Is Alzheimer's really type 3 diabetes? Why your metabolic health in midlife matters

September 22, 2026

Is Alzheimer's really type 3 diabetes? Why your metabolic health in midlife matters

What if looking after our metabolic health in midlife could make a difference to our memory 20 or 30 years from now.

It's a confronting thought, but emerging research into Alzheimer's is revealing something fascinating. The disease may begin with changes in how our brain uses energy, long before we notice problems with our memory.

For decades, Alzheimer's research has focused heavily on amyloid plaques and tau tangles. These abnormal proteins are characteristic features of the disease, but they're not the whole story. Scientists are increasingly investigating the metabolic changes that may contribute to their development, particularly insulin resistance and impaired glucose metabolism.

Some researchers are even calling Alzheimer's type 3 diabetes.

It's not an official diagnosis, and Alzheimer's isn't simply diabetes relocated to the brain. But the term highlights something important: our metabolic health may play a much bigger role in brain health than we previously understood.

And if that's the case, looking after our metabolism in midlife could be one of the ways we help protect our brains for the future.

What's happening to our brain's energy supply?

Our brain is an energy-hungry organ. It makes up only around 2% of our body weight but uses approximately 20% of our body's energy. Most of that fuel comes from glucose.

In Alzheimer's, certain areas of the brain become less efficient at using glucose. This is known as brain glucose hypometabolism, and it can appear years before noticeable memory problems develop.

Insulin does more than regulate our blood sugar. It also helps our brain cells function properly and plays a role in memory, learning and energy use.

When the brain becomes insulin resistant, these processes may be disrupted, contributing to inflammation, cell damage and the build-up of proteins associated with Alzheimer's.

It's not that glucose can no longer enter the brain – most brain glucose uptake doesn't require insulin. Rather, the brain may become less efficient at managing and using its energy.

A 2025 review of 213 studies found growing evidence linking brain insulin resistance and disrupted energy metabolism with Alzheimer's disease. [1]

The science is still developing, but the important point is this: impaired brain energy metabolism may be part of what causes Alzheimer's, rather than simply being a consequence of it.

Why your 40s and 50s could be a critical window

Here's where the research gets really interesting.

A 2025 study of 19,300 people found that changes in how our brains function can begin as early as our mid-40s. Researchers identified insulin resistance as a possible contributor to these changes.

They also found that giving people ketones, an alternative fuel for the brain, temporarily improved brain function, with the greatest benefits seen in those aged 40–59. [2]

While this study didn't prove that ketones can prevent Alzheimer's, it suggests that midlife may be an important window for looking after our brain's energy supply, before more significant changes occur.

That's another good reason to start looking after our metabolic health now, rather than waiting until we're older.

What does blood sugar have to do with Alzheimer's risk?

We already know that type 2 diabetes is associated with an increased risk of dementia, including Alzheimer's. But research suggests that glucose regulation may matter even before someone develops diabetes.

Research suggests that blood glucose levels may affect our risk of dementia, even if we don't have diabetes. A 2013 study of more than 2,000 older adults found that higher average blood sugar was linked to an increased risk of dementia. [3]

A 2025 study also found that people with type 2 diabetes whose long-term blood sugar levels fluctuated more had poorer memory and thinking skills, along with changes in brain structure. This was true even after accounting for their average blood sugar levels. [4]

These findings suggest that keeping our blood sugar well managed and relatively stable may be important for brain health.

While the studies don't prove that blood sugar fluctuations cause Alzheimer's, we know that persistently high blood sugar and insulin resistance can contribute to inflammation and cell damage — processes that may also play a role in the disease.

And that brings us to what we eat.

Could reducing refined carbohydrates help protect our brains?

If you've been following Wholo Foods for a while, you'll know I'm a big believer in reducing excessive refined carbohydrates and added sugars.

Foods made predominantly from refined flours, starches and sugars are often rapidly digested, releasing glucose into our bloodstream. Our bodies respond by producing insulin to help regulate blood sugar.

If we're already insulin resistant, managing that glucose becomes more difficult. Over time, persistently elevated blood glucose and insulin resistance can contribute to metabolic disease.

Reducing refined carbohydrates and choosing foods rich in fibre, protein and healthy fats can help improve glucose regulation (read more here about blood sugar control). For some people, particularly those with insulin resistance or type 2 diabetes, a lower-carbohydrate approach may be beneficial.

That doesn't mean necessarily avoiding carbs, but it does mean choosing carbs that are whole food based like vegetables, whole fruit and legumes which provide valuable nutrients and fibre.

It's about looking at the overall quality of what we eat, rather than relying heavily on refined carbohydrates.

And there's another interesting aspect to this: giving our brain access to an alternative fuel.

What about ketones?

Our brain is a bit like a hybrid engine. It normally runs predominantly on glucose, but it can also use ketones.

Your body makes ketones when it’s using fat instead of glucose for energy. Your body usually gets most of its energy from glucose, a sugar that mainly comes from the carbs in your diet. If you don’t get enough energy from glucose, your body breaks down fats for energy instead. The breakdown releases ketones that travel through your bloodstream. This happens during fasting and when following a low-carb or keto diet.

What's particularly interesting is that the brain's ability to use ketones may remain relatively well preserved even when glucose metabolism is impaired. That's one reason researchers are investigating ketones in relation to brain ageing. [5]

So how can we encourage our bodies to produce more ketones?

One approach is reducing carbohydrate intake. A sufficiently low-carb diet can increase ketone production.

Another option is intermittent fasting or time-restricted eating. Going longer between meals allows insulin levels to fall and your body to start burning stored fat for energy. This can increase ketone production, usually starting after 12 hours of fasting. [6]

Does this mean fasting or following a ketogenic diet can prevent Alzheimer's? We don't know yet. But early research into ketones is promising and gives scientists good reason to investigate further. [2]

In the meantime, reducing refined carbohydrates, looking after our blood sugar so it doesn't spike too high and then drop low too often and extending our overnight fast to at least 12 hours are practical ways to support metabolic health and encourage our bodies to use fat and ketones for energy.

If you take diabetes medication, particularly insulin or medication that can cause low blood sugar, seek medical advice before fasting or significantly restricting carbohydrates. Fasting also isn't appropriate for everyone.

Your metabolic health: four things worth doing now

The encouraging thing is that many of the habits that support metabolic health also support long-term brain health. We don't need to wait for the Alzheimer's prevention trials to recognise the value of looking after our insulin sensitivity, blood glucose and cardiovascular health.

Here are five practical places to start.

1. Eat fewer refined carbohydrates and added sugars. Build your meals around whole foods, with plenty of vegetables, fibre, protein and beneficial fats. If you're insulin resistant, a lower-carbohydrate approach may be helpful.

2. Consider giving yourself longer gaps between meals. Try avoiding snacking and consider time-restricted eating, particularly aiming for a minimum of a 12 hour overnight fast. These approaches can help lower insulin levels between meals and may increase ketone production.

3. Move your body regularly. Exercise helps our muscles take up glucose. A short walk or 30 bodyweight squats within 15-30 minutes after finishing a meal is an easy place to start.

4. Prioritise sleep and manage stress. Poor sleep can worsen insulin resistance, while ongoing stress can make glucose regulation more difficult. Both deserve attention when we're looking after our metabolic health.

Making whole-food eating easier with Wholo Foods

As a nutritionist and health coach, I'm passionate about helping people eat well. But I also know that preparing everything from scratch isn't realistic for most of us!

That's why we make convenient foods using real, minimally processed ingredients.

Our Vitality Wraps are made from fresh carrots, linseeds and avocado oil, providing a fibre-rich, low-carb alternative to traditional flour-based wraps. Our nut-based Amazeballs offer lower-sugar options for your afternoon snack, while our Keto Seeded Crackers help make it easy to eat low carb and enjoy more nuts and seeds.

They're simple ways to include more whole-food ingredients in your day, without relying on refined flours or excessive sugars.

The bottom line: don't wait until you're older to look after your brain

We're still learning about the relationship between Alzheimer's and metabolic health. We don't yet know whether improving insulin sensitivity, following a ketogenic diet or practising intermittent fasting can prevent the disease.

But the emerging research is hinting strongly that it may well be important for our future brain health.

My take-home message? The time to start looking after your brain is now, not when you begin experiencing memory problems.

Eating well, reducing excessive refined carbohydrates, maintaining healthy blood glucose and insulin sensitivity, moving regularly and sleeping well are things we can influence today.

There's no guarantee that any of these will prevent Alzheimer's, but they're still worthwhile investments in our long-term health.

And that's a pretty good reason to start today.

References

1. Atabi F, Moassesfar M, Nakhaie T, et al. (2025). A systematic review on type 3 diabetes: bridging the gap between metabolic dysfunction and Alzheimer's disease. Diabetology & Metabolic Syndrome, 17, 356.

https://doi.org/10.1186/s13098-025-01930-2

2. Antal BB, van Nieuwenhuizen H, Chesebro AG, et al. (2025). Brain aging shows nonlinear transitions, suggesting a midlife "critical window" for metabolic intervention. Proceedings of the National Academy of Sciences, 122(10), e2416433122.

https://doi.org/10.1073/pnas.2416433122

3. Crane PK, Walker R, Hubbard RA, et al. (2013). Glucose levels and risk of dementia. New England Journal of Medicine, 369(6), 540–548.

https://doi.org/10.1056/NEJMoa1215740

4. Lu W, Shen D, Qiu S. (2025). Association between visit-to-visit glucose variability and brain morphology and cognitive function in type 2 diabetes. The Journal of Clinical Endocrinology & Metabolism, 110(12), 3461–3469.

https://doi.org/10.1210/clinem/dgaf228

5. Croteau E, Castellano CA, Fortier M, et al. (2018). A cross-sectional comparison of brain glucose and ketone metabolism in cognitively healthy older adults, mild cognitive impairment and early Alzheimer's disease. Experimental Gerontology, 107, 18–26.

https://doi.org/10.1016/j.exger.2017.07.004

6. de Cabo R, Mattson MP. (2019). Effects of intermittent fasting on health, aging, and disease. New England Journal of Medicine, 381(26), 2541–2551.

https://doi.org/10.1056/NEJMra1905136