The Energy Shift:
How declining ovarian oestrogen triggers a fuel change in the brain

You may recognise yourself here if your energy shift is struggling

One of the most confusing things about menopause is how many of these can seem to arrive at once. Sleep starts breaking. The mind feels foggy. Anxiety appears from nowhere. The body feels more reactive. Tired but wired. Weight shifts, especially around the middle. Hot flushes and palpitations begin. Mood feels flatter, or more fragile, or just not like you.

It can feel chaotic. These symptoms are not random. They are different expressions of one underlying shift in how the brain and body are trying to manage energy.

The brain is trying to change fuel

The brain is an engine that can run on two fuels.

Glucose — sugar and starch from carbohydrates such as pasta, bread, oats, lentils, cakes, chocolate, fizzy drinks.

Ketones — made in the liver when the body can burn its own fat.

When running the menstrual/fertility code, oestrogen keeps the glucose system running smoothly. It stimulates the production of glucose transporters which ferry glucose into the cells, with the help of insulin. At the same time, it holds the ketone system on the back burner. While oestrogen is present, glucose is an easily accessible fuel and the brain is well supplied even on a high-carbohydrate diet.

At menopause, when oestrogen declines, two things happen at once.

First, the glucose supply to the brain is significantly blocked. Fewer transporters are made and less glucose gets through to brain cells, regardless of how much glucose is in the blood. Unused glucose pools in the blood – which can cause insulin resistance – and is stored as fat.

Second, the decline in oestrogen is also the signal that triggers the ketone system back on, and maximises it for fat burning. Scientists at the University of Southern California have shown that before menopause oestrogen keeps the ketone system in the background while glucose is dominant. At menopause, as oestrogen falls, that glucose-dominant architecture is released and the ketone system is reinstated as the brain’s alternative energy pathway (Brinton et al., 2015).

Ketones are the perfect energy fuel now – they do not need insulin or transporters to reach brain cells. They get there directly. They burn more cleanly than glucose and produce steadier, more reliable energy. A brain that completes the transition from glucose to ketones is not just well fuelled — it is calmer, sharper and more resilient than it was before menopause. This is part of the menopausal code.

The trouble is, a modern diet keeps the shift from happening

There is one condition. The liver can only make ketones when insulin is low. A modern diet — high in bread, pasta, rice, sugar, processed food — keeps insulin high almost continuously. When insulin is high, the liver cannot make ketones. The brain is losing its glucose supply and never receiving its ketone supply. It is stranded between two fuel systems, unable to fully access either.

This is an energy deficit.

The energy deficit in a three step loop

Step 1. Sugar and carbohydrate come in. 
Bread, pasta, rice, oats, cereals, biscuits, cakes, potatoes, beans, lentils, chickpeas, processed food, added sugar — the foods that form the backbone of a modern diet — all break down into glucose. In the reproductive years, oestrogen helped the body handle that load by keeping insulin sensitivity high and supporting the brain’s glucose transporters. After menopause, without that support, the same carbohydrate intake hits differently.

Step 2. Sugar cannot be used, so it is stored as fat. 
Blood sugar spikes. Insulin surges to bring it down. Because oestrogen is no longer assisting glucose entry into cells, more of that sugar in the blood is shunted into fat storage — particularly around the middle. High blood sugar, high insulin, low fat burning. Sugar cravings. Constant snacking. Weight gain. Meno belly. Fatigue after meals, leading to more snacking on sugar. Willpower fails in the face of biochemistry.

Step 3. Fat cannot be burned, so the brain is starving. 
High insulin then locks the second door. When insulin is elevated, the liver cannot produce ketones. The brain’s backup fuel — the one it was designed to transition to — is blocked at source. The brain cannot get glucose in efficiently because the oestrogen-dependent transport system has been decommissioned, and it cannot access ketones because insulin will not let the liver make them. The brain is starving for energy in a body that is simultaneously storing fat it cannot burn.

One energy deficit, eight symptoms – the Hateful Eight

An underpowered brain reaches for the only emergency system it has — the fight-or-flight response. The hypothalamus sounds the alarm. Within seconds, adrenaline floods the bloodstream, breaks down stored glycogen in the liver and pushes the sugar straight to the brain. Then, cortisol follows to sustain the supply, prompting the liver to manufacture fresh glucose if the alarm continues.

Pre-menopause, that burst of glucose would solve the problem and the system would stand down. But now, with the Energy Shift in place, glucose struggles to enter the brain and ketones are blocked. The brain pulls the emergency lever again and again. The system that was supposed to rescue the brain becomes the thing that deepens the crisis. One energy crisis, put through a fuel-mobilising stress response, expressed in eight symptoms — what I call the Hateful Eight.

Hot flushes
The hypothalamus, which controls core temperature, is one of the first structures to feel the crisis. When it runs low on fuel, it triggers the fight-or-flight surge: sweat glands fire, skin vessels dilate, heat rushes to the surface.

Night sweats
The same surges fragment sleep. Broken sleep worsens insulin resistance and makes the next day worse. Many women wake at 3am — just at the time when cortisol is naturally rising. A high baseline cortisol amplifies the brain’s sensitivity to low fuel at that hour.

Anxiety and panic
A hypervigilant brain without a brake. Adrenaline and cortisol crank up the amygdala, the brain’s threat detector. The brain is genuinely detecting danger — its own energy deficit — and the mind wraps that signal in stories – something is terribly wrong with me! Something is wrong. It is a fuel deficiency in the brain, not an oestrogen deficiency in the body.

Heart palpitations
The heart follows orders from the panicking brain. Adrenaline speeds the rate and increases the force. The brain notices its own racing heart, interprets it as more danger, releases more adrenaline. A feedback loop of fear and physiology.

Brain fog
The brain is running on fumes. Words go missing. Focus dissolves. Chronic fight-or-flight cortisol makes it worse by suppressing the molecules the brain needs to maintain its functionality.

Low mood and depression
The neurotransmitter reward system running dry. Dopamine, the chemistry of motivation and pleasure, is produced by circuits that run on energy the brain no longer has. Anti-depressants often underperform here because they work better with oestrogen, and they were never designed to fix an energy problem.

Fatigue
Energy is on the floor, in the brain and the body. Without a steady supply of ketones and with glucose unusable, deep unrelenting tiredness sets in. In desperation the brain commandeers all available glucose, stripping it from muscles and gut. Cortisol breaks down muscle protein. Lean mass drops. And the sleep that should restore everything is itself broken by night sweats.

Weight gain
The body is hoarding the sugar energy the brain keeps demanding, as fat. Cortisol directs fat to the abdomen. Insulin prevents it from being released. The visceral fat itself worsens insulin resistance, which suppresses ketones further, which deepens the crisis — which stores more fat. Meno belly is real.

Seen one by one, these symptoms can look random, but seen together, they begin to tell a much more coherent story. You do not need to have all of them, and they do not all have to appear at once, but they point to a brain and body struggling to complete this energy shift cleanly.

Modern life can make this harder when peri/menopause begins

This shift does not happen in a vacuum – many women now arrive in perimenopause or menopause after years of:

• unstable blood sugar
• chronic stress
• broken sleep
• constant stimulation
• under-eating protein
• over-reliance on quick carbohydrates
• poor recovery
• inflammation
• depleted metabolic resilience

So by the time the brain begins this shift, it may already be working with a much more fragile energy environment than it was designed for. That is what makes the shift so symptomatic. The biology is doing what it was built to do but it is meeting a brain and a body that have been pushed to the edge of their reserves for years.

When the energy deficit resolves, the brain upgrades

The energy deficit has one weak point: insulin.

When carbohydrate load drops, insulin falls. When insulin falls, the liver makes ketones. When ketones reach the brain, the emergency alarm switches off — cortisol normalises, the thermostat steadies, fog lifts, sleep deepens, mood stabilises and weight begins to shift.

Women describe the change in plain terms:

• Sleep deepens.
• Mental clarity improves.
• Mood feels steadier.
• Flushes become less intense.
• The body feels less reactive.
• Energy becomes more reliable.

The brain is finally getting consistent access to the fuel it has been trying to shift towards.

Brain imaging shows that as the menopausal brain settles into ketone-based stability, it begins to reorganise — not decline. Iron and omega-3 availability improve. Iodine becomes more accessible for energy metabolism. The biochemical environment begins to resemble early childhood brain development, when the brain first built its high-speed wiring.

Further, newer research suggests that genes on the silent X chromosome start to wake up later in life, including genes that maintain myelin and support memory networks. It looks like rather than running out of steam, the menopausal brain is becoming more resilient, not less! As long as it is not blocked by a modern food environment it was never designed for.

HRT preserves the old brain.
Menopause builds the new one.

HRT extends the time span that women can have access to oestrogen. The functional medicine approach supports the brain to complete the fuel shift it is already trying to make.

The relevant consideration here is specific. HRT does not simply replace what is missing in the Energy Shift. It preserves the brain in a reproductive, glucose-dominant metabolic state — interrupting the upgrade the brain is designed to make.

The deeper question is not whether HRT relieves symptoms. For many women, it does. The question is whether the relief comes at the cost of holding the brain in its previous operating system, while the post-reproductive one is left unbuilt.

This is not an argument against HRT. It is an argument that the choice between options is rarely framed in these terms.

From energy deficit to a sharper, happier brain: what happens in clinic

The work begins by resolving the deficit.

My clints follow a four-week meal plan that is low in carbohydrate, high in protein and moderate in fat, adjusted to their individual needs. It is not a diet in the way most women understand the word. It is an anti-inflammatory brain-supporting nutritional tool, designed to break the cycle of sugar, insulin and inflammation that is blocking the brain’s transition, and to power up a starving brain.

Within that window, women see the Hateful Eight symptoms reverse. The fog lifts. The flushes cool. Sleep deepens. Anxiety loosens its grip. Energy returns — not the jittery, sugar-fuelled kind, but steadier, more reliable. Women describe it in different ways but the theme is always the same: I feel like myself again.

Once the brain is stable and the symptoms have reversed, the work moves into a second phase — personalising carbohydrates. Most women fear the idea of never eating carbohydrates again, and are always relieved that this is not necessary to optimise brain function in menopause. After working with hundreds of women, it became clear to me that different women can tolerate different amounts of sugar and starch before the symptoms return. I call this the carbohydrate tolerance point — the amount of carbohydrate her body can handle without tipping back into the deficit.

The carbohydrate tolerance point is not fixed. It shifts with muscle mass — muscle acts as a glucose sink, so more muscle widens the tolerance. It shifts with sleep — one bad night raises cortisol and drops insulin sensitivity. It shifts with alcohol, which disrupts blood sugar, inflames the liver and pushes the system back towards cortisol. It shifts with stress, because chronic psychological pressure keeps the stress pathways on high alert and drags the metabolism back towards emergency mode.

This is not about perfection or deprivation. It is about understanding that the brain has changed how it needs to be fed, and that once a woman learns her own carbohydrate threshold, she holds the single most powerful lever for keeping the deficit resolved and the new brain online.

Following a personalised nutrition approach adapted to their menopause means women in my clinic report an 80-100% reduction in brain fog within 2 weeks and a 75% reduction in all the hateful eight symptoms within 4 – 6 weeks.

How this compares to the latest non-hormonal drug

For comparison, the latest non-hormonal prescription drug — Veozah (fezolinetant), approved by NICE in March 2026 for moderate-to-severe hot flushes and night sweats — reduces hot flushes by approximately 7.6 events per day at twelve weeks. The placebo group reduced theirs by 5. The active-drug effect, then, is about 2.5 events per day.

The drug passed the FDA on statistical significance, not clinical significance. The difference matters. Statistical significance means the trial showed a real effect — small effects can be statistically significant if the sample is large enough. Clinical significance means the effect is big enough for a woman to notice it in her life. For hot flushes, the published threshold for an effect a woman would notice is a reduction of 3.57 events per day above placebo. Veozah’s effect is 2.5. Real, but below what the literature itself defines as meaningful (SKYLIGHT 1 and 2, ICER review, 2023).

Veozah is not recommended for women with current breast cancer, other oestrogen-dependent cancers or liver disease; women with a previous history require individual risk assessment because trial data in this group is unavailable (British Menopause Society, March 2026). Common side effects include abdominal pain, diarrhoea, insomnia and back pain, and the FDA has added a warning about rare serious liver injury (FDA Drug Safety Communication, September 2024).

For women who cannot or do not want to take HRT, Veozah is an option doctors can now offer on the NHS — however the trial data simply does not match the framing.

Is a blocked Energy Shift driving your symptoms?

A discovery call with me is a free 30-minute phone call. We talk through your symptoms, your history and what you’ve already tried. By the end, you will know whether the Energy Shift is the primary pattern and a handful of concrete levers to begin with.

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