Why carbs aren't essential for brain function

By The Low Carb Clinic, 4 June 2019 - 558 words (3 minutes)

It’s a commonly held belief that we need to eat at least 120 grams of carbohydrate per day in order to provide glucose to our brains.  

This, however, is a myth! 

It is true that if we are eating carbohydrates, the brain is going to use the glucose produced for fuel.  And it is true that the blood stream contains a small amount of glucose – about 5 grams, equivalent to about a teaspoon.  It is not true, however, that the brain can only use glucose for fuel. And it is not true that dietary carbohydrates are required to provide this glucose to the brain! 

The liver and gluconeogenesis 

Your liver is an amazing factory... And it can make glucose! Even in the total absence of dietary carbohydrate, the body can make all the glucose it needs. 

Gluconeogenesis is the conversation of ‘non-glucose substrates’ (like fat, protein or lactate) into glucose, providing any glucose necessary for the brain or the body[1]. This is why there is no “essential” carbohydrate, unlike “essential” amino acids (to build proteins), and “essential” fatty acids (to build fats), which are required in the diet, since your body can’t make them. Without essential amino acids or fatty acids, a person will eventually become deficient, and may even die. However, without a single gram of carbohydrate, there is no ill effect whatsoever – since the liver can make glucose. 

The brain and ketones 

A by-product of the breakdown of fat in the liver is ketones. When blood ketone levels reach about 0.5mmol/L, ketones can cross the blood brain barrier, becoming the preferred fuel for the brain[2][3]. This level of ketones (and higher) is likely to be present in anyone following a low-carbohydrate, high (healthy) fat diet.  

Ketones: the optimal human fuel  

In hunter-gatherer times, ketones would have been our brain’s primary fuel source.  

The invention of agriculture about 10,000 years ago meant that humans, for the first time, had a reliable and constant source of food – mostly from carbohydrate-based crops. Prior to this, our eating pattern had been generally lower in carbohydrates, and interspersed with periods of fasting (due to food shortages)[4].  

The human body can only store enough glycogen (the storage form of glucose) to last about 24 hours. Between low-carb dietary patterns and intermittent fasting, our hunter-gatherer ancestors would have regularly relied on ketones to fuel their brains and their bodies[5]. Without ketones, brain function would have been rapidly compromised whenever food was scarce - and we would have had to break down huge amounts of lean muscle mass in order to provide continuous glucose to the body. Ketones – a reliable, abundant and clean source of energy for the human body and brain – ensured our survival[6]. 

In fact, without ketones, our brains would never have developed to be as large as they are today. During pregnancy, ketones are essential in meeting the foetuses’ energy requirements[7]. Ketones are the preferred source for the synthesis of brain lipids – and of all the mammals, human babies are born with the largest reserves of fat – a ready supply of ketones to build the human brain[8].

Ketones: beyond just a fuel 

The brain can not only use ketones as fuel – ongoing research is uncovering the huge range of unique benefits that ketones have to cognitive health[9]. For example, ketones appear to have a neuroprotective effect on brain cells – improving metabolic efficiency and lowering the production of reactive oxygen species, protecting the brain from oxidative stress[10]. Ketones actually produce more energy for the body (in the form of ATP) than glucose does, with fewer damaging by-products[11].

Ketones are being used in the treatment of Alzheimer’s dementia – because in Alzheimer’s, the brain cells are unable to metabolise glucose effectively, but can still use ketones[12]. Supplementation or dietary changes to promote ketosis have been shown to improve cognition in patients with Alzheimer’s disease, traumatic brain injury, and memory impairment[13].

Ketogenic diets and fasting are well known for their ability to ‘calm’ the brain, preventing epileptic seizures[14], and are being investigated as therapeutic adjuvants (substances which enhance the body's immune response) for Parkinson’s disease[15]. Growing evidence suggests that ketosis enhances cognition, memory and learning[16][17].  

So, no, you don’t need dietary carbohydrate for your brain (or your body). And at The Low Carb Clinic, we can help you to formulate a diet that allows your brain and body to run on an efficient and beneficial fuel source – ketones.  

References 

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1. Owen, O., Morgan, H., Kemp, G., Sullivan, M., Herrera, M., & Cahill, G. (1967). Brain metabolism during fasting. The Journal of Clinical Investigation, 46(10), 1589-1595. 
2. Volek, J., Freidenreich, D., Saenz, C., Kunces, L., Creighton, B., Bartley, J., . . . Phinney, S. (2016). Metabolic characteristics of keto-adapted ulta endurance runners. Metabolism, 65, 100-110. doi:http://dx.doi.org/10.1016/j.metabol.2015.10.028 
3. LaManna, J., Salem, N., & Puchowicz, M. (2009). Ketones suppress brain glucose consumption. Advanced Experimental Medicine and Biology, 645, 301-306. doi:10.1007/978-0-387-85998-9_45 
4. Fine, E., Champ, C., Feinman, R., Marquez, S., & Klement, R. (2016). An evolutionary and mechanistic perspective on dietary carbohydrate restriction in cancer prevention. Journal of evolution and health, 1(1). doi:https://doi.org/10.15310/2334-3591.1036 
5. Fine, E., Champ, C., Feinman, R., Marquez, S., & Klement, R. (2016). An evolutionary and mechanistic perspective on dietary carbohydrate restriction in cancer prevention. Journal of evolution and health, 1(1). doi:https://doi.org/10.15310/2334-3591.1036 
6. Fine, E., Champ, C., Feinman, R., Marquez, S., & Klement, R. (2016). An evolutionary and mechanistic perspective on dietary carbohydrate restriction in cancer prevention. Journal of evolution and health, 1(1). doi:https://doi.org/10.15310/2334-3591.1036 
7. Cunnane, S., & Crawford, M. (2003). Survival of the fattest: fat babies were the key to evolution of the large human brain. Comparative Biochemistry and Physiology, 136, 17-26. doi:10.1016/S1095-6433(03)00048-5 
8. Cunnane, S., & Crawford, M. (2003). Survival of the fattest: fat babies were the key to evolution of the large human brain. Comparative Biochemistry and Physiology, 136, 17-26. doi:10.1016/S1095-6433(03)00048-5 
9. Hallbook, T., Ji, S., Maudsley, S., & Martin, B. (2011). The effects of the ketogenic diet on behaviour and cognition. Epilepsy Research, 100(3), 304-309. doi:10.1016/j.eplepsyres.2011.04.017 
10. Hallbook, T., Ji, S., Maudsley, S., & Martin, B. (2011). The effects of the ketogenic diet on behaviour and cognition. Epilepsy Research, 100(3), 304-309. doi:10.1016/j.eplepsyres.2011.04.017 
11. Manninen, A. (2004). Metabolic effects of the very-low-carbohydrate diets: misunderstood "villains" of human metabolism. Jounral of the International Society of Sports Nutrition, 1(2), 7-11. doi:10.1186/1550-2783-1-2-7 
12. Lange, K., Lange, K., Makulska-Gertruda, E., Nakamura, Y., Reissmann, A., Kanaya, S., & Hauser, J. (2016). Ketogenic diets and Alzheimer's disease. Food Science and Human Wellness, 6(1). doi:https://doi.org/10.1016/j.fshw.2016.10.003 
13. Reger, M., Henderson, S., Hale, C., Cholerton, B., Baker, L., & Watson, G. (2004). Effects of beta-hydroxybutyrate on cognition in memory-impaired adults. Neurobiology of Aging, 25(3), 311-314. doi:10.1016/S0197-4580(03)00087-3 
14. Gasior, M., Rogawski, M., & Hartman, A. (2006). Neuroprotective and disease-modifying effects of a ketogenic diet. Behavioural Pharmacology, 17(5), 431-439. 
15. Anton, S., Moehl, K., Donahoo, W., Marosi, K., Lee, S., Mainous, A., . . . Mattson, M. (2018). Flipping the metabolic switch: understanding and applying health benefits of fasting. Obesity, 26(2), 254-268. doi:10.1002/oby.22065 
16. Hallbook, T., Ji, S., Maudsley, S., & Martin, B. (2011). The effects of the ketogenic diet on behaviour and cognition. Epilepsy Research, 100(3), 304-309. doi:10.1016/j.eplepsyres.2011.04.017 
17. Reger, M., Henderson, S., Hale, C., Cholerton, B., Baker, L., & Watson, G. (2004). Effects of beta-hydroxybutyrate on cognition in memory-impaired adults. Neurobiology of Aging, 25(3), 311-314. doi:10.1016/S0197-4580(03)00087-3