“For now, the food we eat is the most potent intervention available for disease prevention and treatment”
Valter Longo, PhD, Director of the Longevity Institute, University of Southern California.
When the British medical journal, The Lancet, published the 12 most common risk factors for Alzheimer’s disease and related dementias (ADRD) in 2019 they didn’t include diet as one. This was surprising considering the large volume of research linking unhealthy diets and particular foods such as sugar and saturated fat with ADRD. A spokesperson later explained that there were too many variables when it came to diet and that it is very difficult to link any particular food with ADRD in a conclusive way. But certain foods have since been proven to be associated with known risk factors, and in a simple process of eliminating these foods and eating foods known to promote better health we can substantially reduce the risk factors for developing cognitive decline, and, in the words of the World Health Organisation “until a cure is found reducing our risk is the best way to prevent ADRD.”
What are the risk factors associated with ADRD that certain dietary choices can mitigate against?
According to experts, there are three direct dietary-related risk factors:
Type 2 diabetes, obesity and consumption of ultra-processed foods.
Type 2 diabetes and Alzheimer’s disease are two of the fastest-growing health concerns worldwide. More and more, studies are showing that measures taken to prevent or treat diabetes will significantly slow the progression of symptoms of Alzheimer’s disease.
Scientific reviews have summarised that type 2 diabetes increases the likelihood of developing some form of ADRD by approximately 50%. It is associated with common features seen in ADRD including vascular damage, over-accumulation of amyloid-beta and tau (the damaged proteins seen as the most likely cause of Alzheimer’s disease), chronic inflammation, insulin resistance and blood-brain barrier damage. Science is now starting to refer to Alzheimer’s disease as type 3 diabetes. Because type 2 diabetes is such a risk factor for ADRD, diets that help reduce it confer neuroprotection.
Obesity, another diet-related disease, is also a major risk factor for ADRD. A new study published in the Lancet led by Imperial’s School of Public Health, London states that obesity is now a greater threat to global health than hunger. Calorie-dense meals, low in nutrition, cause weight gain which in turn can lead to chronic inflammation including brain inflammation. This is one of the main driving forces behind cognitive decline.
A recent article published in the Journal of Alzheimer's Disease stated that a typical Western diet, high in saturated fat causes an imbalance in our gut microbiome which interferes with our eating control mechanism, leading to obesity. This, in turn, promotes insulin resistance, chronic inflammation and cognitive decline. It also leads to disruption of our mitochondrial function (the part of our cells that make energy). When the mitochondria can’t produce enough energy, our brain cells, which require enormous amounts to maintain connections with other cells, begin to falter and connections between cells start to break up and memories are lost.
Consumption of ultra-processed foods (UPFs) has several negative effects on our brains due to their high content of added sugars, artificial ingredients, unhealthy fats, emulsifying agents, and general lack of essential nutrients.
Diets high in UPFs:
- can impair memory and learning because of their impact on areas of the brain such as the hippocampus, responsible for memory and learning.
- can disrupt blood sugar levels causing inflammation which is known to be associated with anxiety, and depression, a risk factor for ADRD
- can have addictive components including added fat, salt and artificial sweeteners which result in cravings and over-eating, exasperating obesity.
While an unhealthy diet leads to metabolic dysfunction, disease and cognitive decline, there is plenty of evidence that a healthy diet protects us against diseases that normally accompany ageing.
The APC Microbiome Institute at University College Cork has undertaken a great deal of research in this area and found in a recent study that eating a Mediterranean diet causes changes to the microbiome sufficient to improve cognitive function, memory, immunity and bone strength.
The Mediterranean diet is a mostly plant-based diet rich in nuts, seeds, fruits, vegetables, whole grains and legumes. The main fat is olive oil, usually extra virgin, and the diet also includes small amounts of fish, poultry, dairy, eggs and a little red wine. Red meat is rarely eaten and sweets and processed foods are generally avoided.
As our population ages the number of people suffering from chronic diseases such as Alzheimer’s disease and diabetes is increasing. Science now accepts that reactive oxygen species (ROS) and our natural ability to defend against them are involved in many ageing-related diseases. ROS are a natural biological byproduct that are necessary for cellular function but in excess become highly toxic and can cause harmful stress responses that lead to chronic inflammation, and diet-related diseases such as diabetes, cardiovascular disease and certain cancers.
That’s why antioxidants are an important part of our diet, controlling the level of oxidative stress in our systems and reducing disease. Fruit and vegetables are a rich source of antioxidants vitamins, minerals, dietary fibre, polyphenols and other beneficial plant compounds that benefit our health in multiple ways. We don’t eat anything close to enough fruit and vegetables. Studies in the US and China show that on average, people eat less than 10% of the recommended intake for better health.
Dietary fibre is also essential for better health and the majority of adults do not eat enough fibre every day. The recommended daily intake is about 25 grams for women and about 32 grams for men, but in Western society most struggle to get even half the amount that we need. We get fibre mostly from fruit, vegetables, whole grains, cereals (oats, bran) and nuts & seeds, beans and legumes.
When we eat fibre it passes through our systems largely undigested and feeds the healthy bacteria living in our gut (sugar feeds the unhealthy bacteria). Research studies around the world are coming closer to understanding the link between our gut microbiota, the complete collection of bacteria, viruses and fungi that live in our gastrointestinal system, and our brain health. Studies have linked Parkinson’s disease, Huntington’s disease, depression, anxiety, ADHD, myalgic encephalomyelitis (ME) and Alzheimer’s disease to an unhealthy balance of bacterial strains living within us.
One of the ways to alter this balance to a healthy level is to eat less sugar and UPFs and eat more fruit, vegetables and whole grains. The traditional Mediterranean diet ticks all the boxes for disease prevention and healthy ageing by way of diet.