Sci&Tech Writer Madison Harding-White investigates recent research linking Alzheimer’s disease and diet

A Neuroscience graduate interested psychology, debate and sustainable lifestyles.
Images by porssella

Responsible for 60-80% of the 50 million cases of dementia worldwide, Alzheimer’s Disease can be extremely difficult to manage – with patients often becoming confused, amnesiac and even psychotic. It is thought that Alzheimer’s Disease develops due to abnormal deposition of amyloid beta proteins in the brain, which form extracellular plaques. These plaques are then thought to promote the formation of insoluble, twisted fibres (neurofibrillary tangles) inside brain neurones, together resulting in cell dysfunction and cell death.

Slowing the deposition of these plaques may therefore hold the key to slowing the onset of the disease, preserving patient quality of life for longer and reducing the burden of care. In promising recent research, diet has been suggested as a potentially adaptive means to do this.

In a longitudinal study from Valentina Berti and colleagues, 70 cognitively normal participants aged 30-60 years were measured for their adherence to a Mediterranean diet- one containing high levels of fruit, vegetables and cereals with limited animal products. When comparing 2 PET scans of participant brains taken at least 2 years apart, participants with a higher adherence to a Mediterranean diet had lower progress rates of amyloid beta deposition – indicating they would have a slowed progression of the disease.

70 cognitively normal participants aged 30-60 years were measured for their adherence to a Mediterranean diet

These results have been further supported by research in animal subjects, where adherence to a diet high in meat and dairy products was shown to promote cerebral oxidative stress in amyloid beta precursor proteins, a major risk factor for amyloid beta protein deposition.  These results suggest diets high in fruit, vegetables and cereals could have the potential to slow down this plaque deposition. 

This could be due to the higher consumption of vitamins C, A and E in plant rich diets, as these have been reported as potentially neuroprotective – preventing the formation of amyloid beta fibrils. Furthermore, high levels of saturated fat and cholesterol, commonly found in meat and dairy products, have also been negatively implicated in Alzheimer’s disease – with rodent subjects showing impaired memory and learning after consuming such a diet.

debate still remains regarding the inclusion of meat and fish within the diet

However, debate still remains regarding the inclusion of meat and fish within the diet. This is of particular prominence as adherence to veganism (a diet void of any animal products) has greatly increased in the UK. Whilst the vegan diet frequently champions a high fruit and vegetable consumption alongside a low intake of saturated fats, further nutrient intake issues relevant to Alzheimer’s disease can be produced. The polyunsaturated omega-3 docosahexaenoic acid (DHA) has been widely implied to reduce the risk of Alzheimer’s, with lower levels being found in the brain of those with the disease.

Concerningly for vegans, DHA is predominantly found in fish and eggs, with the only vegan option the relatively inaccessible algae. Whilst flaxseeds and other plant sources can be rich in omega 3, this takes the form of alpha-linolenic acid (ALA), of which only 0-4% is reportedly converted to DHA in the body. This could lead to deficiency issues, potentially influencing the speed of Alzheimer’s progression in such individuals. Additionally, further research has linked high soya intake, a common ingredient in vegan faux-meats and milks, to Alzheimer’s disease. Previous studies also demonstrated cerebral degeneration and shrinkage in relation to intake of tofu. This suggests that further research is required to clarify the impact of a vegan diet on later Alzheimer’s acquisition to ensure consumers can make informed choices about their diet.