Some Researchers Call Alzheimer’s “Type 3 Diabetes”. Here Is Why.

By Tina Chagoury, Clinical Dietitian · 5 min read · 2026-11-09

The phrase is provocative and it points at something real. Insulin resistance does not stop at the neck.

You may have heard Alzheimer's described as type 3 diabetes. It is a provocative phrase, it is not an official diagnostic category, and it points at something genuinely important.

What the phrase is describing

The brain uses an enormous amount of glucose, and it has its own insulin signalling.

In insulin resistance, cells across the body stop responding properly to insulin. That does not stop at the neck. Brain cells can become less responsive too, which means less efficient glucose uptake in an organ that is exceptionally dependent on it.

Researchers observing this pattern of impaired insulin signalling in the brain, alongside the changes seen in Alzheimer's disease, began using the term.

What is genuinely established, and what is not

Established: insulin resistance and type 2 diabetes are associated with an increased risk of cognitive decline and dementia. That association is consistent across a large body of research.

Also established: chronic inflammation and vascular damage, both of which accompany long term blood sugar dysregulation, contribute to cognitive decline.

Not established: that Alzheimer's is simply diabetes of the brain, or that managing blood sugar prevents it. The disease is multifactorial and includes genetic factors entirely outside dietary control.

I state the boundary clearly because this is an area where fear sells easily.

Why I still think it matters enormously

Because the modifiable part is genuinely modifiable, and the window is decades long.

A heart attack does not happen suddenly. It is the accumulated result of years of blood sugar dysregulation. The same logic of accumulation applies to vascular and metabolic contributions to cognitive decline.

Which means the work done in your forties matters for outcomes in your seventies, and it is the same work that improves how you feel next month.

The short term version you can actually feel

You do not need to wait decades to observe the relationship.

Brain fog is one of the classic symptoms of unstable blood sugar. Losing the ability to concentrate for long stretches. Losing the ability to multitask. An attention span that has become very short.

If your fog is worse in the afternoon, after a carbohydrate heavy lunch, you are watching this mechanism operate in real time.

What to do

The interventions are the same ones that address everything else, which is the useful part.

• Protein within the first hour of waking, and at every meal
• Three structured meals, no all day grazing, so insulin can come back down
• Carbohydrate eaten with protein, fat and fibre, never alone
• A ten minute walk after eating
• Resistance training, which improves insulin sensitivity through a pathway that does not require insulin at all, and which has its own independent associations with cognitive outcomes
• Sleep, at consistent times. This is where the brain performs its own clearance processes.
• Reduce the inflammatory load
• Correct deficiencies, particularly vitamin D, B12 and iron, all of which affect cognition and all of which are common

What to test

Fasting glucose and fasting insulin together, so HOMA-IR can be calculated. HbA1c. A full lipid panel. Inflammatory markers. Vitamin D, B12 and ferritin.

Fasting insulin is the one most often left off, and it is the one that identifies the problem years before glucose becomes abnormal. That gap is exactly where the opportunity is.

This article is nutrition education, not medical advice. Cognitive concerns should be assessed by a doctor.

Tina Chagoury is a licensed clinical dietitian specialising in women's hormonal health and metabolism, and the creator of the Hormone Reset Method™. Learn more and start here.