In Depth

Sugar and Alzheimer’s disease

Alzheimer’s disease is a terrible problem in modern society. Alzheimer’s and dementia became the leading cause of death in England and Wales in 2015, and rates are continuing to increase. Improvements in diagnosis have played a role in this, but there is another reason that the number of Alzheimer’s cases is on the rise.

Many of the diseases of the modern age, such as diabetes and cancer, have a metabolic component, meaning metabolism is at least partly responsible. Alzheimer’s is no different. The purpose of this article is to explore the metabolic components of Alzheimer’s, and how diet can play a role in these.

What is Alzheimer’s disease?

Alzheimer’s disease is the most common form of dementia, and results in progressive loss of neurons (brain cells) and synapses (the junctions between those brain cells). This causes cognitive decline which worsens over time. Learning and memory are affected by the disease as an early symptom, with more long-term memories being affected as the disease progresses.

Though all forms of dementia cause cognitive decline, Alzheimer’s disease in particular is characterised by the presence of two abnormal structures in the brain: beta amyloid plaques and neurofibrillary tangles. Accumulation of beta amyloid plaques is worsened by certain genes, such as ApoE4, which worsen the risk of acquiring Alzheimer’s at an earlier age. Removal of beta amyloid has long been a focus of Alzheimer’s research, but has yielded no positive results. It is thought that this is because the plaques are merely a symptom, so their removal is not helpful unless the underlying causes of the disease are addressed.

Glucose and insulin in Alzheimer’s disease

There are many factors at play in Alzheimer’s disease, and different factors can contribute to varying degrees in different individuals. This is one of the reasons Alzheimer’s is so hard to treat. In his book ‘The End of Alzheimer’s’, Dr Dale Bredesen states that 36 contributing factors have been identified so far, and more are likely to follow. He explains that “high insulin and high glucose are two of the most important risk factors for Alzheimer’s disease”, labelling one of the subtypes of Alzheimer’s as ‘glucotoxic’. So how are insulin and blood glucose involved?

Firstly, having chronically high blood glucose levels leads to increased production of advanced glycation end-products (AGEs), which are proteins and lipids that have been damaged by attachment to sugar. HbA1c is a measure of how much glucose is attached to the haemoglobin of your red blood cells, and so, is a measure of how many AGEs are being produced in the blood. AGEs cause damage to the brain in a number of ways, by promoting inflammation, oxidative stress and direct damage to the brain’s blood vessels.

Secondly, after insulin has done its job allowing glucose to enter cells, it is degraded by the aptly named ‘insulin degrading enzyme’ (IDE). However, IDE also degrades amyloid in the brain, when it is not busy working on insulin. The more insulin that is released into the blood, and the more often this occurs, the less spare time IDE has to remove amyloid from the brain. This means that eating refined carbohydrates and sugar often, especially before bedtime when the brain does its housekeeping, may be contributing to Alzheimer’s disease in the long term, by allowing amyloid to accumulate in the brain at a faster rate.

Thirdly, in addition to its roles in glucose metabolism and fat storage, insulin is actually an important survival signal for neurons. When an individual becomes insulin resistant, by having inappropriately raised levels in the long-term, insulin no longer performs this role as effectively. This means that, in addition to contributing to metabolic syndrome and type 2 diabetes, insulin resistance also contributes to the neuronal death seen in Alzheimer’s.

Sugar: a metabolic poison?

So, high blood glucose and insulin levels can increase the risk of developing Alzheimer’s disease, but what changes can we make to our diet to combat this?

Of the three macronutrients, carbohydrate, protein and fat, carbs have the largest effect on insulin response, with protein’s effect being moderate and fat’s effect being almost non-existent. Not all carbs are equal in causing an insulin response either; refined carbs (such as those in white bread, pastries and other processed foods) are rapidly absorbed and cause a larger, faster insulin response than do the natural, complex carbs found in green vegetables. Sugar in particular causes a very rapid insulin response, and is added to most of the packaged foods we buy in the supermarket, from peanut butter to cereal bars and even bread.

A diet that is high in sugar and refined carbohydrates is one that keeps on generating high blood glucose, stimulating high insulin levels and provoking insulin resistance. This situation of metabolic dysfunction is what contributes to Alzheimer’s disease. Likewise, a diet low in sugar allows for better insulin sensitivity, meaning insulin can perform its jobs in the correct manner. As sugar is the main dietary driver of metabolic issues, it is arguably the most important thing to cut down on to prevent any disease with a metabolic component, including Alzheimer’s.

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