Ketones and Brain Health: How Ketones Fuel Your Brain
Your brain doesn’t run on glucose alone. It can also use ketones, an alternative fuel made by the liver from fat. Think of it a little like a hybrid car, able to draw on more than one source of energy.
Most of the time, your brain relies heavily on glucose. But when ketones are available, it can use these alongside glucose to help meet its considerable energy demands. Brain cells can use other fuels too, including lactate, but glucose and ketones are our focus here.
This ability to use different fuels is one reason ketones have become such an interesting area of brain research, particularly as we age. So what does science actually tell us about ketones and brain health? And can you raise your ketones without following a strict ketogenic diet?
Ketones and brain health: quick answers:
Are ketones good for the brain? Your brain prefers glucose but it can also use ketones, made in the liver during fasting, carbohydrate restriction or a ketogenic diet. As we age, and especially in the early stages of Alzheimer’s, the brain often gets worse at using glucose while its ability to use ketones holds up. That’s why researchers are investigating ketones as a way to support brain energy.
Is ketogenic diet good for brain health? Ketogenic diets have an established medical role in some forms of epilepsy. Early trials in mild cognitive impairment and Alzheimer’s disease are encouraging, but the evidence isn’t yet strong enough to say everyone should follow a strict ketogenic diet for better brain health.
What are ketones?
Ketones are an alternative source of energy for the brain, produced mainly by the liver when carbohydrate availability is low. Ketones, or ketone bodies, are small, fast fuel molecules that your liver makes from fat when glucose is in short supply. The two that matter for energy are beta-hydroxybutyrate (BHB) and acetoacetate. A third, acetone, is the one you breathe out, which is where “keto breath” comes from.
Brain cells, or neurons, are tightly packed and need instant fuel. They can’t burn fatty acids the way muscle cells can, so they rely on just two fuels: glucose or ketones. Support cells called astrocytes sit right next to the neurons and help supply them with fuel.[9]
You make some ketones every night while you sleep. Levels rise further the longer you go without food, the fewer carbohydrates you eat, and when you eat certain fats, especially the medium-chain fats in C8 oil.
Can your brain run on ketones?
Yes, to a large degree, though never completely.
On a typical carb-rich diet, glucose supplies around 90–95% of the brain’s energy and ketones only about 5–10%.[10] Much of the time the brain simply isn’t offered many ketones.
That changes when carbohydrates are scarce. In the classic study on this question, three people fasted for five to six weeks under medical supervision. By the end, ketones had overtaken glucose as their brain’s main fuel, supplying roughly two-thirds of its energy.[6] That’s an extreme situation, but it shows how much ketone fuel the brain can handle.
A few points follow from this:
The brain still needs some glucose. You don’t need to eat it, though. Your liver makes what’s required from protein and from the glycerol part of fat.
The more ketones in your blood, the more your brain uses. Cunnane’s team has shown that brain ketone uptake rises in step with blood ketone levels. This holds in people with Alzheimer’s just as it does in healthy young adults.[9,12]
Does the brain prefer ketones?
Patrick Holford, founder of Food for the Brain, argues in his book on Alzheimer’s prevention that when ketones are available, the brain will use them in preference, especially in people with age-related memory decline. It’s a view shared by many researchers in the field, though it isn’t fully settled. What is clear is that the brain uses ketones readily whenever they’re there.
Although it makes up only about 2% of body weight, the brain uses around 20% of the body’s energy.[11] For such a demanding organ, having a second fuel is a real advantage.
Ketones, Brain Energy and the Ageing Brain
What is the brain energy gap?
Having enough glucose in your blood doesn’t necessarily mean every part of your brain is using it well. Studies have found reduced glucose use in some brain regions in mild cognitive impairment and Alzheimer’s disease.
Why does this happen? There isn’t one simple answer. Metabolic health and insulin signalling may play a part, but it would be misleading to say that insulin resistance simply shuts glucose out of brain cells.
Could ketones help fill that energy gap?
That’s what researchers are testing.
Too much sugar, and particularly the fruit sugar fructose (half of table sugar and most of the high-fructose corn syrup in fizzy drinks and ultra-processed foods), drives insulin resistance. Insulin is the hormone that helps deliver glucose into brain cells. So the ironic end result of constantly eating too much sugar is glucose starvation in the brain.[16,17] That’s when you feel brain fog, struggle to concentrate and crave more sugar. Cunnane sums it up on one of his slides: more dietary sugar means less brain sugar.[10]
His brain-scanning research shows this is part of the Alzheimer’s story. In people with Alzheimer’s and Parkinson’s, the brain’s glucose uptake falls by around 15–30%.[10] In one study of mild Alzheimer’s, glucose uptake was about 13% lower than in healthy people of the same age, while ketone uptake was no different.[7] The problem is that the ketone supply doesn’t rise to make up the shortfall. The result is an energy gap, and it can appear in certain brain regions before any symptoms do.[9]
“People with cognitive decline have an energy gap. Probably due to insulin resistance, they are not able to make use of glucose. Providing a food source, C8 oil, from which the body can readily make ketones, fills that energy gap, brain cells come back to life and memory and brain function improve as a result. It reminds me of those announcements on the London Underground: ‘Mind the gap.'” Professor Stephen Cunnane, University of Sherbrooke, speaking to Patrick Holford for his book on Alzheimer’s prevention
Cunnane is a member of our Scientific Advisory Board and holds the Clinical Research Chair in Ketotherapeutics at the University of Sherbrooke in Canada. He is an expert on fatty acid metabolism in the brain.
Ketones, memory and Alzheimer’s disease
If the ketone supply line still works, can topping it up help? What happens when researchers put this idea to the test? Here are three examples, looking at brain energy, memory and everyday function.
Brain energy. Cunnane’s team gave people with mild to moderate Alzheimer’s 30g a day of ketogenic MCT oil for a month. Their brain’s ketone uptake roughly doubled, while its use of glucose stayed the same, so the brain’s total energy supply went up.[12]
Memory and thinking. In a six-month randomised controlled trial led by Dr Melanie Fortier and Cunnane, 122 people with mild cognitive impairment took either a ketogenic MCT drink (15g twice a day) or a placebo.[8] The MCT group did better than the placebo group on tests of memory, verbal fluency, naming and attention/processing, and the bigger their rise in brain ketones, the bigger the improvement. The study enrolled 122 people, and 83 completed it. Some cognitive test results improved compared with placebo, but the dropouts matter when judging how practical and reliable the approach may be.
Diet. In New Zealand, 26 people with Alzheimer’s followed a modified ketogenic diet and a healthy low-fat diet, each for 12 weeks. Of those, 21 completed both.[13] On the ketogenic diet, their ability to manage daily activities and their quality of life both improved, which is striking at that stage of the disease. Cognitive scores also went up, but not by enough to be statistically significant.
These are small or early trials, and quite a few participants dropped out, mainly because of digestive side effects from the MCT oil. Together they suggest that ketones can help support a brain that’s struggling with energy. They don’t show that ketones prevent or reverse Alzheimer’s.
That’s why we see ketones as one part of a bigger prevention picture. Disturbed glucose balance is one of “four biological horsemen” that together drive risk, alongside low omega-3, low B vitamins (shown by raised homocysteine) and low antioxidants. Activity, sleep, stress and social connection matter too. Even for people who carry the ApoE4 gene variant, eating a low-GL or more ketogenic Mediterranean-style diet could help.[14]
Is a keto diet good for brain health?
A ketogenic diet is very low in carbohydrate and high in fat, strict enough to keep the body making ketones continuously. Beyond Alzheimer’s, there are three other areas of evidence for the brain.
Epilepsy. The ketogenic diet has been used under specialist medical supervision for drug-resistant epilepsy since the 1920s, in both children and adults. For some people it markedly reduces how often seizures happen.[1] This is the most established medical use of the diet, and it’s always done with a specialist team.
Parkinson’s disease. In a small eight-week trial, 38 people with Parkinson’s completed either a low-fat or a ketogenic diet.[2] Both groups improved to a similar degree on motor symptoms such as tremor and stiffness. The keto group, however, improved far more on non-motor symptoms: 41% compared with 11%. These included fatigue, daytime sleepiness, pain, urinary problems and cognitive symptoms.
Fatigue and mood. It has been proposed that ketones could help in chronic fatigue syndrome, through the same energy-supply logic.[3] Low-carb, ketogenic diets are also being studied in mental health conditions. Both are early-stage areas.
So is keto good for your brain? Honestly, it depends on the health issues are facing. For most people, they can get the benefits of ketones without living on a strict ketogenic diet. Either through ketone supplementation or by having a ‘hybrid diet’ where you have periods of time eating in a ketogenic way (outlined in one of Patrick’s books the Hybrid Diet)
How to Increase Ketones Naturally
Your body makes more ketones when carbohydrate availability falls. Fasting, a ketogenic diet and MCT oil can all increase ketone availability, but they work differently. Raising ketones is one thing. Showing a benefit for brain health is another.
1. Cut back on sugar and refined carbs.
Every time you eat sugar or starchy carbs, insulin rises and ketone production switches off. Food for the Brain’s Alzheimer’s prevention advice is simple:
- Avoid “the white stuff”: sugar, white flour and white rice.
Cunnane’s team found that cutting carbohydrate intake by 30% in a retirement home for two months lowered blood sugar by 11% and increased ketones.[10]
2. Stretch your overnight fast.
It takes only about 12 hours to start running low on stored glucose and begin switching towards ketones. An 18:6 pattern goes further: you don’t eat between dinner at 6 or 7pm and lunch at 12 or 1pm the next day. Holford recommends doing this a couple of days a week, with a Hybrid Latté in the morning (see below). “My brain stays sharp and I don’t feel hungry,” he says.
3. Go ketogenic for a while.
To tip into ketosis you need to keep carbohydrates very low but our founder Patrick Holford suggests going ketogenic for about a week, or once a month, as a “service” for your brain rather than as a permanent diet.
4. Add C8 oil
This is the shortcut that doesn’t need a strict diet, and it’s covered below.
5. Keep moving.
Cunnane lists moderate, regular exercise alongside ketones as one of his strategies to fuel and protect the brain.[10] Exercise uses up stored glucose, so it nudges the body towards burning fat.
6. Coffee helps too
Coffee gives you energy the way a bank loan gives you wealth, but it does speed up the switch to running on ketones.[5]
If you want to check it’s working, you can measure blood, breath or urine ketones with a home meter. As a rough guide, a blood BHB reading of 0.5 mmol/L or above is usually described as nutritional ketosis. It’s also worth knowing your HbA1c, a blood test that shows your average blood sugar over the past few months. The FFB Alzheimer’s prevention advice is to aim for below 5.4% (36 mmol/mol), and ideally around 5%.
Can MCT oil increase ketones?
Yes. Certain medium-chain fats, particularly C8, can raise blood ketones without the same degree of carbohydrate restriction as a strict ketogenic diet. But the amount, formulation and individual response matter. Medium-chain triglycerides (MCTs) have chains of 6 to 12 carbons (C6, C8, C10 and C12). Unlike most fats, they go straight to the liver, where they are turned into ketones quickly. Of these, C8 (caprylic acid triglyceride, also called tricaprylin) makes ketones the fastest. In a study by Cunnane’s group, C8 raised blood ketones more than C10, other MCTs or coconut oil. C10 came next, but it’s not nearly as effective.[4]
Coconut oil vs C8 oil
This is where a lot of people get caught out. Coconut oil is around 60% MCTs, but only about 12% of those MCTs are C8, so only about 7% of coconut oil is C8. Most of the rest is C12 (lauric acid), which behaves more like an ordinary long-chain fat.
That’s why bulletproof coffee, with a blob of coconut oil or MCT oil in your morning brew, is one way to raise ketones but is much less effective than pure C8 oil. Patrick Holford’s Hybrid Latté is a step up. It’s a coffee made with carb-free almond milk, almond butter, C8 oil, a teaspoon of unsweetened cacao and half a teaspoon of cinnamon.
How to take C8 oil. In Cunnane’s studies, people took about two tablespoons (30g) a day.[8,12] The energy effect lasts a few hours, so it’s best spread across the day. Food for the Brain suggests starting with a teaspoon two or three times a day and building up gradually to two teaspoons three times a day. It has a pleasant, creamy taste. Some people get digestive upset. You can minimise this by building up slowly, taking it with a meal, or blending it into a smoothie or coffee so it’s emulsified.
Do foods contain ketones?
Not in any meaningful amount. Ketone bodies are made inside your body, so you don’t get them from food the way you get vitamins. This is a common point of confusion.
Two things cause the mix-up:
“Keto foods” help you make ketones; they don’t contain them. These are mainly fats and oils, especially C8 oil and, to a lesser extent, coconut oil, eaten with very little carbohydrate.
“Raspberry ketone” is not a ketone body. It’s an aroma compound that belongs to the same broad chemical family. It isn’t BHB or acetoacetate, and it doesn’t fuel your brain in the same way.
So if you want more ketones from what you eat, three things matter: what you leave out (sugar and refined carbs), when you eat (longer gaps), and one specific addition (C8 oil).
Are ketones or a ketogenic diet safe?
For most people, raising ketones with a longer overnight fast or some C8 oil is well tolerated.
A few things are worth knowing:
- Early “keto flu”. When people first cut or reduce carbohydrates hard, some feel tired, headachy or foggy for a few days while their body adapts. It usually passes, and many people then report clearer thinking and steadier energy.
- Digestive upset from MCT oil. This is the most common side effect, and it’s why building up slowly matters. Start with ½ tsp and slowly build up over time.
- Check with your GP first before fasting or starting a ketogenic diet if you take medication for diabetes or blood pressure, are pregnant or breastfeeding, have a history of disordered eating, or have liver, kidney or pancreatic problems.
The bottom line
Your brain has more than one source of fuel. Ketones are an important part of that picture, and research in people with cognitive impairment is encouraging. But we still need to know who benefits, which approach works best and whether any benefits last.
You don’t need to chase a ketone reading to start looking after your brain. Our free Cognitive Function Test and accompanying questionnaire can help you explore your cognitive performance and the diet and lifestyle factors that may deserve attention.
To see what’s happening in your body, the DRIfT® home blood test measures five key biomarkers, including HbA1c for blood sugar balance.
References
- Owen OE, Morgan AP, Kemp HG, Sullivan JM, Herrera MG, Cahill GF Jr. Brain metabolism during fasting. Journal of Clinical Investigation. 1967;46(10):1589–1595. doi:10.1172/JCI105650.
- Cunnane SC. Ketones: an essential brain fuel to support cognitive function during aging. Presentation at Food for the Brain’s Alzheimer’s Prevention: New Frontiers conference; 28 April 2026.
- Raichle ME, Gusnard DA. Appraising the brain’s energy budget. Proceedings of the National Academy of Sciences of the United States of America. 2002;99(16):10237–10239. doi:10.1073/pnas.172399499.
This article is for information only and is not medical advice. It does not replace consultation with a qualified healthcare professional. Please speak to your GP before making significant changes to your diet, fasting or starting supplements, especially if you have a medical condition or take medication.
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