People suffering from Alzheimer’s disease could also face an increased risk of developing type 2 diabetes, according to a new study published in the journal Alzheimer’s and Dementia. Based on their findings, the researchers suggest that people suffering from dementia, or with a family history of the condition, should be particularly careful to avoid a high-fat diet.

Type 2 diabetes occurs when the body is unable to efficiently use insulin, a hormone produced in the pancreas that facilitates the absorption of glucose from the blood into body cells. When this occurs, blood glucose levels become unregulated, potentially leading to a range of dangerous effects such as kidney failure.

Studies have shown that eating a high-fat or high-sugar diet increases the chance of developing the disorder, although a range of factors – such as genetics or other health conditions – also have a say in determining a person’s likelihood of suffering from diabetes.

Prior studies have indicated that there may be a connection between Alzheimer’s and diabetes, but this has never been confirmed. What is known, however, is that insulin acts as a messenger in a part of the brain called the hypothalamus, which regulates the body’s overall metabolism, controlling the rate at which glucose, fats and amino acids (the building blocks of proteins) are broken down to release energy.

The study authors therefore suggest that Alzheimer’s disease somehow causes the hypothalamus to become insulin resistant, meaning it loses the ability to respond to insulin. This, they propose, disrupts a number of metabolic processes throughout the body, causing overall insulin resistance and resulting in type 2 diabetes.

^{Diabetes can be regulated by a combination of eating carefully and insulin injections. Robert Przybysz/Shutterstock}

To test this, they genetically engineered mice to develop Alzheimer’s-related symptoms early in life, some of which were fed a high-fat diet while the others were fed “a standard chow.” At the same time, they also ran the experiment with regular mice, in order to get an idea of how diet influences those affected by Alzheimer’s compared to those who are not.

Results showed that the mice with dementia-like characteristics suffered a greater degree of “metabolic dysregulation” than the healthy mice, and that this was particularly severe in those that were fed a high-fat diet.

Commenting on these “compelling and unexpected results,” study co-author Sam Gandy said that this pioneering study into the connection between Alzheimer’s and diabetes provides a “complete re-evaluation of how these diseases interact."

To confirm that this connection is driven by insulin resistance in the hypothalamus, the researchers looked for other tell-tale signs that this part of the brain had ceased to perform its metabolic functions. For instance, since insulin signaling in the hypothalamus regulates the breakdown of branched chain amino acids (BCAA) to release energy, the study authors decided to measure levels of BCAA in the blood.

In doing so, they found that mice with Alzheimer’s had much higher blood BCAA levels, particularly when fed a high-fat diet. As such, they conclude that Alzheimer’s does indeed cause insulin resistance in the brains of mice, leading to overall metabolic dysregulation, and potentially culminating in type 2 diabetes.

While more work needs to be done to determine how Alzheimer’s generates insulin resistance in the hypothalamus – and, indeed, whether or not this also occurs in humans – the findings provide compelling evidence as to the risks of a high-fat diet, particularly in those at risk from dementia.