The Effects of Diet on Alzheimer's Disease

The food we consume not only gives us energy to keep going, but it can also have an impact on our brain health. The nutritional contents of our diet will affect our physiology (how our body works) and could influence risk factors for developing Alzheimer’s disease (AD).¹

Alzheimer’s disease is a neurodegenerative disease that impairs memory and other cognitive functions. Whilst our diet does not directly cause AD, it can be a potential risk factor. Food sources that contain refined carbohydrates are high in saturated fat, have increased sugar content, excessive cholesterol, and processed animal products can raise the chances of developing Alzheimer’s disease.^1,2

This article will explore the effects of different diets on Alzheimer’s disease, so if you want to learn about the foods that might be the most beneficial for reducing the risk of cognitive impairment, scroll on.

Understanding alzheimer's disease

Alzheimer’s disease is the most common type of dementia, which causes memory loss and affects cognitive skills and behaviour. It is caused by an abnormal accumulation of certain proteins in the brain, which leads to neuronal ( nerve cell) damage and cell death.³

Even though it is not quite clear what sets off this neurocognitive disorder, there are many risk factors which contribute to developing AD, including:

• Age
• Genetics
• Family history
• Exposure to certain metals (like aluminium), physiological metal imbalance, and metal interactions with certain genes
• Traumatic brain injury
• Diet
• Obesity
• Diabetes
• (Cardio)vascular disease
• Immune system dysfunction
• Psychiatric factors (like depression or stress)⁴

The relationship between diet and alzheimer's disease

Nutritional factors and cognitive health

The brain's nutritional requirements

For the brain to develop correctly and perform all its mechanisms efficiently, it needs the following nutritional components at the correct levels:

• Glucose⁵
• Lipids
• Iron
• Zinc
• Iodine
• Copper
• Selenium
• Choline
• Vitamin A
• B vitamins
• Vitamin D
• Omega-3
• Omega-6
• Amino acids ¹

The concept of neuroprotective foods

There is this notion that foods not only have nutritional and energetical values but also have health benefits due to the bioactive elements they contain, such as vitamins, minerals, and antioxidants. Some of these components contribute to the brain being healthy, boosting memory, and potentiating its optimal cognitive functioning, hence foods containing them are known as neuroprotective foods.⁶

While a neuroprotective diet might not prevent or be the cure for a neurological disorder, it may reduce the risk of experiencing it. That is why it is important to try to keep a balanced diet. 

Types of diets and their impact

Several types of diets have been investigated due to their potential benefit in helping prevent the development of  AD. They will be reviewed below in relation to this.

The mediterranean diet

The Mediterranean diet (MD) is rich in fruit, vegetables, whole grains, plant proteins – e.g. legumes, seeds and nuts – healthy fats such as olive oil, omega-3 rich foods and fibre, with a moderate intake of fish, poultry and dairy, and is low in red meat, refined grains, refined sugar, and processed foods. 

It has been linked to a reduced risk for AD, and its neuroprotective effects have been attributed to the bioactive phytochemicals present in vegetables, fruits, and olive oil, which feature heavily in the diet (as mentioned above). This is because they contribute to lowering neuroinflammation, reducing oxidative stress, decreasing the accumulation of the proteins responsible for AD, and maintaining optimal cerebrovascular function (blood flow in the brain).^{7, 8} 

A study following healthy middle-aged participants’ adherence to this diet indicated that those who adhered to it more fully showed lower beta-amyloid plaque deposition, normal brain glucose consumption, and reduced AD biomarkers compared to those who had low adherence to the Mediterranean diet.⁹

Another study that looked at healthy and high-risk older individuals confirmed that those with greater adherence to the Mediterranean diet had healthier brain tissue, better memory, and less abnormal protein accumulation.¹⁰ However, it noted the necessity for more longer-term and interventionist studies.

Therefore, there is evidence that suggests that sticking to the Mediterranean diet could have positive effects on the brain’s health.

The DASH (dietary approaches to stop hypertension) diet 

The DASH diet is a dietary approach that focuses on lowering blood pressure. This diet is, likewise, rich in fruits, vegetables, nuts, polyunsaturated healthy fats, whole grains, legumes and fibre, with foods providing high intake levels of magnesium, calcium, and potassium. It is a low-sodium diet, as salt is restricted, and there is no consumption of red meat or refined sugars and a very much reduced intake of saturated fatty acids and cholesterol.¹¹

There is an established causal relationship between blood pressure and the appropriate functioning of the brain. Hypertension can be a risk factor in developing Alzheimer’s disease.¹² Therefore, a diet that also lowers blood pressure might be a good protective measure against AD.

There is research that suggests that the DASH diet has a positive impact on cognition and can lower the risk of AD.¹¹ However, studies usually investigated individuals who had food intake from both the DASH and Mediterranean diet. Therefore, it would be useful to conduct research focussed on the effects on AD of solely the DASH dietary approach. 

The MIND diet (mediterranean-DASH diet intervention for neurodegenerative delay)

The MIND diet is a mix of the two diets discussed above, and its main food groups include green leafy vegetables, berries, legumes, nuts, whole grains, poultry, fish, olive oil, and red wine. However, contrary to the Mediterranean and DASH diets, this one also includes a balanced consumption with a moderate intake of saturated fats, red meat, sugar, butter, and cheese.¹¹

Research has indicated that adherence to the MIND dietary pattern (with both high and moderate compliance with the diet) might contribute to decreasing the risk of developing AD.¹³ Additionally, another study has shown a substantially slower decline in memory and perception with age in individuals who followed a MIND diet.¹⁴

Ketogenic diet

Recently, there has been increased media and public focus on the Ketogenic diet, which involves reducing carbohydrate intake and increasing fat ingestion for weight loss. There has also been some research investigating whether the ketone bodies produced during adherence to the ketogenic diet are neuroprotective against AD. 

While it appears that this way of eating might have some positive effects on cognition (which might be linked to the regulation of glucose in the brain and providing the brain with alternate ‘fuel’), research is still limited, so more studies are warranted to confirm or deny this.⁷

The western diet

The Western diet (WD) is considered a high-risk factor for Alzheimer’s disease. It is the modern pattern of eating characterised by ultra-processed foods, high levels of sugars, saturated fatty acids, and cholesterol. 

Scientists have found that ingesting this diet may lead to:

• Poor memory
• Reduced synaptic plasticity
• Higher accumulation of the abnormal proteins responsible for AD
• Blood-brain barrier damage
• Neuroinflammation and neurodegeneration
• Elevated cholesterol levels
• Obesity¹⁵

Therefore, if you are concerned about your chances of suffering from dementia, you could try to avoid pre-packaged meals, fast food, sweet confectionery, and sugary drinks.

Caloric intake and alzheimer's disease

It is important that individuals suffering from AD have a carer or someone who monitors their caloric intake because, due to their condition, they might forget what and how often they have eaten, which could result in binge eating or not eating sufficiently. Consequently, this could cause further damage as well as other types of problems. Moreover, calorie restriction can have a positive impact on the brain and, in one study, resulted in improved ‘recognition memory’.¹ 

However, please consult an appropriate health professional if you are considering this approach. 

The role of gut health and the microbiome

Before the brain gets its necessary nutritional components, the body needs to digest them, and the gut microbiome participates in this process. In addition, these microorganism elements of the digestive system help the gut and brain to communicate via the brain-gut axis. The gut and brain are in constant communication through nervous signalling and chemical messengers in the bloodstream. The helpful gut microbiota produces neurotransmitters involved in the signalling and also releases the chemical messengers into the bloodstream. The gut microbiota is influenced by what you eat. For example, dietary fibre (largely obtained from plants) positively influences the digestive system and feeds the helpful gut microbiota.  Some studies have found a correlation between dietary fibre intake and good cognition and brain health. On the other hand, foods belonging to the Western dietary pattern might have harmful effects impairing brain health and performance.¹ Hence, a healthy diet is also important to ensure efficient, positive brain-gut axis communication. 

Diet as a preventive measure

Having a well-balanced diet like the ones mentioned above, full of vegetables, fruits, healthy oils, omega-3, and proteins, can help you reduce the risk of suffering from Alzheimer’s disease. 

However, for this to have the desired effect, you should also consider adopting the following lifestyle factors:

• Exercising
• Maintaining proper hydration
• Being socially active
• Taking care of your mental health
• Keeping your mind active
• Treating any health issues like cardiovascular problems, high cholesterol, diabetes, and obesity 
• Controlling and limiting your alcohol intake

Please be aware that these are preventive measures that might decrease your chances of experiencing this type of dementia. However, they are not a method of treatment, as, unfortunately, there is currently no cure for this cognitive decline. Moreover, doing all the activities above is not a 100% guarantee of never experiencing Alzheimer’s, especially considering there are other factors that can play a role in its development.^{1, 8, 11,15}

Diet as a management tool

Unfortunately, if you or someone close to you has been diagnosed with Alzheimer’s disease, there is no medication yet to make it go away completely. Nonetheless, that does not mean there aren’t things you can do to boost health. 

Ensuring AD patients maintain good nutrition is important, as they might not be able to do so for themselves anymore or could even forget about eating. A balanced diet, as described above, may slow down cognitive decline. 

Here are some tips that could help people with Alzheimer’s when eating:

• Integrate a diet rich in fruits, vegetables, whole grains, and healthy oils and low in refined sugars, unhealthy fats, and salt. But ensure the diet is adapted to the person’s needs.
• Ensure adequate hydration by adding small cups of water with each meal, as well as having other fluids such as tea or fruit smoothies.
• Limit potential distractions while eating (like TV, phones, patterned plates, unnecessary cutlery, etc.) so that patients can focus on their food.
• Make sure the food is distinguishable from other surrounding objects, helping individuals to recognise it. Making it finger food helps individuals feed themselves, and food served in smaller portions is easier to manage.
• Allow the person with AD to be as independent as possible and only intervene when needed, for example, if they cannot get the food onto their cutlery or are choking.

You might also encounter some challenges in maintaining a proper diet for AD patients due to decreased appetite that arises from a variety of factors, including:

• They do not recognise the food
• Medications might have a negative impact on appetite 
• They cannot taste the food anymore, or their taste is altered – because their sensory impairment affects their taste buds and the sensory processing of taste.
• Lack of exercise – so physical activity is no longer stimulating appetite 
• Foods might be too difficult to chew and swallow, and the sensing of texture is altered

In this case, you should consult a physician and talk to sources of support to find some resources that could help. 

Summary

A well-balanced dietary pattern, such as the Mediterranean diet, rich in fruits, vegetables, legumes, whole grains, healthy oils, and fish, could decrease the risk factors for Alzheimer’s disease. This is because the nutritional components of these foods, such as antioxidants, minerals, or vitamins, might play a role in enhancing cognition and delaying cognitive decline. On the other hand, a diet full of sugars, saturated fats, and ultra-processed foods is high in risk factors for developing dementia.

It is important to combine a healthy diet with exercise alongside other lifestyle factors, for improved health. Furthermore, more research is necessary regarding the effects of diet on AD because some mechanisms of action are still unclear, and dietary approaches might be a fruitful target for integration into the management of the condition with the aim of slowing its progression.