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New Evidence Shows Low Fat and High Carb Diets May Increase Your Dementia Risk

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New evidence shows that brain cells clog up if presented with too much energy from sugar (glucose or fructose) derived from carbs rather than fats. Type 2 diabetes, a consequence of too much sugar, almost doubles the risk for dementia.

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

The brain can derive much of its energy needs from ketones and fats. The brain also depends on omega-3 fats for signalling systems, enabling 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.

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.

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, an important brain fuel in the right quantity.

However, eating too much refined ‘white’ carbohydrate regularly, from sugar to white bread, rice or pasta, messes up the glucose supply to the brain by promoting insulin resistance. 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 to the brain.

In adolescents with insulin resistance, cognitive abilities decline, and the area associated with Alzheimer’s shrinks. Even slightly raised blood glucose level within the “normal” range from age 35 predicts increased risk for dementia several decades later.

What’s the alternative?

However, brain cells can run on an alternative fuel: ketones, made in the liver from fat. Brain cells prefer to run on ketones when available, giving the brain an energy boost. A newborn baby’s brain grows rapidly due to running on ketones.

The body can make ketones and improve memory by consuming medium-chain triglycerides (MCTs) in fatty foods such as oily fish and coconut oil. The fat the liver makes ketones from most readily is C8. 7% 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), and another in those with Alzheimer’s, 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.

In increased brain energy and cognition, this positive effect does not happen if a person is given a glucose supplement. 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 online Cognitive Function Test and dementia risk questionnaire at foodforthebrain.org. This test shows what diet and lifestyle factors drive 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, which was a shock.

Since following “foodforthebrain 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. “We’ve been to dinner with friends several times and inevitably eaten more carbs and sugar. The next day his memory and concentration are 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, confirms the “switch” to going ketogenic. This normally takes up to three days, so it is best to do this for at least five to seven days a month.

Ketotherapeutics

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 and giving C8 oil or supplementing ketones 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 can 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. 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 from the disease.

Professor Stephen Cunnane presented an online webinar on “Ketones – a key brain fuel during ageing” for the charity foodforthebrain on 6th 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 treatment options to help prevent or arrest dementia, as well as other neurological diseases such as Parkinson’s and epilepsy.


Patrick Holford is a nutrition and mental health expert and founder of the Institute for Optimum Nutrition, VitaminC4Covid, and the charitable Food for the Brain Foundation.

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