Why Your Brain Feels Foggy, Slow, or Overwhelmed: The Metabolic Story No One Is Telling

Why do so many people today struggle with brain fog, poor focus, memory lapses, slow thinking, irritability, emotional sensitivity, or difficulty switching between tasks?

Two important scientific pieces—Picard’s chapter on brain energy vulnerability and Jamadar et al.’s 2025 review on the metabolic costs of cognition—provide the clearest explanation yet:

👉 Cognitive dysfunction is, at its core, an energy problem.

👉 When the brain cannot produce or access enough usable energy, thinking becomes harder.

👉 This metabolic bottleneck—glucose dependence + limited reserves—makes the brain uniquely fragile.

And surprisingly, neither paper discusses one of the most promising solutions: ketones as an alternative fuel when glucose metabolism breaks down.

Let’s unpack what this means for real-life symptoms.

The Brain Is the Body’s Most Energy-Hungry Organ—with the Smallest Fuel Tank

Both Picard and Jamadar emphasize the same fundamental point:

The brain consumes 20% of your resting energy but stores almost no fuel.

It must:

• run thousands of neural networks

• maintain billions of ion channels

• recycle neurotransmitters

• keep memories active

• coordinate emotion, attention, decisions, movement

—all in real time, from moment to moment.

This high “metabolic idle” means:

**Most of your brain energy is spent just keeping the lights on.

Not thinking. Not learning. Just maintaining function.**

That’s why even mild interruptions in energy supply can cause noticeable symptoms.

Why Cognitive Symptoms Appear When Brain Energy Falters

Here is what Picard and Jamadar help us understand:

1. Brain fog (the inability to think clearly)

Foggy thinking happens when the brain’s networks can’t maintain stable firing because ATP availability drops. Neurons can’t keep up with demand, so the clarity of thought collapses.

2. Difficulty focusing or sustaining attention

Attention networks—especially frontal and parietal hubs—are metabolically expensive. When energy is low, the brain literally cannot afford their activation.

3. Memory lapses and short-term retention problems

The hippocampus is extremely glucose-dependent.In insulin resistance or stress, glucose delivery drops → memory falters.

4. Emotional volatility or irritability

Emotion regulation requires frontal control networks. Low energy impairs their ability to “hold the line.”

5. Mental fatigue after small mental tasks

Switching between tasks is one of the most energy-intensive operations in the brain. Jamadar shows that this “network switching cost” is a major consumer of glucose. When energy is scarce, switching feels exhausting.

6. Slow processing or delayed responses

Neurons fire more slowly and less synchronously under glucose shortage. This shows up as slower cognition.

7. Feeling overwhelmed easily

The ability to integrate information across multiple networks is energy-demanding.Low energy → early overwhelm.

These are not psychological failures. These are metabolic symptoms.

Why Are So Many Brains Energy-Compromised Today?

Picard and Jamadar highlight the culprits:

✔ Chronic stress

Stress forces the brain into high-energy states repeatedly without adequate recovery.

✔ Insulin resistance

The brain becomes less able to use glucose—the primary fuel it depends on.

✔ Glucose variability (peaks and crashes)

Disrupts stable ATP production.

✔ Inflammation

Increases metabolic cost while reducing efficiency.

✔ Aging and mitochondrial decline

Lower ATP production, higher oxidative burden.

✔ Nutrient insufficiency

Reduces the brain’s ability to generate and regulate energy.

And this is where the story gets interesting.

Both Papers Describe the Problem Perfectly… but Miss the Solution

Despite a 12-page review on glucose metabolism, ketones aren’t mentioned once.

This is surprising, because ketones:

• enter the brain independently of insulin

• bypass impaired glucose transport

• produce ATP more efficiently

• reduce oxidative stress

• support mitochondrial function

• improve cognitive performance in insulin resistance

• directly rescue the same energy bottleneck described in the review

In other words:

👉 Ketones provide fuel when the brain cannot use glucose properly.

👉 They directly counteract the metabolic vulnerabilities both authors describe.

👉 They are one of the most practical tools for restoring cognitive function.

Ignoring ketones means missing the most immediately actionable way to support brain energy—and therefore support cognition.

The ERM Perspective: Energy Mismatch → Cognitive Mismatch

Your brain symptoms are often early warning signs of what I call Exposure-Related Malnutrition (ERM): a mismatch between energetic demand and metabolic supply, driven by chronic stress, poor recovery, and impaired substrate availability.

From this lens:

• Brain fog = energy deficit

• Overwhelm = network overextension

• Poor focus = insufficient ATP at hubs

• Memory lapses = hippocampal glucose bottleneck

• Emotional reactivity = impaired frontal control

• Fatigue = network switching cost with no metabolic buffer

This is not “laziness,” “aging,” or “stress sensitivity.”

This is bioenergetic insufficiency.

And here’s the hopeful part:

**Cognition improves when brain energy improves.

Improve the fuel → improve the function.**

A More Complete View: Glucose + Ketones + Recovery

A modern, practical framework for cognitive health must include:

✔ Improving glucose handling

✔ Reducing insulin resistance

✔ Supporting mitochondrial function

✔ Reducing inflammation

✔ Ensuring nutrient sufficiency

✔ Enhancing recovery and circadian alignment

✔ Allowing ketones as an alternative energy pathway

Because when the brain’s energy supply becomes more stable……cognitive improvement becomes possible again.

Rae, C. D., Barros, L. F., Behnke, A., Goyal, M. S., Herculano-Houzel, S., Peleg-Raibstein, D., Picard, M., Rothman, D., Vernon, A. C., & Sarnyai, Z. (2025). Brain energy constraints and vulnerability. In D. Öngür & J. M. Ford (Eds.), Metabolic neuropsychiatry (Strüngmann Forum Reports, pp. 29–55). Springer. https://doi.org/10.1007/978-3-032-05630-6_3

Jamadar, S. D., Behler, A., Deery, H., & Breakspear, M. (2025). The metabolic costs of cognition. Trends in Cognitive Sciences, 29(6), 541–555. https://doi.org/10.1016/j.tics.2024.11.010