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Can You Eat Your Way to Dementia?

An unhealthy diet not only is bad for your waistline--it may also trigger Alzheimer's disease
Reader's Digest
February 2013
p. 116

New findings show that insulin resistance is linked to loss of cognition and memory
Research on rats is revealing a connection between Alzheimer's disease and diabetes symptoms.
When given a diabetic drug that interferes with the brain's ability to respond to insulin, the rats could not remember where they were and could not navigate their way around.
Poor sensitivity to insulin typically is associated with Type 2 diabetes and it plays a key role in brain signaling.

Some researchers are investigating whether Alzheimer's disease may be a version of diabetes that targets the brain, and have renamed it Type 3 diabetes.
Since sugary, calories foods have been known to impair the body's response to insulin, the question becomes whether a poor diet poisons the brain.

The role of beta-amyloid
For more than a century, scientists blamed beta-amyloid plaques that collected in the brain as the cause of Alzheimer's disease.
Beta-amyloid is a portion of a larger protein that helps form brain cell membranes, and is thought to carry out important functions that include: fighting microbes, transporting cholesterol, and regulating certain genes.
It is a mystery what causes the protein to release toxic fragments that clump into Alzheimer's plaques; the new research seeks to determine if a diabetes-like illness is the trigger.

The role of insulin
In the past, insulin was considered the regulation of blood sugar--signalling muscle, liver, and fat cells to extract sugar from the blood and use it for energy or to store it as fat.
It now is known that the hormone is a master multitasker.
In the brain, insulin takes up glucose for energy and regulates the neurotransmitters necessary for memory and learning.
Insulin also promotes plasticity--the process by which neurons make new connections.
Insulin also is important for blood vessel functions, the transporters that supply the brain with oxygen and glucose.

Reducing the level of insulin in the brain immediately impairs cognition.
Spatial memory is especially affected when insulin uptake is blocked in the hippocampus.
A boost of insulin improves functioning.

Developing brain diabetes
When binges of fatty or sugary food are consumed, insulin levels spike repeatedly.
Muscle, liver, and fat cells cease responding to the hormone and no longer absorb excess glucose and fat in the blood.
In response, the pancreas works overtime to make more insulin to control the glucose, resulting in high levels of both insulin and glucose.
The constantly high levels of insulin overwhelm the brain, and it becomes less responsive to the signaling hormone.
This impairs the ability to think and form memories, then leads to permanent neural damage.
It has been confirmed that a disrupted insulin system can lead to Alzheimer's symptoms.
Other research shows that triggering diabetes in rabbits creates brain changes.

Further investigation confirms that the brains of people with Alzheimer's disease are insulin resistant; insulin signaling becomes paralyzed.
Insulin and beta-amyloid are both broken down by the same enzyme.
Normally, the enzyme can handle both, but if too much insulin is present, the enzyme is overwhelmed and the beta-amyloid is neglected and begins to accumulate--possibly into the toxic plaques that kill brain cells.
It has been found that clusters of the toxic beta-amyloids attack and destroy brain tissue covered in insulin receptors; the result is immediate cognitive impairment.
The insulin resistance encourages cells to make addition beta-amyloid, which harms more brain cells--triggering a vicious cycle.

Diabetes in the United States
This result of this research is of concern, because in the United States 19 million people have been diagnosed with diabetes, and 79 million are considered pre-diabetic,showing signs of insulin resistance.
Even if a person does not develop diabetes, an unhealthy diet may set the stage for brain degeneration.

A therapy in which insulin is delivered to the brain through the nose shows initial promise.
The glucose metabolism in these patients improved, and memory and attention span were increased.

Maintaining a healthy diet and weight control seems to be a path to ward off cognitive degeneration.
Restricting harmful fats and sweet foods may help reduce Alzheimer's disease.
Increasing omega-3 fatty acid in the diet may help the brain manage insulin efficiently.
Exercise can promote the body to overcome insulin resistance; regular physical activity has been shown to reduce the risk of Alzheimer's disease by 40%

Type 1 diabetes.
Only 5% of those with diabetes have Type 1, which typically is diagnosed in children and young adults.
The body attacks the insulin-producing cells in the pancreas--making it unable to regulate blood sugar.
Insulin therapy is needed for these patients to survive.

Type 2 diabetes
This is the most common.
Either the pancreas does not produce insulin--or the muscle, liver, and fat cells ignore insulin.
This leads to high blood sugar levels and increased risks of heart disease, stroke, blindness, nerve damages, and amputation.

Type 3 diabetes
This new category refers to Alzheimer's disease,which may arise when brain tissue becomes insulin resistant.
It is similar to Type 2 diabetes, but primarily targets the brain.


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