Inflammation, Depression, and the Gut-Brain Axis

Alex Applebee and A. D. Masters

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A Unified Thesis on the Environmental Origins of Mental Illness

Authors: Alex Applebee and A. D. Masters

Date: March 2026

Series: OMXUS Research Papers

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Author's Note

This paper exists because we watched the wrong people get blamed.

A woman sits in a GP's office. She hasn't slept properly in months. Her joints ache. She can't think clearly. She has a feeling she describes as heaviness — not sadness exactly, more like her body is made of concrete. She's been eating what she can afford, which is mostly packaged food from the middle aisles of the supermarket, because the rent took everything else. She works 40 hours a week at a job that treats her like furniture. She hasn't seen her friends in weeks because there's no time, no money, and no energy. Her gut has been wrong for as long as she can remember.

The GP writes a prescription for an SSRI. The explanation: your brain doesn't make enough serotonin. The implication: the problem is in your head.

That explanation is wrong. Not partially wrong. Not oversimplified. Wrong. The most comprehensive review of the serotonin hypothesis ever conducted — Moncrieff et al., 2022, published in Molecular Psychiatry — found no consistent evidence that people with depression have lower serotonin activity than people without depression. Thirty years of public health messaging, pharmaceutical advertising, and clinical practice built on a foundation that the evidence does not support.

But here is what the evidence does support: what that woman is experiencing is an inflammatory response. Her body is inflamed. The ultra-processed food is inflamed. Her gut microbiome is disrupted. The disrupted gut is sending inflammatory signals through the vagus nerve directly to her brain. The chronic s