The GL of Your Diet Determines Your Future Dementia Risk
by Patrick Holford
Why Blood Sugar Exposure Matters More Than Sugar Itself
Your brain uses more glucose for energy than any other organ in the body.
From that simple fact comes a widespread assumption: that sugar fuels the brain and therefore more sugar must mean more mental energy.
In reality, the relationship between blood sugar and brain health is more complex.
A large UK Biobank study, published in the International Journal of Epidemiology, investigated the relationship between dietary glycaemic index (GI), glycaemic load (GL) and future dementia risk in more than 200,000 participants (1).
So what did the researchers actually find?
What did the study find about glycaemic load and dementia?
A 2025 study published in the International Journal of Epidemiology investigated the relationship between dietary glycaemic index (GI), glycaemic load (GL) and future dementia risk in 202,302 dementia-free participants from the UK Biobank.
Researchers estimated participants’ dietary GI and GL using 24-hour dietary questionnaires and examined their subsequent risk of all-cause dementia, Alzheimer’s disease and vascular dementia.
The relationship was not simply a case of “the lower, the better”. Instead, the researchers found a J-shaped relationship between glycaemic load and dementia risk.
Above a dietary GL of approximately 111, increasing GL was associated with a higher risk of dementia. After adjusting for potential confounding factors, GL above this point was associated with a 14.5% higher relative risk of dementia. Similar patterns were observed for Alzheimer’s disease and vascular dementia.
Glycaemic index showed a different pattern. GI values below approximately 49 were associated with a lower risk of dementia, suggesting that both the quality and quantity of carbohydrate in the diet may be important.
These findings sit within a wider body of research investigating how diet relates to brain health. Food for the Brain research into diet and cognitive function has also examined self-reported dietary patterns alongside cognitive test results, including the relationship between sugar intake and cognitive performance.
What does this research tell us?
The findings strengthen the evidence linking carbohydrate quality, overall glycaemic load and metabolic health with future brain health. They also suggest that looking only at the GI of individual foods may miss part of the picture, because glycaemic load takes into account both the glycaemic index and the amount of carbohydrate consumed.
However, this was an observational study, not a clinical trial. It can show an association between dietary GI and GL and subsequent dementia risk, but it cannot prove that a high-GL diet causes dementia or that lowering GL will prevent it. Dietary intake was also estimated using self-reported dietary questionnaires.
For practical guidance on lowering the glycaemic load of your diet, including foods to choose, simple swaps and examples of low GL meals, see Domain 1: Eat a low Glycaemic Load (GL) diet.
How Much Sugar Your Body Really Needs
As petrol is for your car, glucose is the primary fuel for your body. Glucose is the main fuel used by all cells.
There is also another fuel, ketones, much like cars can also run on electricity. We too are metabolic hybrids.
Now here is an astonishing fact. Your body contains around 100,000 kilometres of blood vessels. Your brain alone has around 1,000 kilometres of them. These vessels supply energy to around 30 trillion cells, each containing roughly 1,000 mitochondria, the tiny energy factories that power life.
And yet, across this entire system, there only needs to be around 4 grams of glucose in your bloodstream at any one time. That is one teaspoonful. That is all that is required for every cell in your brain and body to have energy at that moment.²
Glycaemic load (GL) takes into account both the glycaemic index (GI) of a food and the amount of available carbohydrate in a serving, giving a more practical indication of its likely impact on blood glucose.
The glycaemic load of a food depends on two things:
• the quality of the carbohydrate
• the quantity eaten
Quality refers to how fast glucose is released, known as the glycaemic index (GI). Fibre and protein slow this release. This is why white rice has a higher GI than brown rice, which contains fibre. Eat rice with fish, beans or meat, and the protein slows the release further.
GL also depends on portion size. A small serving of brown rice with fish is low GL. A large serving of white rice, even with fish, is high GL.
How Excess Blood Glucose Can Affect the Brain
What happens if you consume far more glucose than the body needs?
A can of sugary fizzy drink contains around 35 grams of sugar. That is roughly nine times more glucose than the total amount normally circulating in your bloodstream.
This excess is toxic. It damages blood vessels and the tissues they supply. Diabetes is diagnosed precisely because excess sugar damages the kidneys, eyes and nerves. The brain is no exception.
“The brain needs more energy than any other organ, so it contains the most mitochondria. Sugar damages mitochondria,” says Professor Robert Lustig, Professor of Neuroendocrinology at the University of California, San Francisco. If you have read Upgrade Your Brain or Alzheimer’s: Prevention is the Cure, you will already know that high sugar intake, sugary drinks and ultra processed foods increase dementia risk, worsen memory even in young people, and are associated with measurable shrinkage of brain regions involved in memory in teenagers.
Are You Eating Too Much Hidden Sugar?
The simplest way to assess your long term blood sugar exposure is to measure HbA1c.
HbA1c measures the proportion of haemoglobin that has glucose attached to it (glycated haemoglobin), providing an indication of average blood glucose levels over the previous two to three months. An HbA1c of 6.5% (48 mmol/mol) or above is one of the thresholds used in the diagnosis of diabetes.
For optimal health you want to be below 5.4%, and ideally below 5%.
HbA1c is such a strong indicator of blood sugar resilience that it is included in Food for the Brain’s 5-in-1 DRIfT home blood test kit.
Whats Does It Mean For Your Diet?
The research does not show that there is one ideal glycaemic load for everyone, or that lowering GL will prevent dementia. However, it adds to evidence suggesting that the quality and quantity of carbohydrate we eat, and their effect on blood glucose, may be important for long-term brain health.
In practical terms, a lower GL way of eating means choosing fewer refined and rapidly digested carbohydrates, while favouring foods that have a gentler effect on blood glucose, such as beans and lentils, non-starchy vegetables, whole fruits, nuts and seeds.
For practical guidance, food swaps and examples of lower GL meals, see Domain 1: Eat a low Glycaemic Load (GL) diet.
The Proof Is in Your HbA1c
Red blood cells live for around three months. Follow a low GL diet for three months, then retest HbA1c.
This approach is detailed in The Low GL Diet Cookbook. Specific supplements can accelerate recovery, including fibre such as glucomannan, chromium and cinnamon compounds to improve insulin sensitivity, and HCA from tamarind to promote glucose burning rather than storage.
What to Do Next
If glycaemic load affects dementia risk, the next step is simple: measure, act, and check again.
Test your blood sugar resilience.
HbA1c shows how much sugar damage has occurred over the last three months. It is included in Food for the Brain’s DRIfT 5-in-1 home test, alongside other key brain health markers. If HbA1c is high, a low GL diet gives you a clear way to bring it down.
Check how your brain is functioning now.
The free Cognitive Function Test takes around 20 minutes and provides an objective snapshot of memory, attention and processing speed. Many people spot early changes years before any diagnosis.
Make changes, then retest.
Follow a low GL diet for three months, then re-test HbA1c and cognitive function to see whether the changes are working.
Prevention works best when it is measured.
References:
- Novau-Ferré N et al. Glycemic index, glycemic load, and risk of dementia: a prospective analysis within the UK Biobank cohort. Int J Epidemiol. 2025.
- Wasserman DH. Four grams of glucose. Am J Physiol