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Is Fat the Best Brain Fuel?

Watch this film – fuel your brain with fat or slow carbs for better energy

All cells in the body can burn either sugar for energy, or fatty acids, derived from fat. That fat can come from fat you’ve eaten or your own fat if you go on a low-calorie diet. However, brain cells, called neurons, cannot. There are so many neurons – some 100 billion of them – packed into such a small area that there isn’t any free space, so they have to use the cleanest, fastest, most efficient fuel, rather than inefficient fat. Usually this is glucose, but when the glucose ‘engine’ starts to malfunction, as often happens with diabetics and those with memory decline, ketones, made in the liver from fat, are a terrific alternative source of energy for the brain. Ketones are actually used to build babies’ brains.

Babies are born with 50 trillion brain connections and need to make up to a million a second in the first few months, with the brain consuming 75% of all energy from food! The only way a baby’s brain can get all the energy it needs for rapid building is from ketones. There’s just a limit to how much glucose the brain can use. That’s why human breast milk is relatively high in fat and babies are born fat. The liver can make ketones from body fat.

You don’t have to generate ketones for the brain to work optimally even though it might help. Normally, the brain is using about 22% of the total energy we take in. You can get all that from glucose. However, if there are ketones in your system the brain will selectively use this in preference, suggesting that neurons like running on ketones. 

Ketones are only made in the liver from certain kinds of fat called Medium-Chain Triglycerides (MCTs). Fats are made of a chain of carbon atoms. An MCT is between 6 and 12 carbon atoms long. Coconut, palm and olive oil are sources of MCTs. However, recent research has proven that almost all ketones are made from a sub-fraction of these fats called C8 (short for carbon 8, or caprylic acid triglyceride, an 8 carbon chain fat).[i] Coconut oil is only 7% C8 while MCT oil, which you can buy in the health food store, is 12% C8. You’re better off getting pure C8 oil, which is also available in health food stores and online, if you want to supply your brain with ketones.

Two breakthrough studies in Canada, by Dr Melanie Fortier and Professor Stephen Cunnane from Sherbrooke University in Canada have established that C8 oil can be extremely helpful as an energy source for those with cognitive decline. Cunnane is an expert on fatty acid metabolism in the brain who has held the ‘Canada Research Chair on Dietary Fatty Acids and Cognitive Function during Ageing’.

They ran two studies, giving people with either Alzheimer’s[i] or pre-dementia[ii], called mild cognitive impairment (MCI), two tablespoons of C8 oil (30g) or placebo and measured their cognitive abilities, as well as how much energy their brains made. They kept making the same amount of energy from glucose but, in addition, had a 230% increase in energy made from ketones. In those with pre-dementia they found that ‘Measures of episodic memory, language, executive function, and processing speed improved on the C8 versus baseline. Increased brain ketone uptake was positively related to several cognitive measures.’

Another good example of ketone power is the work of Kieran Clarke, Professor of Physiological Biochemistry at Oxford University. Having been approached by the American Defense Advanced Research Projects Agency (DARPA) she had the opportunity to test ketones as an energy source in combat situations. “They were looking for an energy source that would improve soldiers’ mental and physical performance under battlefield conditions,” she says. “Troops weren’t taking enough rations into action because they filled their rucksacks with extra ammunition instead. As their blood glucose dropped, they became confused, sometimes ended up shooting their own side.”

She had synthesised ketones, and tried them out on the soldiers. “We called it DeltaG which is the biochemical name for energy but also has a military ring to it – Delta Force and all.” She tried the new compound on rats a few years later and found it boosted their physical and mental performance. Those who got 30% of their diet in the form of ketones ran 30% further on a treadmill and were smarter at finding their way out of a maze. Most professional endurance athletes supplement pure ketones when they need a boost.

Ketones help Parkinson’s disease

In light of the profound effect that the ketogenic diet has on the structure and workings of the brain, it is plausible to suggest that it might prove useful in the treatment of Parkinson’s disease. All of the studies in this area are still in their early stages, but some of the initial results are promising.

Parkinson’s patients have insufficient amounts of the neurotransmitter dopamine, and at present they are routinely treated with an amino acid named L-dopa. However, for it to work, the neurons’ mitochondria need to be able to generate sufficient energy to turn it into dopamine. As we know, the mitochondria are usually powered by glucose that is extracted from carbohydrates, but if this process isn’t working well – and there is evidence that this is often the case among Parkinson’s patients – the ketones produced during ketosis could be extremely beneficial.

One trial placed one group of patients on a low fat, high carb diet and another group on a ketogenic diet for a period of eight weeks.[1] Those on the latter diet showed a 41% reduction in shaking, as well as improvements in behaviour and mood, compared with only an 11% improvement among those on the low fat diet. The high carb group also experiencedmore hunger.

Parkinson’s experts Geoffrey and Lucille Leader point out that certain amino acids compete for absorption with the standard medication for the condition, so some protein-rich foods should not be eaten within two hours of taking the medication. (The Leaders explain their approach in detail in their book Parkinson’s Disease: Reducing Symptoms with Nutrition and Drugs.[2]) Therefore, supplementing exogenous ketones either alongside or shortly after medication, while avoiding protein-rich foods, certainly seems to merit a trial.

A High Fat Ketogenic Diet Can Counteract Epilepsy

The ketogenic diet has long been a standard treatment for childhood epilepsy. Indeed, the benefits of this approach have been well known for about a hundred years.[3] However, it was 2008 before Professor Helen Cross, a neurologist and expert in childhood epilepsy at Great Ormond Street Hospital, London, ran the first rigorous scientific trial. Unsurprisingly, this proved what many neurologists had known all along: that a high fat diet is a highly effective treatment for epilepsy. [4]

Another more recent trial found similar results with twice as many patients in the ketogenic diet group having a significant decrease in seizure severity.[5]

‘About 30% of epileptic children don’t respond to the drugs and they can have a dreadful time: a hundred fits a day is not uncommon,’ says Susan Wood, a registered dietitian who works for Matthew’s Friends Clinics, a registered charity that advocates the introduction of the ketogenic diet for all sufferers of the condition. It’s still not exactly clear why this diet is so effective, but it probably has something to do with reducing the activity of one of the excitatory chemicals in the brain (glutamate) while promoting the production of GABA, an inhibitory neurotransmitter which calms down adrenal responses, as well as being a fuel source for neurons.[6] Simply reducing carbs also seems to have an anti-seizure effect, while changes in the neurons’ mitochondria, the energy factories, may be involved, too. Moreover, a recent study in  The Lancet found that MCT oil (which is often taken as part of the diet) has some significant direct effects, such as blocking glutamate receptors and increasing the amount of energy that is available to neurons by boosting their mitochondria.[7]

Is Alzheimer’s Brain Diabetes?

One recent theory suggests that Alzheimer’s should be considered as a form of diabetes of the brain, so, like diabetes itself, treatment should focus on reducing the body’s levels of insulin and glucose. This makes sense, as diabetics are three times more likely to develop Alzheimer’s than non-diabetics.

Stephen Cunnane explains, ‘The brain has the greatest demand for fuel of any organ in the body and evolutionarily ketones emerged to ensure that the brain’s rapacious demand had a greater chance of being met. This source of fuel may also have been a factor allowing for the threefold expansion of the brain around two million years ago that is associated with all our highly developed cognitive abilities.’ Cunnane adds that ketones are still vital for wiring up the human brain during infancy: ‘They are produced from MCTs [medium-chain triglycerides] in mothers’ milk, and even when babies stop breastfeeding, they remain in ketosis at much higher levels than adults for the first year of their lives.’[8] Indeed, it is estimated that ketones meet half of the energy needs of an infant’s brain, precisely at the time when the organ is expanding at a furious rate and demanding massive amounts of fuel.

Babies can survive on the ketones that their livers produce from their own fat reserves for as long as sixty days; and, interestingly, even a high carb diet doesn’t push them out of ketosis. Given this preference for ketones during construction of the brain at the beginning of life, it makes sense that the same fuel is equally beneficial towards the end, especially in those areas of the brain that are involved in memory and cognition.

Professor Cunnane’s research has shown that Alzheimer’s patients start to suffer glucose deficiency in certain regions of the brain even before they start to experience any symptoms. There may be various reasons for this, including low grade infections, which increase the immune system’s demands for glucose, and insulin resistance, which makes it more difficult for the fuel to make its way into the neurons. ‘We know from our scanning research that the glucose deficit is not due to damage to the neurons, but to insufficient amounts being available as fuel,’ explains Cunnane. ‘It’s safe to treat this deficiency with ketones.’ On the other hand, if the condition remains untreated, the fuel-deprived neurons suffer the sort of damage that ultimately leads to Alzheimer’s.

If you’d like to experiment with a lower carb, higher fat ketogenic diet The Hybrid Diet by Jerome Burne and Patrick Holford, explains how to do this safely.

Food for the Brain is a non-for-profit educational and research charity that offers a free Cognitive Function Test and assesses your Dementia Risk Index to be able to advise you on how to dementia-proof your diet and lifestyle.

By completing the Cognitive Function Test you are joining our grassroots research initiative to find out what really works for preventing cognitive decline. We share our ongoing research results with you to help you make brain-friendly choices.

Please support our research by becoming a Friend of Food for the Brain.


[1] Vandenberghe C, St-Pierre V, Pierotti T, Fortier M, Castellano CA, Cunnane SC. Tricaprylin Alone Increases Plasma Ketone Response More Than Coconut Oil or Other Medium-Chain Triglycerides: An Acute Crossover Study in Healthy Adults. Curr Dev Nutr. 2017 Mar 22;1(4):e000257. doi: 10.3945/cdn.116.000257. PMID: 29955698; PMCID: PMC5998344.

[2] Croteau E, Castellano CA, Richard MA, Fortier M, Nugent S, Lepage M, Duchesne S, Whittingstall K, Turcotte ÉE, Bocti C, Fülöp T, Cunnane SC. Ketogenic Medium Chain Triglycerides Increase Brain Energy Metabolism in Alzheimer’s Disease. J Alzheimers Dis. 2018;64(2):551-561. doi: 10.3233/JAD-180202. PMID: 29914035.

[3] Fortier M, Castellano CA, St-Pierre V, Myette-Côté É, Langlois F, Roy M, Morin MC, Bocti C, Fulop T, Godin JP, Delannoy C, Cuenoud B, Cunnane SC. A ketogenic drink improves cognition in mild cognitive impairment: Results of a 6-month RCT. Alzheimers Dement. 2021 Mar;17(3):543-552. doi: 10.1002/alz.12206. Epub 2020 Oct 26. PMID: 33103819; PMCID: PMC8048678.

[4] M. Phillips et al., ‘Low-fat versus ketogenic diet in Parkinson’s disease: a pilot

randomized controlled trial.’ Movement Disorders (2018),

[5] Geoffrey Leader and Lucille Leader, Parkinson’s Disease: Reducing Symptoms with Nutrition and Drugs, 3rd edn, London: Denor Press, 2017.

[6] R.M. Wilder, ‘The effect of ketonemia on the course of epilepsy’, Mayo Clinic Proceedings (1921), vol 2:307–308.

[7] Neal EG, Chaffe H, Schwartz RH, Lawson MS, Edwards N, Fitzsimmons G, Whitney A, Cross JH. The ketogenic diet for the treatment of childhood epilepsy: a randomised controlled trial. Lancet Neurol. 2008 Jun;7(6):500-6. doi: 10.1016/S1474-4422(08)70092-9. Epub 2008 May 2. PMID: 18456557.

[8] Lambrechts DA, de Kinderen RJ, Vles JS, de Louw AJ, Aldenkamp AP, Majoie HJ. A randomized controlled trial of the ketogenic diet in refractory childhood epilepsy. Acta Neurol Scand. 2017 Feb;135(2):231-239. doi: 10.1111/ane.12592. Epub 2016 Mar 29. PMID: 27027847.

[9] Jensen NJ, Wodschow HZ, Nilsson M, Rungby J. Effects of Ketone Bodies on Brain Metabolism and Function in Neurodegenerative Diseases. Int J Mol Sci. 2020 Nov 20;21(22):8767. doi: 10.3390/ijms21228767. PMID: 33233502; PMCID: PMC7699472; see also Brietzke E, Mansur RB, Subramaniapillai M, Balanzá-Martínez V, Vinberg M, González-Pinto A, Rosenblat JD, Ho R, McIntyre RS. Ketogenic diet as a metabolic therapy for mood disorders: Evidence and developments. Neurosci Biobehav Rev. 2018 Nov;94:11-16. doi: 10.1016/j.neubiorev.2018.07.020. Epub 2018 Jul 31. PMID: 30075165.

[10] K. Augustin et al., ‘Mechanisms of action for the medium-chain triglyceride

ketogenic diet in neurological and metabolic disorders’, Lancet Neurology (2018), vol 17(1):84–93.

[11] P.F. Bougneres et al., ‘Ketone body transport in the human neonate and infant’, Journal of Clinical Investigation (1986), vol 77(1):42–48.