When the Mind and the Metabolism Are Not Separate Problems

A patient tells me their mood has been low for months. Another tells me their concentration has simply gone, that they can no longer think as clearly as they used to. A third mentions, almost as an aside, that their blood sugar has been creeping up for years. Increasingly, when I look closely enough, these are not three separate problems. They are one problem, seen from three different angles.

Over the past few years, working across hormones, gut health and longevity medicine, I have started noticing this pattern more often than I once did: patients with mood, memory or concentration problems who also show signs of metabolic dysfunction, insulin resistance, weight gain around the middle, blood sugar that runs high without yet reaching a diabetes diagnosis. Conventional medicine tends to treat these as unrelated. One goes to a psychiatrist. The other goes to a GP for cholesterol and blood sugar. The research increasingly suggests they may be looking at the same underlying process through two different doors.

Why would blood sugar affect the brain?

The brain runs almost entirely on glucose for fuel. When the body becomes resistant to insulin, the hormone that lets cells take up glucose, that resistance often shows up in brain tissue too, even in people whose blood sugar still looks normal on a standard test. The result is a state researchers call cerebral glucose hypometabolism: brain cells struggling to take up the fuel they need, even though there is plenty of glucose in the blood. It is a bit like a delivery van full of parcels sitting outside a warehouse whose doors will not open. The fuel is there. The brain cannot get to it.

This mechanism is now being studied across a genuinely broad range of conditions, from mood disorders to neurodegenerative disease. It does not mean metabolic dysfunction causes any of these conditions on its own. It means that when the brain’s main fuel supply is disrupted, the effects can show up as changes in mood, cognition and mental state, not just as changes on a diabetes screening test.

What does the research actually show?

Three findings, from three separate research groups, point in the same direction. Adults with pre-diabetes are 2.7 times more likely to go on to develop major depression. People newly diagnosed with bipolar disorder are 3.5 times more likely to also have metabolic syndrome. People newly diagnosed with schizophrenia are 3.7 times more likely to also have insulin resistance.

None of this means metabolic problems cause these conditions, or that treating metabolic health cures them. What it means is that the two travel together far more often than a standard assessment, which typically looks at only one side, would ever pick up. If you live with bipolar disorder or schizophrenia, or love someone who does, this research does not change the importance of ongoing psychiatric care. It is a reason to look at metabolic health alongside that care, never instead of it.

Is there early evidence this can actually be acted on?

A small pilot study published in 2025 followed 20 adults with stable bipolar disorder over eight weeks on a ketogenic diet. Participants were in ketosis 91% of the time. Higher ketone levels correlated with improved mood and energy, and with lower anxiety and impulsivity. Brain glutamate, a marker linked to mood instability, fell by 9 to 13%, among the largest reductions recorded in a study of this kind. Seven of the twenty participants asked to stay on the diet after the study ended.

This was a small, short pilot study. It is not proof that diet can replace psychiatric treatment, and any dietary change of this kind for someone with a diagnosed mood disorder should be made alongside a psychiatric team, never as a substitute for one. What it does show is that metabolic state and brain chemistry are more closely linked than most treatment plans currently assume, and that this link is measurable, not theoretical.

Psychiatry is starting to treat brain inflammation as a medical priority

Metabolic dysfunction is not the only trigger for brain inflammation. A 2025 review from King’s College London, the University of Oxford and the University of Liverpool looked specifically at psychiatric outcomes after encephalitis, brain inflammation caused by infection or an autoimmune reaction. Dr Thomas Pollak, Reader in Immunopsychiatry at King’s College London, put the finding plainly: “Psychiatric complications are common and can be disabling. For many of these, we have highly effective treatments. Mental health assessment needs to be a routine part of post-encephalitis care and never be an afterthought. Patients do not need to suffer in silence.”

Metabolic dysfunction is not the only route into this kind of inflammation either. The gut is one of the most important, and most overlooked, points of contact the body has with its own immune system. The majority of the body’s immune tissue sits along the gut lining, which means the state of the gut has a direct say in how active, or how inflamed, the immune system runs more broadly. When the gut barrier becomes more permeable than it should be, or when the balance of gut bacteria shifts, the immune system can settle into a low-grade, ongoing state of activation that does not stay confined to the gut. That same inflammatory signalling can reach the brain, feeding into exactly the kind of neuroinflammation this piece has been describing.

Metabolic health and gut health are also closely intertwined, each one quietly able to worsen the other. Insulin resistance can weaken the gut barrier, and a weakened gut barrier can, in turn, drive the kind of low-grade inflammation that makes insulin resistance worse. Neither exists in isolation, which is exactly why looking at only one side of this picture so often fails to explain what a patient is actually experiencing.

The trigger in that King’s College London review was different to the one this piece is about, but the direction of travel in psychiatry is the same wherever the inflammation comes from: stop treating mental health assessment as an afterthought. Metabolic dysfunction matters here precisely because, unlike many triggers of brain inflammation, it is common, it is measurable on a standard blood panel, and it is often modifiable. That combination is what makes it worth assessing for as a matter of routine, not just in patients who already carry a psychiatric diagnosis.

What does brain-healthy eating actually mean?

Three principles come up again and again in this research, and they are simpler than most nutrition advice.

• Nourish: build meals around real, whole animal foods, and go easy on grains and legumes, which are harder for many people to process well.
• Protect: limit refined carbohydrates, ultra-processed foods, alcohol and the vegetable oils that dominate most packaged food, all of which place an ongoing burden on metabolic function.
• Energize: keep glucose and insulin in a healthy range, and calibrate carbohydrate intake to your own metabolic tolerance rather than a one-size-fits-all rule. What works for one patient’s metabolism will not work for another’s, which is exactly why this needs to be personal, not generic.

Further reading

For patients who want to go deeper into this connection, I often recommend Metabolic Madness by Dr Rachel Brown, which sets out in accessible terms why metabolic health may be one of the more overlooked levers in mental health.

What this means at The Schoeman Clinic

This is exactly why metabolic and inflammatory markers are part of how every patient is assessed here, not only those who come to us with a mood or cognitive complaint. If you have been told your bloods are normal but you do not feel like yourself, it may be worth asking what a fuller picture would show.

If this resonates, get in touch to find out whether a metabolic and inflammatory assessment could help explain what you have been feeling.

References

• Watson KT, et al. American Journal of Psychiatry, 2021.
• Coello K, et al. International Journal of Bipolar Disorders, 2019.
• Tomasik J, et al. JAMA Psychiatry, 2019.
• Campbell IH, et al. BJPsych Open, 2025.
• Watson C, Pollak TA, Fanshawe JB, et al. King’s College London, University of Oxford and University of Liverpool review of psychiatric outcomes after encephalitis, 2025.
• Brown R. Metabolic Madness: Understand Why Metabolic Health Is Key to Mental Health.