Dementia and dietary sugars

This content is authored by Registered Dietitian, Juliette Kellow.

Dementia

Dementia is the name used to describe a group of symptoms linked to an ongoing decline in brain function resulting from damage to brain cells.

According to the World Health Organization, an estimated 57 million people were living with dementia worldwide in 2021 (1). By 2050, this figure is expected to rise to 153 million (2), with current estimates indicating there is one new case of dementia in the world every three seconds (3). Dementia is the seventh leading cause of death globally and affects more women than men, both in terms of living with symptoms and caring for others with them (1).

Although dementia is not a disease itself, it often stems from underlying diseases that damage brain cells and impair brain function. While dementia is more common in older people, it is not a natural part of ageing, as symptoms can occur at any age (4). Symptoms can vary depending on the cause and the part of the brain affected. Common symptoms include memory loss, difficulties with communication, confusion, changes in behaviour and personality, and problems with everyday mental tasks. Symptoms cannot be reversed, generally worsen over time, and can dramatically affect daily living.

The two most common causes of dementia are Alzheimer’s disease and vascular dementia

Alzheimer’s disease contributes to around 60-70% of dementia cases globally (1) and occurs when two substances, amyloid and tau, build up in the brain, forming structures called ‘plaques’ and ‘tangles’ that damage the brain cells. There is also a drop in chemical messengers (neurotransmitters) in the brain, which hinders the communication and signalling between brain cells (5).

Vascular dementia occurs when blood supply to the brain is reduced, depriving brain cells of oxygen and nutrients, causing them to stop working properly or die. This happens when blood vessels in the brain are damaged or blocked, often as a result of a stroke, high cholesterol, diabetes, or heart disease (6).

Risk factors for dementia

Research from the Lancet Commission on Dementia (experts assembled by The Lancet) suggests that almost half – 45% – of all global cases of dementia could be prevented or delayed by tackling and eliminating 14 risk factors (7). These include:

In early-life

Less education

In mid-life

Hearing loss
High levels of LDL or ‘bad’ cholesterol
Depression
Traumatic brain injury
Physical inactivity
Diabetes
Smoking
High blood pressure
Obesity
Excessive alcohol consumption

In later-life

Social isolation
Air pollution
Visual loss

The Lancet Commission on Dementia reviewed research on diet and dementia but concluded that there was insufficient evidence to identify any specific foods, nutrients or dietary patterns that increase dementia risk.

However, diet can play a part in protecting against, or increasing, the chances of developing four of the risk factors: raised LDL cholesterol, type 2 diabetes, high blood pressure, and obesity. These account for around 12% of all cases of dementia (7). This suggests that diet may indirectly affect dementia risk through its impact on other health conditions. For more information on these health conditions and dietary sugars, see the links below.

Heart disease and dietary sugars

Diabetes and dietary sugars

Obesity and dietary sugars

Dietary sugars and the risk of dementia

Despite the Lancet Commission on Dementia finding no evidence that specific nutrients, foods, or dietary patterns contribute to dementia risk, several recent large-scale studies have reported a link between dementia risk and higher intakes of sugars (8, 9, 10, 11). However, these are all prospective cohort studies (a form of observational research), so although they show an association, the findings do not prove that higher intakes of sugars cause dementia. Furthermore, these studies used participants from the same source – the UK Biobank – so rather than showing four independent pieces of evidence linking high sugar intakes to increased dementia risk, they instead show consistent analyses of the same data.

Beyond the Lancet Commission, the World Health Organization (WHO) provides guidelines to reduce the risk of cognitive decline and dementia (12). These include nutrition-related recommendations, though none specifically mention sugars. The guidelines:

• Recommend a healthy, balanced diet based on the WHO healthy diet advice.

• Recommend a Mediterranean-style diet for adults with normal cognition and mild cognitive impairment.

• Do not recommend taking supplements of B vitamins, vitamin E and polyunsaturated fatty acids or multi-complex supplements to specifically reduce the risk of cognitive decline and/or dementia, as there is insufficient evidence to support their use.

The role of dietary sugars in people living with dementia

Carbohydrates are an important source of energy for the body, and the brain depends on glucose as its main energy source. A continuous supply of glucose from the bloodstream is needed to support normal brain function (13). Glucose is produced from the breakdown of carbohydrates during digestion. It is then absorbed into the bloodstream and transported to cells throughout the body, including brain cells, where it is used for energy or is stored for later use. This makes the carbohydrates food group an important part of a healthy diet to support normal brain function (14). In people living with dementia, the brain may use energy less efficiently (15), making it especially important to maintain an adequate glucose supply to help reduce further decline in cognitive function.

Symptoms of dementia can affect eating and drinking habits, making it harder for people living with dementia to meet energy needs and stay nourished and hydrated. This can worsen overall health, reduce quality of life, and further impair cognitive function, compounding dementia symptoms (16). Weight loss is common in dementia (16), and research shows that amongst people living with dementia in long-term care, 27% are malnourished and a further 57% are at risk of malnutrition (17). Dehydration is also common and can cause confusion, impair memory, and reduce concentration, potentially worsening dementia symptoms (18). For these reasons, an energy-sufficient and nutrient-rich diet, together with adequate hydration and good dental hygiene practices, is a priority for those living with dementia.

The role of dietary sugars in dementia

Sugars from all dietary sources can play a useful role by contributing energy to the diet, particularly when included in nutrient-rich foods and drinks as part of a healthy, balanced diet. Sweetness can also improve the appeal and palatability of foods and drinks, particularly where there is a loss of smell, taste, or appetite – all of which are common in dementia.

Sweet foods may also carry nostalgic associations and evoke positive memories. Evidence suggests that many people living with dementia develop a preference for sweet foods. For example, studies of Alzheimer’s disease have found a preference for sweet foods in between 5% to 39% of people (19). While the reasons for this are not fully understood, changes in taste perception may play a role. Small studies suggest sweetness may be one of the last taste sensations to decline (20), making sweeter flavours easier to detect and more enjoyable.

Other theories suggest changes in the brain’s reward system may increase preference for sweeter foods (21). It has also been suggested that a preference for sweetness could be a compensatory response to deliver more glucose to the brain, although there is little evidence to support this explanation.

Providing foods and drinks that people enjoy and prefer is an important part of dementia care. In its Guideline on Nutrition and Hydration in Dementia, the European Society for Clinical Nutrition and Metabolism (ESPEN) recommends that individual habits, preferences, abilities, and behaviours around eating and drinking should be assessed and considered wherever possible (16).

There is no evidence that removing sweet foods and drinks slows the progression of dementia. ESPEN’s Guideline on Clinical Nutrition and Hydration in Geriatrics states that dietary restrictions that limit intake may be harmful and should be avoided (22). The guideline also recommends offering a variety of drinks based on individual preferences to support hydration and enjoyment, including tea, coffee, and sweet beverages such as flavoured water, soft or sports drinks, fruit juices, and smoothies.

Good oral hygiene for all persons with dementia, and individualised advice should be provided for those who are also living with diabetes. However, there are instances where nutrient-rich foods and drinks that are sweetened with sugars may help promote eating and drinking among people living with dementia.

Is a ‘keto diet’ beneficial for dementia?

Ketogenic or ‘keto diets’ are characterised by very low carbohydrate intake – typically 20-50g a day (23) – alongside higher fat intakes. These diets aim to switch the body's metabolism from using glucose as its primary energy source to using fat, producing ketones that can be used by the brain for energy. Impaired glucose metabolism in the brain has been observed in the early stages of dementia (15), leading to interest in ketogenic diets and other ketogenic interventions as a potential way to provide an alternative fuel source for brain cells.

Several small trials and systematic reviews have looked at the impact of ketogenic interventions in people with mild cognitive impairment or Alzheimer’s disease. However, the evidence is limited, and findings have been inconsistent. As a result, ESPEN’s Guideline on Nutrition and Hydration in Dementia concludes that there is currently no convincing evidence to recommend ketogenic interventions to improve cognitive function or prevent further cognitive decline. The guideline also highlights that keto diets can limit food choices and may increase the risk of malnutrition in people living with dementia (16).

Summary

Current scientific evidence does not show that eating sugars causes dementia. At present, the strongest evidence for dementia risk factors comes from the Lancet Commission on Dementia. Further research in diverse populations is needed.

Last reviewed March 2026. Next review due March 2029.