Does Keto Make You Smarter? What the Research Shows for IQ
Does keto make you smarter? No trial has measured IQ. In healthy adults, keto diets left test scores unchanged; small trials in memory loss show modest gains.
Dr. Russell T. WarneChief Scientist
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There is no evidence that a ketogenic (keto) diet makes healthy people smarter: no trial has measured IQ, and controlled trials in healthy adults found no change in cognitive test scores. The positive findings come from small trials in older adults with mild cognitive impairment or Alzheimer's disease, where a 2026 meta-analysis of 12 trials found a modest gain on cognitive tests (a standardized difference of 0.34).
A ketogenic diet cuts carbohydrate so sharply that the liver starts turning fat into "ketones", which the brain can burn in place of glucose. Our page on fasting and IQ explains that switch in more detail. This page covers what the keto trials found in healthy adults, in people with memory loss and in children with epilepsy, what ketone drinks add, and why the "keto brain fog" people describe early on is a real but temporary complaint. It describes research and is not medical or dietary advice.
Where the keto brain claim comes from
The ketogenic diet began as a medical treatment. Doctors have used it since the 1920s for children whose epileptic seizures do not respond to drugs, and a randomized trial by Neal and colleagues in 145 children confirmed that it reduces seizures. That medical history is covered on our page on epilepsy and IQ.
The newer claim, popular in diet books and online, is that ketones are a "cleaner" brain fuel that sharpens focus in anyone. The scientific starting point is narrower. In a PET imaging study by Castellano and colleagues, people with mild Alzheimer's disease took up about 13% less glucose in grey matter than healthy people of the same age, but their brains used ketones normally. So researchers have asked whether ketones can fill an energy gap in an aging or damaged brain. Whether a healthy brain, which already has enough fuel, benefits from the switch is a separate question.
What keto trials show in healthy adults
Healthy adults are the group most people mean when they ask whether keto makes you smarter, and they have been studied the least. The trials that exist found no cognitive benefit.
• Three weeks in healthy young adults: Iacovides and colleagues put 11 healthy, normal-weight adults on a ketogenic diet and a high-carbohydrate diet with the same calories, in random order, for at least three weeks each. Blood tests confirmed ketosis. Vigilance, visual learning and memory, working memory and executive function did not differ between the diets, and neither did mood or sleep.
• One year in adults with obesity: Brinkworth and colleagues randomized 106 overweight and obese adults to a very low-carbohydrate, high-fat diet or a low-fat diet for a year. Both groups lost similar weight. Working memory improved over the year in both groups and processing speed barely changed, with no difference between diets. Mood improved more on the low-fat diet.
• One year in type 2 diabetes: Tay and colleagues randomized 115 adults with obesity and type 2 diabetes to a very low-carbohydrate or a high-carbohydrate diet, both with supervised exercise, for 52 weeks. On tests of reasoning ability, reasoning speed, working memory, verbal fluency, processing speed and memory, the two diets had the same effect.
The first trial was tiny, and the two larger ones tested low-carbohydrate diets in adults with obesity rather than in lean people. Together they suggest that cutting carbohydrate neither helps nor harms test performance much in adults without a brain disorder.
Keto, memory loss and Alzheimer's disease
The case for keto as a cognitive treatment rests on trials in older adults whose memory is already declining.
• Mild cognitive impairment: Krikorian and colleagues randomized 23 older adults with mild cognitive impairment to a very low-carbohydrate or a high-carbohydrate diet for six weeks. Verbal memory improved in the low-carbohydrate group, and higher ketone levels went with better memory scores. The study was funded by the Robert C. and Veronica Atkins Foundation and the National Institute on Aging.
• A modified Mediterranean keto diet: Neth and colleagues gave 20 older adults with memory complaints or mild cognitive impairment a modified Mediterranean-ketogenic diet and a standard heart-healthy diet, six weeks each. Alzheimer's markers in spinal fluid improved on the keto diet, but memory improved after both diets, which the authors said may reflect practice on the tests.
• Alzheimer's disease: Phillips and colleagues randomized 26 people with Alzheimer's disease to 12 weeks of a modified ketogenic diet and 12 weeks of their usual diet with low-fat guidance. On keto, scores for daily function and quality of life improved. The cognitive test (the Addenbrooke's Cognitive Examination) rose by about 2 points, which was not statistically significant.
Xi and colleagues pooled 12 randomized trials with 707 older adults with mild cognitive impairment or Alzheimer's disease, covering ketogenic diets and related ketogenic strategies. Ketogenic strategies improved overall cognition (SMD = 0.34), memory (0.53) and language (0.43), with no significant effect on attention or executive function. They also raised total and LDL cholesterol.
An SMD (standardized mean difference) is a gap between groups in standard deviation units. Multiplying by 15 puts it on the familiar IQ-point scale, so 0.34 is about 5 points. That describes scores on cognitive screening tests in people with memory loss. It is not an IQ gain, and it comes from small trials of varied design.
Ketone drinks, MCT oil and epilepsy
Some products try to deliver ketones without the diet, through medium-chain triglyceride (MCT) oil or ketone esters.
• An MCT drink in mild cognitive impairment: Fortier and colleagues assessed 83 adults with mild cognitive impairment after six months on a ketogenic MCT drink or a placebo. The MCT group did better on four tests, including word recall, verbal fluency and naming. Nestlé Health Sciences funded part of the trial, and one author was a Nestlé employee.
• Exogenous ketones across studies: Bonnechère and colleagues pooled 29 study protocols with 1,117 participants and found a modest gain on cognitive tests with ketone supplements (SMD = 0.29), somewhat larger in healthy people (0.36) than in Alzheimer's disease (0.15). The results varied a great deal between studies, and two authors had worked for a company that sells a ketone ester while another held equity in ketone companies.
• Children with epilepsy: IJff and colleagues randomized 50 children and adolescents with drug-resistant epilepsy to the ketogenic diet or usual care. After about four months the keto group was rated less anxious and more productive, and showed better "activation" on cognitive tests. A review by van Berkel and colleagues found that objective tests confirm better alertness on the diet, but no improvement in global cognition. Fewer seizures probably explain part of the gain.
What about keto brain fog?
Many people report the opposite of sharper thinking in their first weeks of keto. Bostock and colleagues analysed 448 posts on online forums about "keto flu". The most common complaints were flu-like feelings, headache, fatigue, nausea, dizziness and "brain fog", peaking in the first week and fading after about four weeks. Forum posts are self-reports from a self-selected group, so they show what people experience, not how often it happens.
Anyone considering a ketogenic diet, especially people who take medicine for diabetes or blood pressure, who are pregnant, or who have kidney, liver or heart conditions, should talk to a doctor first. The medical ketogenic diet for epilepsy is run by specialist teams for a reason.
Frequently asked questions
Does keto make you smarter?
There is no evidence that it raises IQ in healthy people. Controlled trials in healthy adults found no difference in cognitive test scores between keto and higher-carbohydrate diets.
Can keto help memory in older adults?
Small trials in mild cognitive impairment and Alzheimer's disease report modest gains on memory and screening tests, and a 2026 meta-analysis found a pooled improvement (SMD = 0.34). Larger and longer trials are needed.
Do ketone drinks or MCT oil improve focus?
A 2026 meta-analysis found a small average improvement on cognitive tests with ketone supplements, but results varied widely and some authors had commercial ties to ketone products.
Why do I feel foggy when starting keto?
Brain fog, headache and fatigue are common complaints in the first weeks, often called "keto flu". Forum reports suggest they usually fade within about a month.
Does keto improve thinking in epilepsy?
Children on the diet were rated more alert and active in one randomized trial, but reviews found no improvement in global cognition. Reduced seizures likely explain part of the benefit.
The takeaway
Keto has not been shown to make healthy people smarter. Trials in healthy adults found no cognitive benefit, and none measured IQ. Modest gains appear in older adults with memory loss, and the diet's original role in treating epilepsy remains its best-supported use. If you want an accurate picture of your reasoning ability, take the RIOT IQ test.
References
1. Xi, L., Wan, J., Hua, Y., Guo, M., Du, J., Luo, X., & Yu, H. (2026). Effects of ketogenic diet on cognitive impairment in older adults: A systematic review and meta-analysis. Archives of Gerontology and Geriatrics, 151, 106409. [doi.org/10.1016/j.archger.2026.106409](. doi.org
2. Neal, E. G., Chaffe, H., Schwartz, R. H., Lawson, M. S., Edwards, N., Fitzsimmons, G., Whitney, A., & Cross, J. H. (2008). The ketogenic diet for the treatment of childhood epilepsy: A randomised controlled trial. The Lancet Neurology, 7(6), 500-506. [doi.org/10.1016/s1474-4422(08)70092-9](. doi.org
3. Castellano, C. A., Nugent, S., Paquet, N., Tremblay, S., Bocti, C., Lacombe, G., Imbeault, H., Turcotte, É., Fulop, T., & Cunnane, S. C. (2015). Lower brain 18F-fluorodeoxyglucose uptake but normal 11C-acetoacetate metabolism in mild Alzheimer's disease dementia. Journal of Alzheimer's Disease, 43(4), 1343-1353. [doi.org/10.3233/JAD-141074](. doi.org
4. Iacovides, S., Goble, D., Paterson, B., & Meiring, R. M. (2019). Three consecutive weeks of nutritional ketosis has no effect on cognitive function, sleep, and mood compared with a high-carbohydrate, low-fat diet in healthy individuals: A randomized, crossover, controlled trial. The American Journal of Clinical Nutrition, 110(2), 349-357. [doi.org/10.1093/ajcn/nqz073](. doi.org
5. Brinkworth, G. D., Buckley, J. D., Noakes, M., Clifton, P. M., & Wilson, C. J. (2009). Long-term effects of a very low-carbohydrate diet and a low-fat diet on mood and cognitive function. Archives of Internal Medicine, 169(20), 1873-1880. [doi.org/10.1001/archinternmed.2009.329](. doi.org
6. Tay, J., Zajac, I. T., Thompson, C. H., Luscombe-Marsh, N. D., Danthiir, V., Noakes, M., Buckley, J. D., Wittert, G. A., & Brinkworth, G. D. (2016). A randomised-controlled trial of the effects of very low-carbohydrate and high-carbohydrate diets on cognitive performance in patients with type 2 diabetes. British Journal of Nutrition, 116(10), 1745-1753. [doi.org/10.1017/s0007114516004001](. doi.org
7. Krikorian, R., Shidler, M. D., Dangelo, K., Couch, S. C., Benoit, S. C., & Clegg, D. J. (2012). Dietary ketosis enhances memory in mild cognitive impairment. Neurobiology of Aging, 33(2), 425.e19-425.e27. [doi.org/10.1016/j.neurobiolaging.2010.10.006](. doi.org
8. Neth, B. J., Mintz, A., Whitlow, C., Jung, Y., Solingapuram Sai, K., Register, T. C., Kellar, D., Lockhart, S. N., Hoscheidt, S., Maldjian, J., Heslegrave, A. J., Blennow, K., Cunnane, S. C., Castellano, C. A., Zetterberg, H., & Craft, S. (2020). Modified ketogenic diet is associated with improved cerebrospinal fluid biomarker profile, cerebral perfusion, and cerebral ketone body uptake in older adults at risk for Alzheimer's disease: A pilot study. Neurobiology of Aging, 86, 54-63. [doi.org/10.1016/j.neurobiolaging.2019.09.015](. doi.org
9. Phillips, M. C. L., Deprez, L. M., Mortimer, G. M. N., Murtagh, D. K. J., McCoy, S., Mylchreest, R., Gilbertson, L. J., Clark, K. M., Simpson, P. V., McManus, E. J., Oh, J. E., Yadavaraj, S., King, V. M., Pillai, A., Romero-Ferrando, B., Brinkhuis, M., Copeland, B. M., Samad, S., Liao, S., & Schepel, J. A. C. (2021). Randomized crossover trial of a modified ketogenic diet in Alzheimer's disease. Alzheimer's Research & Therapy, 13(1), 51. [doi.org/10.1186/s13195-021-00783-x](. doi.org
10. Fortier, M., Castellano, C. A., St-Pierre, V., Myette-Côté, É., Langlois, F., Roy, M., Morin, M. C., Bocti, C., Fulop, T., Godin, J. P., Delannoy, C., Cuenoud, B., & Cunnane, S. C. (2021). A ketogenic drink improves cognition in mild cognitive impairment: Results of a 6-month RCT. Alzheimer's & Dementia, 17(3), 543-552. [doi.org/10.1002/alz.12206](. doi.org
11. Bonnechère, B., Stephens, E. B., Boileau, A. C., Ducker, M., & Stubbs, B. J. (2026). The effect of exogenous ketone bodies on cognition across health and disease: A systematic review and meta-analysis. Frontiers in Nutrition, 13, 1802531. [doi.org/10.3389/fnut.2026.1802531](. doi.org
12. IJff, D. M., Postulart, D., Lambrechts, D. A. J. E., Majoie, M. H. J. M., de Kinderen, R. J. A., Hendriksen, J. G. M., Evers, S. M. A. A., & Aldenkamp, A. P. (2016). Cognitive and behavioral impact of the ketogenic diet in children and adolescents with refractory epilepsy: A randomized controlled trial. Epilepsy & Behavior, 60, 153-157. [doi.org/10.1016/j.yebeh.2016.04.033](. doi.org
13. van Berkel, A. A., IJff, D. M., & Verkuyl, J. M. (2018). Cognitive benefits of the ketogenic diet in patients with epilepsy: A systematic overview. Epilepsy & Behavior, 87, 69-77. [doi.org/10.1016/j.yebeh.2018.06.004](. doi.org
14. Bostock, E. C. S., Kirkby, K. C., Taylor, B. V., & Hawrelak, J. A. (2020). Consumer reports of "keto flu" associated with the ketogenic diet. Frontiers in Nutrition, 7, 20. [doi.org/10.3389/fnut.2020.00020](. doi.org
Hero image: A half cut avocado, by Billjones94, CC0. Via Wikimedia Commons.
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