The Western Diet Linked to Alzheimer’s

In this Article (Index)

• Alzheimer's Disease
• The Disease: changes, symptoms, risk
• Causes: Genetics
• Junk food can increase Alzheimer's risk

Alzheimer's Disease

Around 6.9 million older Americans over the age of 65 are currently living with Alzheimer's disease. This number is expected to duplicate (13.8 million) by 2060. In 2021, over 119,000 people died of Alzheimer's in the U.S, and it is the fifth major cause of death among those 65 and older having grown 140% between 2000 and 2021. (2)

In most cases, Alzheimer's disease develops when people are 65 or older, with only 10% of the cases taking place at a younger age. The risk increases with age. From 1 in 13 people between 65 and 84, to 1 in 3 after 85. (3)

The disease is the most common cause of dementia, making up between 60% and 80% of the total cases.

The Disease: changes, symptoms, risk

A summary of Alzheimer's disease and its symptoms. (2)

Brain Changes

Alzheimers disease causes the accumulation of a protein called beta-amyloid (β-amyloid) outside of the brain's nervous cells or neurons and twisted strands of another protein called protein tau inside the neurons. This causes inflammation and damage to the brain tissue, and it kills the neurons.

Symptoms

The symptoms appear gradually and worsen, affecting memory and mood. They include loss of memory and difficulty remembering names, events, places, and conversations. They also include depression, apathy, and confusion. Communication issues and changes in behavior are also present. Impaired mobility (walking, speaking, and swallowing) are also symptoms.

Causes: Genetics

The strongest cause for the late onset of Alzheimer's disease is a genetic mutation in a gene that codes for a protein, Apolipoprotein E.

Apolipoprotein E helps transport fats like cholesterol within tissues, including the brain. It is coded by a gene called APOE, which comes in three different genetic variants or alleles named APOEΕ2, APOEΕ3, and APOEΕ4.

• APOE Ε2. Could provide some protection against Alzheimer's. If the disease appears in a person with this allele, it does so at a later age. Its global prevalence is 5% to 10% and is absent in Native Americans and Australian Aboriginals.
• APOE Ε3, the most common allele is neutral regarding the disease as it does not increase or decrease the risk.
• APOE Ε4 increases the risk of Alzheimer's and can cause it to appear at a younger age. 15% to 25% of the population have this allele.

Each person inherits one copy of the APOE gene from their biological parents meaning that there are six possible combinations of these three variants: 2/2, 2/3, 2/4, 3/3, 3/4, and 4/4.
The last combination is the "two alleles" one, which heightens the risk. Two percent to five percent of the population carry two copies of it. Carrying two of these alleles can increase the risk of developing Alzheimer's disease by the age of 75 ten to thirtyfold compared to those who don't carry the two copies.

Roughly 1 in 4 of the population carries one copy of the APOE Ε4 allele which is linked to a higher susceptibility to coronary artery disease, vascular dementia, Lewy Body disease, and Alzheimer's Disease. However, its role in Alzheimer's disease hasn't yet been clearly understood.

Many of those with the APOE Ε4 allele may never develop the disease. (4)

Exposure to the unhealthy Western diet and modern longer lifespans could have increased the risk for those carrying this APOE Ε4 allele. This is suggested by the lower prevalence of Alzheimer's in Sub-Saharan Africans that carry this allele and the opposite effect in African Americans exposed to the Western diet and lifestyle.

A high-fat diet also increases the risk of dementia and Alzheimer's. Women also have a higher risk of getting the disease at a younger age and experience a faster memory decline than men.

Junk food can increase Alzheimer's risk

Research published in November 2024 (1) by a team from Northeastern University revealed that what one eats has a greater impact than genetics on the chances of getting Alzheimer's disease.

The study fed rats a typical junk food diet high in fat, carbohydrates (mostly added sugars), and cholesterol. They used two types of rats. One group had the APOE Ε4 gene that increased their risk of Alzheimer's, while the other rats didn't carry the APOE Ε4. The authors expected the rats with the APOE Ε4 gene to get the disease in a larger proportion than the rats without this variant.

However, the results were totally unexpected, "the genetic risk was overshadowed by the diet." The rats without the APOE Ε4 gene performed far worse in cognitive tests than the ones with it.
This was interpreted as a link between a poor diet and an increased risk for Alzheimer's, far greater than the susceptibility caused by carrying the APOE Ε4 allele.

Details of the Study

Male and female rats were fed a diet that was high in fat and sugar: 48.5% carbohydrates (34% sucrose), 21.2% fat, 17.3% protein, and 0.2% cholesterol. The study lasted four months, equivalent to 8.7 human years, which added an "aging" effect to the trial.

Exposed to an unhealthy "Western" diet, the rats with the APOE Ε4 allele were expected to get Alzheimer's at a higher rate than the rats that didn't carry that variant. But "there was no evidence of cognitive dysfunction or functional connectivity in female or male APOE Ε4 allele carriers." Instead, the most affected by the high-fat & high-sugar diet were the male rats that lacked the APOE Ε4 allele. It had no impact on the female rats without the allele.