• Sat. Jun 22nd, 2024

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Low fat and high carb diets may be bad for your brain


By Patrick Holford, Founder of the Food for the Brain Foundation

A low-fat diet may help reduce your calorie intake, but it could be bad for your brain and increase your risk of dementia. New evidence shows that brain cells clog up if they are presented with too much energy from sugar (glucose or fructose) that is derived from carbs rather than from fats. Type 2 diabetes, a consequence of too much sugar, almost doubles the risk for dementia.[1]

However, very high fat ‘ketogenic’ diets, which are low in carbs and contain almost no sugar, substantially reduce that risk.

The brain can derive a lot of its energy needs from ketones which come from fats. The brain also depends on omega-3 fats for signalling systems which enable us to think. Increased intake of omega-3, either from diet or supplements, or having a higher omega-3 blood level, cuts the risk for dementia by a fifth (20%), according to a study of over 100,000 people just published in the American Journal of Clinical Nutrition.[2] This means eating oily fish such as salmon, mackerel, sardines, and kippers or supplementing with fish oils. A UK Biobank study shows those supplementing fish oils have 12% less dementia.[3]

The trouble with carbs

The trouble with low fat diets and low-fat foods in general is that they are inevitably higher in carbohydrates, especially sugar. Carbohydrates are rapidly digested down to glucose which is an important brain fuel in the right quantity. However, eating too much refined ‘white’ carbohydrate on a regular basis, from sugar to white bread, rice or pasta messes up the glucose supply to the brain by promoting insulin resistance.[4] Insulin is the hormone that helps carry glucose into the brain and, with too much sugar and carbs in the diet, insulin receptors shut down, effectively going ‘deaf’. This is called insulin resistance and leads to a paradoxical increase in blood glucose, but poor supply into the brain. In adolescents with insulin resistance, cognitive abilities decline, and the area associated with Alzheimer’s shrinks.[5] Even slightly raised blood glucose level within the ‘normal’ range, from age 35, predicts increased risk for dementia several decades later.[6]

What’s the alternative?

Brain cells, however, can run on an alternative fuel: ketones, which are made in the liver from fat. Brain cells prefer to run on ketones when they are available, as these give the brain an energy boost. A newborn baby’s brain grows rapidly as a consequence of running on ketones. By consuming a kind of fat called medium chain triglycerides (MCTs), found in fatty foods such as oily fish and coconut oil, the body can make ketones and memory can improve. The exact fat that the liver makes ketones from most readily is called C8. Seven per cent of coconut oil is C8. Pure C8 oil is available in health food stores.

In two studies, one in those with pre-dementia (mild cognitive impairment)[7], another in those with Alzheimer’s[8], participants were given two tablespoons of a C8 oil. In both studies brain energy derived from ketones doubled. In those with pre-dementia this corresponded with measurable memory and cognitive improvements, but not in those already with Alzheimer’s. This positive effect, both in increased brain energy and cognition, does NOT happen if a person is given a glucose supplement. In fact, increasing glucose or fructose is linked to decreasing cognitive function.

Real life evidence

Alan is a case in point. Diagnosed with Alzheimer’s and vascular dementia in December 2022, he completed—with the support of his wife—the on-line Cognitive Function Test and dementia risk questionnaire at foodforthebrain.org. This test shows you what diet and lifestyle factors are driving your risk for dementia.

Following this, Alan lowered his intake of sugar and carbohydrates, started taking C8 oil every day and went ‘ketogenic’ five days a month, avoiding all carbs and eating high fat. He also increased exercise, became more mentally and socially active and supplemented omega-3 fish oils alongside B vitamins.

By March 2023, three months later, he had made vast improvements. “I’ve got my husband back from dementia” reported his wife, Dot. “His brain is working again. We can have normal conversations.”

Alan has joined a Morris dancing group and is back in the garden. “I had completely forgotten how to garden,” says Alan. “I had allotments for over 35 years, so it was a shock. Since I’ve been following foodforthebrain.org’s COGNITION programme I’ve had the seeds out, got the pots ready for planting and planned when and where things should go.”

They both noticed clear improvements when he goes ketogenic, eating a high fat, low carb diet. “A couple of times we’ve been out to dinner with friends and inevitably eaten more carbs and sugar. The next day his memory and concentration is definitely worse.” says Dot.

By cutting out all carbs (bread, rice, pasta and anything with sugar in it) and having more high fat foods such as oily fish, fattier meats, avocadoes, taramasalata (fish roe), nuts, seeds, beans and lots of green vegetables and salads with olive oil and a few berries, the body switches to running on ketones. A simple breath test, called Ketoscan Lite, or a ketone urine stick confirm the ‘switch’ to going ketogenic has happened. This normally takes up to three days, so it is best to do this for at least five to seven days a month.


Professor Stephen Cunnane, who heads the Brain Research Team at Sherbrooke University in Quebec, Canada, is an expert in the new science of ‘ketotherapeutics’. His research is focused on how both ketogenic high fat diets, but also giving C8 oil or supplementing ketones themselves, can help prevent Alzheimer’s, slow down cognitive decline, improve mood and lessen anxiety.

Our research shows that the areas of the brain that have trouble using glucose for energy are able to use ketones perfectly well, even in moderately advanced dementia. This may explain why many people later in life who are given a supplement of C8 oil or MCT oil have improvements on a battery of cognitive tests. They often feel it brings their brain power back to life,” says Cunnane.

Many people also report feeling calmer, less anxious and less depressed on ketogenic diets. A keto diet also definitely helps neurological conditions such as drug-resistant epilepsy. It may also help in Parkinson’s. In fact, high fat keto diets have been used successfully for over a hundred years to help children with epilepsy.

We are assessing whether combining exercise and a ketogenic supplement will help people with either dementia or Parkinson’s,” says Professor Cunnane, offering hope to those suffering with the disease.

Professor Stephen Cunnane presented an online webinar on ‘Ketones – a key brain fuel during aging’ for the charity foodforthebrain.org on 6 June 2023. This webinar explained how the brain uses ketones for fuel, how to implement a keto diet and the state of the science for keto diets and supplements for reducing cognitive decline and their potential as a treatment option to help prevent or arrest dementia, as well as other neurological diseases such as Parkinson’s and epilepsy.

If you’d like to or watch a video recording, please join and register at: https://foodforthebrain.org/event/ketonebrain/


Patrick Holford is a Nutrition and Mental Health expert & Founder of the Institute for Optimum Nutrition, VitaminC4Covid, and the charitable Food for the Brain Foundation, where he directs their Alzheimer’s prevention project. Patrick reads hundreds of studies a year assimilating the latest health breakthroughs and turning them into practical advice to make it easy for everyone to live a healthy life. He is author of 46 health books translated into over 30 languages. www.patrickholford.com


The Food for the Brain Foundation (foodforthebrain.org) is an educational and research charity, focussing on dementia prevention. It’s free online validated Cognitive Function Test, followed by the Dementia Risk Index questionnaire assessing eight drivers of dementia, including ‘brain fats’ and ‘low carbs & GL’ thus identifying those eating too many carbs and not enough brain fats, then advising them what to do.

Watch this film to understand how your brain makes energy from ketones https://foodforthebrain.org/cog-nition/your-brain-on-ketones-is-c8-oil-your-brains-next-best-friend/


The references below are to studies referred to. Enter the ‘doi number’ into google to find the full paper.

[1] https://foodforthebrain.org/is-sugar-killing-your-brain/

[2] Wei BZ et al Am J Clin Nutr. 2023 doi: 10.1016/j.ajcnut.2023.04.001.

[3] Huang Y et al Front Neurosci. 2022 doi: 10.3389/fnins.2022.910977

[4] https://foodforthebrain.org/is-sugar-killing-your-brain/

[5] Yau PL et al Pediatrics. 2012 doi: 10.1542/peds.2012-0324.

[6] Zhang X et al Alzheimers Dement. doi: 10.1002/alz.12641.

[7] Fortier M et al Alzheimers Dement. 2021 doi: 10.1002/alz.12206.

[8] Croteau E et al J Alzheimers Dis. 2018doi: 10.3233/JAD-180202

By mac