLUT). This is to provide the brain with energy.

Both GLUT1 and GLUT3 transport glucose in the brain. However, GLUT 3 is the most overflowing, making it predominantly a response for glucose transport into the brain.

Energy for the brain is constructed from glucose breakdown and the formation of ATP. 

Ketone Metabolism (Ketogenesis and Ketolysis)

When carbohydrates are limited, and insulin is lowered, fatty acids are mobilized. These free fatty acids (FFAs) are broken down into acetyl-CoA inside the liver. High levels of acetyl-CoA lead to ketone bodies’ production (acetoacetate, acetone, and beta-hydroxybutyrate). This method is known as ketogenesis. The liver releases ketones into the bloodstream, where they can travel to the brain.

Ketones can then be broken down into acetyl-CoA, which feeds into the TCA cycle to produce energy (ATP). This method is known as ketolysis.

Ketone Transport into the Brain

The brain takes up BHB (beta-hydroxybutyrate) via Monocarboxylate Transporters or MCTs.

BHB is turned into acetoacetate and then into acetoacetyl. Acetyoacetyl can then be turned into acetyl-CoA before entering the mitochondria.

This is where it enters the TCA cycle and leads to ATP (energy) composition.

Final Thoughts

You might wonder which between Ketones and glucose can fuel your brain thoroughly.

Based on the studies above, ketones make a more reliable fuel source. Beta-hydroxybutyrate (BHB), the richest ketone body, acts as a more effective fuel than glucose.

More research also shows that the brain can benefit from ketones. Hence, a low-carb diet is suggested to people with Alzheimer’s, epilepsy, and traumatic brain injury.

While the brain operates on glucose, it uses ketones as an alternative whenever there’s a glucose deficiency. If you’re thinking about making the shift from glucose to ketones as brain fuel is worth it, consider the points we discussed above.

Glucose is necessary, and that’s true. However, too much glucose in the blood causes more harm than good.

We live in an age that adopts convenience, and with that, most of our convenient food options carry loads of sugar. Sugar is connected with health problems like depression and obesity.

Nonetheless, if you plan to begin a keto diet for brain health, be sure to consult with your doctor first.