⭑ Brain insulin resistant starts at 40 ✔ Starves your brain neurons of energy
⭑ Brain insulin resistance happens without type 2 diabetes ✔ Don’t be complacent
⭑ How our modern diet drives brain insulin resistance ✔ And what to eat instead
⭑ This exercise will help your brain health ✔ At home

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Hello,

I trust you are well and active.

As I happened last week, I stumbled upon another theme which I decided to fors on the entire newsletter - neuronal insulin resistance. I'd never heard of this. It's important we know about it.

Item #1 explains how neural insulin resistance results in our brain cells struggling for fuel - carbohydrates from the blood. This causes them to deteriorate and hence function poorly.

What's also surprising is that neural insulin resistance is not directly caused by late onset type 2 diabetes (metabolic insulin resistance), see item #2.

And on the theme of brain health I think it is important to know about the role of gut in regulating our brain health, which is item #3.

Then, in item #4, I suggest an at-home resistance band exercise which is know to have a positive effect on your brain health when done consistently.
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01 Brain Aging's Critical Midlife Window - 40 to 60

We often think about brain aging as a slow, gradual decline that becomes noticeable in our later years. But new, surprising research from the Proceedings of the National Academy of Sciences (PNAS), published in March 2025, is challenging this notion.

This groundbreaking study reveals that brain aging doesn't follow a linear path; instead, it shows non-linear transitions, with a distinct "critical window" for metabolic intervention emerging in midlife, specifically between ages 40 and 60.

The research analysed functional MRI data from nearly 20,000 participants, discovered that brain networks begin to destabilize consistently around the mid-40s.

⇒ What's even more revealing is that this destabilization coincides with increased insulin resistance in the brain.

We all know about bodily insulin resistance linked to type 2 diabetes, but the idea of neuronal insulin resistance driving early brain aging is a profound insight.

Lead author Dr. Lilianne Mujica-Parodi explains that during this midlife window, neurons are metabolically stressed, struggling for fuel, but not yet irreversibly damaged. The concept of a "midlife brain energy crisis" suggests that ages 40-60 represent a critical window where neuronal insulin sensitivity begins to decline, potentially setting the stage for later cognitive dysfunction.

What this means for you: Here's the kicker: an interventional study on 101 participants showed that administering ketones, an alternative fuel source that bypasses insulin resistance, effectively reversed these brain aging effects.

The beneficial effects were maximized in participants aged 40 to 59, suggesting that interventions aimed at improving brain metabolism during this "bend before the break" period could be incredibly powerful in preventing cognitive decline later in life.

Here's why ketones work in feeding our neurons: Our body, including our brain, primarily seeks glucose as it's an easy and readily available fuel. However, if glucose is scarce (because we're eating very few carbohydrates) or if our cells, including brain cells, struggle to use glucose effectively (which happens in insulin resistance), then the body will switch to burning fat and generating ketones as an alternative fuel.

Instead of jumping straight into a strict keto diet (which can be a big change for most), you can start by:

1. Time-Restricted Eating: Begin with TRE, perhaps 12-14 hours of fasting daily. Even 2 days a week can be beneficial for getting started.
2. Gradual Carb Reduction: Focus on reducing refined carbohydrates and added sugars first (sodas, pastries, white bread, pasta). Replace them with whole, unprocessed foods like non-starchy vegetables, healthy fats, and quality proteins.
3. Increase Healthy Fats: Incorporate more healthy fats (avocado, olive oil, nuts, seeds, fatty fish) into your diet. These are satiating and provide the fuel source your body would shift to.

⇒ You CAN act to reduce cognitive decline before too much damage is done.

Related: ​​Too Much Omega-6 Can Harm Us, Unless We Eat More Omega-3​​​​​​​​​​​​​​​​​​

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02 How Insulin Resistance in Your Brain Fuels Cognitive Decline (Even Without Diabetes)

Let's zoom in on a concept that's not well misunderstood: neuronal insulin resistance - the topic of item 1 above.

Many of us associate insulin resistance primarily with type 2 diabetes, where the body's cells don't respond well to insulin, leading to high blood sugar. But here’s the surprising part: your brain can develop insulin resistance independently of whether you have systemic diabetes.

Here's what to know:

• Research has identified neuronal insulin resistance occurring independently of systemic diabetes, particularly in aging populations. For example aging, inflammation, and oxidative stress all lead to neuronal insulin resistance.
• This "brain-specific" insulin resistance means that even if your blood sugar levels are normal, your neurons might still be struggling to effectively use glucose, their primary fuel.

⇒ However, you may not notice until the neurons are damaged beyond repair.

What this means for you: This is a critical distinction that shifts our focus from just blood sugar numbers to the health of our brain at a cellular level. It means you can't assume your brain is fine just because you don't have diabetes.

Mid-life is the critical time to act:

• Don't Rely Solely on Diabetes Screenings: While managing systemic metabolic health is crucial, understand that your brain might be experiencing insulin resistance even if your A1c is normal. This reinforces the need for proactive brain health strategies.
• Look Beyond Obvious Symptoms: Early signs of cognitive decline or brain fog could be subtle indicators of neuronal insulin resistance. Don't dismiss them as just "getting older."
• Embrace a Brain-Protective Lifestyle: The same principles that support systemic insulin sensitivity (which we'll discuss more in the next item) also benefit your brain directly.

⇒ Understanding brain-specific insulin resistance empowers you to be more proactive about your cognitive future, ensuring your most vital organ gets the fuel it needs to remain healthy.

Related: Why Walnuts Lower Heart Disease and Help You Sleep Better​​​​​​

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03 Your Gut's Hidden Role: How Modern Diets Drive Brain Inflammation

We've talked about the critical midlife window for brain aging and the silent threat of neuronal insulin resistance.

Now, let's connect some dots. It might seem obvious that what you eat affects your body, but new research is revealing just how intimately your daily food choices, particularly typical Western dietary patterns, directly contribute to cognitive decline.

Modern diets - characterised by high amounts of processed foods, refined carbohydrates, and unhealthy fats - are a significant source of chronic, low-grade inflammation throughout your body.

Via our Gut-Brain Axis these diets can directly impact the integrity of your blood-brain barrier (BBB), the crucial protective shield around your brain

When the BBB is compromised, it can deprive your brain of optimal fuel and hence negatively affect its delicate metabolic balance in the same way as neural insulin resistance. Hence lead to accelerated later life cognitive decline.

This is a surprising consequence because many people don't fully grasp the direct brain impact of a diet high in processed foods and refined sugars.

⇒ These foods don't just affect your waistline; they create an internal environment that is detrimental to your brain's long-term health and resilience..

What this means for you: The good news is that choosing whole, nutrient-dense foods can significantly improve your brain health now and in your later years.

Ditch the processed stuff - cut down on refined sugars, highly processed foods, and unhealthy fats; and, focus on a diet rich in whole foods - plenty of vegetables, fruits, lean proteins, healthy fats (like those from avocados, olive oil, nuts, and seeds), and complex carbohydrates.

⇒ You know what to do. Think about yourself at 70 and how much better you will be by starting now.

Related: ​​​​This One Exercise Will Reshape Your Body And Your Brain, If You’re Game​​​​​​​​​​​​

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04 HIIT Squats - Yes You Can Hit Those Mitochondria

Our exercise of the week is ... the seated row, with resistance bands.

The seated row is a specific, powerful exercise you can do with a simple resistance band that directly improves your brain's metabolic health.

You might think of the seated row as just an exercise for your back and arms. And while it will do wonders in building your upper body strength and improving posture, here's the surprising, brain-boosting secret: by engaging large muscle groups in your upper back and arms, the seated improves your body's overall insulin sensitivity and glucose metabolism.

This means that you brain benefits because when your muscles are efficient at absorbing sugar, it creates a healthier, less inflamed, and more stable metabolic environment. This means there's less "noise" or "stress" in the system, allowing your brain to function more smoothly.

What this means for you: If you want a specific, actionable way to improve your brain's metabolic health and fight against neuronal insulin resistance, this exercise is a fantastic addition to your routine.

• Sit on the floor or a sturdy chair with legs extended (slight knee bend okay). Loop the resistance band around your feet and hold an end in each hand, palms facing each other or down. Sit tall with a straight back and engaged core.
• Pull the band toward your torso by bending elbows and squeezing shoulder blades together, then slowly extend arms forward to return to start.

Do 2-3 sets of 10-15 reps, 2-3 times a week. Start light and increase resistance as you get stronger.
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See this video which explains in 22 secs. Main point: slow extensions.

Related: ​How To Go From On-knee to Full Pushups, and Reap The Benefits​​​​​​​​​​​​​​

Thanks for reading!

>> My Latest Blog Post: Energise Your Golden Years: Boosting Your Desire to Exercise with Gut-Healthy Foods​

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