Metabolic flexibility and brain health: what it means

Quick answer

Metabolic flexibility is the ability to switch between glucose, fat and ketones for energy, depending on what is available. The brain can use ketones as well as glucose. At CogMission, we think this flexibility may be one important piece of brain health, alongside vascular health, inflammation, sleep, activity, hormones, nutrient status and genetics.

When we talk about protecting the brain as we age, we often think about sleep, exercise, genetics and keeping mentally active.

But there’s another question worth asking:

How well can your brain access fuel?

Most of us think of glucose as the brain’s main energy source. But the brain can also use ketones: an alternative fuel produced when insulin falls and the body begins using more stored fat for energy.

The ability to move between these different fuel sources is called metabolic flexibility, and it may be an important piece of the brain-health puzzle.

The problem can start before blood sugar rises

One of the most interesting points from Dorian Greenow’s presentation on nutritional ketosis at Integrative Personalised Medicine (IPM) Congress 2026 was that insulin resistance can develop while blood glucose still appears normal.

As cells become less responsive to insulin, the pancreas compensates by producing more of it. For a while, that extra insulin can keep glucose within the normal range.

So a normal fasting glucose or HbA1c (average blood sugar over about three months) doesn’t necessarily tell us the whole story. Hyperinsulinaemia can precede the loss of glucose control by years.

This matters because metabolic dysfunction isn’t just associated with diabetes. The presentation also highlights cardiovascular disease, fatty liver disease and cognitive decline.

Your brain has another fuel

When insulin and carbohydrate availability fall sufficiently, through fasting, exercise or carbohydrate restriction, for example, the body can increase fat burning and produce ketones.

And the brain can use them.

Ketones cross the blood-brain barrier and provide an alternative energy source; the presentation also highlights that astrocytes within the brain can produce ketones locally.

This doesn’t mean glucose is bad, or that everyone needs to follow a ketogenic diet.

What interests us is metabolic flexibility: the ability to switch between glucose, fat and ketones according to what is available.

Think of it as having more than one gear.

So, should we all go keto?

No.

Carbohydrate tolerance varies enormously according to metabolic health, activity, genetics and health history.

For one person, reducing refined carbohydrates may be enough. Another may benefit from changing meal timing, increasing exercise or improving muscle mass and insulin sensitivity. In selected circumstances, nutritional ketosis may be used more deliberately.

The point isn’t to chase ketones.

It is to understand what your metabolism is doing.

And today, we have increasingly useful ways of doing that.

We can look at glucose alongside insulin rather than glucose alone. Continuous glucose monitoring can show individual responses to meals, exercise, stress and sleep. And when nutritional ketosis is being used therapeutically, blood beta-hydroxybutyrate (BHB) provides an objective way of measuring whether ketosis is actually occurring.

That allows us to move away from:

“This diet should work.”

towards:

“What is actually happening in your body?”

What does this mean for brain health?

At CogMission, we’re not interested in putting everyone on the same diet.

We’re interested in understanding the metabolic environment in which the brain is operating.

Is insulin already elevated despite normal glucose? How stable is glucose throughout the day? How does an individual respond to carbohydrate? Can the body readily switch from glucose towards fat and ketones when appropriate?

Brain health is influenced by far more than metabolism alone – vascular health, inflammation, sleep, physical activity, hormones, nutrient status and genetics all matter.

But metabolic health is an important part of that bigger picture.

So perhaps the most useful question isn’t:

“Should I go keto?”

It’s:

“How metabolically flexible am I?”

Common questions

Can the brain use ketones for energy?

Yes. Ketones are produced when insulin falls and the body uses more stored fat for energy. They cross the blood-brain barrier and provide an alternative fuel for the brain. Dorian Greenow’s presentation at IPM Congress 2026 also highlights that astrocytes in the brain can produce ketones locally. This does not mean glucose is bad.

Can you have insulin resistance with normal blood sugar?

According to Dorian Greenow’s presentation at IPM Congress 2026, insulin resistance can develop while blood glucose still appears normal. The pancreas makes more insulin to compensate, which can keep glucose in range for a while. So a normal fasting glucose or HbA1c may not tell the whole story.

Should everyone follow a keto diet for brain health?

No. Carbohydrate tolerance varies with metabolic health, activity, genetics and health history. For some people, reducing refined carbohydrates may be enough. Others may benefit from changing meal timing, exercising more or improving muscle mass and insulin sensitivity. Nutritional ketosis may be used more deliberately in selected circumstances.