Type 3 Diabetes is the Driver of Dementia and Alzheimer's Disease

People that have insulin resistance, in particular those with type 2 diabetes have an increased risk of suffering from Alzheimer's disease estimated to be between 50% and 65% higher.

Researchers have discovered that many type 2 diabetics have deposits of a protein called amyloid beta in their pancreas which is similar to the protein deposits found in the brain tissue of Alzheimer's sufferers.

The biggest diet-related risk factor that everyone in the Paleo world likes to point out for Alzheimer’s is diabetes. People with diabetes are much more likely to develop Alzheimer’s than the general population, and it’s likely that this is a consequence of diabetes itself (not just an association). Diabetes is primarily a disease of glucose (carbohydrate) metabolism, and there’s strong evidence that impaired glucose metabolism in the brain plays a role in the development of Alzheimer’s by depriving cells of energy. If your brain cells are dependent on carbs for energy, but your ability to metabolize carbs is compromised, your brain cells aren’t going to do very well. What’s more, some initial research suggests that ketogenic diets (which provide the brain with fat instead of glucose as fuel) may be helpful as a therapy.

This particular problem even has a name: “Type 3 Diabetes” which is the insulin resistance in the brain associated with Alzheimer’s Disease. (if you need a brush-up on insulin, glucose metabolism, and other related issues, here’s a quick explanation of what insulin is, and here’s an overview of what “glucose tolerance”/”carbohydrate tolerance” actually means and why it’s important.)

Another piece of evidence supporting the “Type 3 Diabetes” theory is that other known risk factors associated with Alzheimer’s are also directly or indirectly connected to impaired glucose metabolism. Risk factors for Alzheimer’s include…

• Sleep apnea (a sleep disorder where the patient wakes up many times during the night; it reduces the benefits of sleeping and deprives the brain of oxygen). Sleep apnea reduces insulin sensitivity and increases the risk of metabolic disorders like diabetes, so it might contribute to Alzheimer’s by messing up glucose metabolism even more.
• Physical inactivity. Regular movement makes for good glucose tolerance; a sedentary lifestyle is one big step towards the opposite, so it’s not surprising that it’s a major risk factor for both diabetes and Alzheimer’s.
• Depression. Insulin metabolism problems may contribute to depression, so depression may be one sign of less-than-optimal insulin metabolism.
• Obesity. Obesity and diabetes often go hand in hand – they’re both associated with problems metabolizing carbohydrates.
• Smoking. Smoking impairs insulin sensitivity, and quitting improves it.

In other words, a lot of the risk factors for Alzheimer’s tie into insulin and glucose metabolism one way or another. The connection with diabetes, plus the tentative research showing a benefit for ketogenic diets, leads a lot of people to conclude that carbs “cause Alzheimer’s” and that a ketogenic diet is the only way to prevent it. But as usual, the simplification doesn’t hold up under closer scrutiny.

“Carbs” as a group means nothing unless you separate “carbohydrate overload in the context of an inflammatory and obesogenic diet full of gut irritants” from “carbohydrates from whole foods in the context of an anti-inflammatory diet low in gut irritants.” The first is associated with Alzheimer’s; the second is not. An inflammatory, obesogenic diet that also happens to be high in carbs may contribute to Alzheimer’s (among other problems), and a lower-carb diet may be helpful as a treatment, but that doesn’t mean that whole-food carbs in an anti-inflammatory context are dangerous.

But wait a minute, where’s all the talk about inflammation coming from?

Insulin is a hormone produced in the pancreas. In healthy, non-diabetic, non-obese people, insulin is responsible for important things like…

• Muscle gain: as every bodybuilder knows, insulin is anabolic. It helps your body turn dietary protein into muscle.

• Blood sugar control and energy storage: insulin controls blood sugar within a tight range. This is important: it’s very dangerous to have too many simple sugars just hanging out in your bloodstream.

• Satiety: insulin helps make you feel full after a meal. Yes, full. Not hungry. If eating refined carbs makes you ravenous, it’s because of the blood sugar highs and crashes, not because your body released insulin in response.

• Bone strength: insulin helps maintain bone mass and even stimulate new bone growth.

That’s how insulin works in healthy people. Many people in the US today have diabetes or some degree of impaired insulin metabolism, and for those people, insulin metabolism is very different. In diabetes, the pancreas either don’t produce insulin at all (Type 1 Diabetes) or the rest of the body doesn’t respond properly to the insulin they do produce (Type 2 Diabetes/metabolic syndrome). This obviously means that insulin works differently in diabetes, but diabetes is not what this particular article is about.

So with that said, here’s a look at how insulin works, what insulin sensitivity and insulin resistance are, what they have to do with body weight, and why metabolic health doesn’t necessarily mean keeping insulin as low as possible. A lot of the evidence is taken from this review and this one, both free for anyone to read.

The opposite of insulin sensitivity is insulin resistance. In insulin resistance, your body produces insulin normally, but doesn’t use it properly, and the whole delicate balance of blood sugar regulation, fat storage, and fat burning breaks down. This causes all kinds of problems, including chronically high insulin, and it can cause weight gain because “fat-storing” mode is always on, and “fat-burning” mode is always off.

This is what most people are probably thinking of when they say things like “high insulin levels cause weight gain,” but insulin resistance is not the way insulin works in healthy people. It’s a very complicated problem, with many different causes. Just to name a few:

• Chronically high fructose (sugar) consumption or overconsumption of simple carbohydrates in general. Panicking over fruit is counterproductive and unnecessary, but sugar-sweetened soft drinks are probably a bad idea.
• Unhealthy gut flora. Was there ever a health problem where the gut flora weren’t involved? Gut dysbiosis contributes to insulin resistance in various ways.
• Chronic stress (including but not limited to sleep deprivation, starvation, psychological stress, and social isolation).
• Hormone imbalances. For example, women with PCOS often have insulin resistance or metabolic syndrome.
• Some medications include beta-blockers, steroids, and some diuretics.
• Obesity, especially abdominal obesity (an apple-shaped silhouette as opposed to pear-shaped).
• All other things being equal, women also have generally better insulin sensitivity than men.

(Also, just as a note, it’s commonly repeated that eating saturated fat causes insulin resistance. This may be true in rats, but it doesn’t pan out in human trials. You can read an explanation here.)