Have Fungi Hacked Us?

Have Fungi Hacked Us? - The Spore Report Skip to content March 18, 2026 March 18, 2026 The science of how the fungal kingdom may be shaping your mood, your cravings, and your mind – from the inside. Here’s a thought experiment. What if the cravings you experience for sugar, for alcohol, or bread aren’t entirely yours? What if some portion of what you interpret as desire or appetite is being subtly shaped by organisms living inside you that benefit from those exact choices? It sounds like science fiction. But it’s not. Fungi have been co-evolving with animal biology for hundreds of millions of years. In that time, certain species have become extraordinarily good at surviving inside a host. And one of the more striking things that’s emerged from recent microbiome research is that the fungal organisms living in your gut (your myco biome) are not passive passengers. They are biologically active participants in a conversation that runs all the way to your brain. So what exactly are they saying? The Cordyceps Problem To understand why this question makes scientists nervous, you need to know about Cordyceps. Cordyceps is a genus of parasitic fungi that infects insects and does something genuinely extraordinary (and horrifying). After colonising its host, it manipulates the insect’s behaviour with precision. An infected ant will climb vegetation, grip a leaf vein at an elevation optimal for spore dispersal, and die in exactly that position. The fungus is essentially controlling the ant. The mechanism involves fungal compounds interacting with the host’s nervous system, altering motor control, suppressing normal behaviour, and substituting the fungus’s reproductive interests for the organism’s own survival instincts. Now, before you spiral, this does not happen in humans (The Last Of Us was science fiction). Cordyceps fungi are highly host-specific, having co-evolved with particular insect species over millions of years. There is no credible pathway by which something analogous is occurring in human neurology. But Cordyceps is not an anomaly in the fungal kingdom. It’s an extreme example of a much broader biological reality. Fungi, as a group, are extraordinarily sophisticated at chemically influencing the organisms they inhabit. The question isn’t whether they have this capacity, the question is what that would look like in a host as complex as a human being. Could a subtler version of that influence already be operating inside us? The Social Mice In 2022, immunologist Iliyan Iliev and his colleagues at Weill Cornell Medicine ran an experiment with a result that, by his own account, surprised them. They introduced Candida albicans (a common gut-dwelling fungi in humans) into the digestive systems of mice. The expected finding was immunological. And sure enough, the fungi-colonised mice showed greater resilience in their gut linings when challenged with bacterial infection. The gut wall appeared to strengthen. Normal enough. The unexpected finding was behavioural. Mice with Candida in their guts were measurably more sociable. They were more likely to sniff, communicate with, and engage with other mice. Their behaviour had been altered, apparently through the presence of a fungus in their digestive tract, not their brain. The mechanism Iliev’s team identified was indirect. Certain molecules released by immune cells, responding to the fungal presence, appeared to enter the bloodstream and stimulate nerve cells in the brain involved in behaviour. The fungus was pulling on the immune system’s strings. The immune system was pulling on the brain’s. “It was very surprising to us,” Iliev said. And the question his team couldn’t answer is whether this effect is incidental or adaptive. Is it a coincidence that fungal presence triggers immune signals that alter social behaviour? Or is the fungus, in some evolutionary sense, doing this? Is it increasing host sociability to improve its own chances of spreading between hosts through social contact? That question remains open. The fact that it’s being asked seriously, by scientists at major research institutions, tells you something about how far this field has moved in a short time. The Gut-Brain Pipeline To understand how fungi could plausibly influence human mood and behaviour, you need to understand one of the most consequential discoveries in modern biology: the gut-brain axis. Your gut and your brain are in constant, bidirectional communication. This communication is done through the vagus nerve, through immune signalling, and through the production of neurotransmitters. Roughly 90% of your body’s serotonin is produced in your gut. So the brain doesn’t generate most of its own serotonin. It receives it from below. This means that anything living in your gut that can influence the biochemical environment there, has, in a very real sense, a hand on the dial of your emotional experience. And fungi are not small players in that environment. Despite comprising only around 0.01–0.1% of the gut microbiome by numbers, their larger cell size and unique immunological properties give them an influence disproportionate to their abundance. They interact directly with the gut wall. They modulate immune responses. They produce metabolites that enter the bloodstream and reach the brain. As Matthew Olm, microbiologist at the University of Colorado Boulder, puts it: “there’s no reason to think that fungi aren’t doing this”, influencing the brain through the same immune and nervous system pathways that bacteria are now known to use. The evidence that this matters clinically is accumulating. A 2024 review in Frontiers in Cellular Neuroscience catalogued the emerging links between gut mycobiome disruption and neuropsychiatric conditions. Dysbiosis – an imbalance in the fungal community, often involving overgrowth of opportunistic species – has been associated with disruptions in serotonin and dopamine pathways, neuroinflammation, and conditions including depression, bipolar disorder, and anxiety. Reduced fungal diversity correlates with schizophrenia. Fungal metabolites appear to contribute to blood-brain barrier dysfunction. These are peer-reviewed findings from major journals, and the research is accelerating. Candida, Cognition, and Schizophrenia Perhaps the most striking human evidence comes from Johns Hopkins neuroscientist Emily Severance and her colleagues. In a 2016 study , Severance examined women with schizophrenia and found something that those who showed signs of elevated exposure to Candida albicans tended to score significantly lower on tests of memory and other cognitive abilities than schizophrenia patients without elevated Candida. Severance’s hypothesis is that Candida overgrowth provokes a disruption in the gut’s microbial balance, altering the compounds the gut produces in ways that may make susceptible people more likely to develop or worsen schizophrenia symptoms. If that’s true, it opens a novel treatment avenue: managing schizophrenia, at least in part, by addressing the fungal imbalance in the gut with probiotics. “I think that that’s typical for a field of study that is very exciting, but still very early on in the timeline,” Severance said. It’s worth being clear-eyed about what this does and doesn’t show. Finding an association between Candida levels and cognitive impairment is not the same as proving that Candida causes schizophrenia. People with schizophrenia may be more prone to Candida overgrowth for independent reasons like medication, diet, stress, and lifestyle. The causal arrow is not yet established. But the association is there, it’s been replicated in adjacent research, and the biological mechanism by which it could be real is plausible and increasingly well-mapped. The question has moved from “is this worth studying” to “how does this work.” The Craving Hypothesis Here’s where it gets uncomfortable. One of the more speculative theories emerging from mycobiome research is that certain gut fungi may be influencing cravings for the foods that sustain them. Candida, for instance, thrives on sugar and simple carbohydrates. It produces compounds that interact with the gut lining and potentially with neural pathways involved in appetite and reward. When Candida populations are elevated, the gut environment shifts, and some researchers have proposed that this shift may feed back into the host’s dietary preferences in ways that favour continued fungal proliferation. Let’s be precise about what is and isn’t established. There is no direct human study that has proven a causal link between Candida overgrowth and sugar cravings. The mechanisms are biologically plausible, and there is suggestive evidence from animal models, but human causality remains to be demonstrated rigorously. But the broader principle – that gut microorganisms can influence host appetite and food preference – is now well-supported. The mechanisms exist. The signalling pathways are real. And given the Iliev mouse study, in which gut fungi measurably altered social behaviour through immune-neural pathways, the idea that the same infrastructure could be influencing appetite feels less like speculation and more like an obvious next experiment. The pattern, across the animal kingdom, is consistent. Fungi influence pollinator behaviour by altering flower chemistry. They manipulate the foraging patterns of insects. They change the positioning of their hosts. Across the fungal kingdom, the capacity to influence host behaviour through chemistry is a recurring evolutionary solution. The idea that humans are somehow exempt from any version of this influence is the claim that actually requires justification. Fungi in the Brain This story goes beyond mood and behaviour, and into the possibility that fungi, when they reach the brain directly, may be contributing to some of the most feared diseases of ageing. Fungi rarely cross the blood-brain barrier in healthy people. But molecular biologist Richard Lathe at the University of Edinburgh has been building a case, considered controversial but taken seriously in some circles, that microbes including fungi slip across that barrier more frequently than assumed. In older people, whose immune systems have weakened, this accumulation over time may be contributing to the neuroinflammation that characterises Alzheimer’s disease. The evidence is circumstantial but not trivial. In several documented cases, patients initially diagnosed with Alzheimer’s symptoms were found, on closer examination, to have fungal or microbial brain infections. When treated with infection-fighting medication, some showed remarkable cognitive improvement. In a few cases, they even returned to work. Lathe and colleagues examined brain slices from deceased Alzheimer’s patients and found higher quantities of microbial material than in healthy controls. It’s contested. Critics point out that microbial fragments are ubiquitous and contamination is hard to rule out. Causality is unproven. But new evidence from a 2024 study – in which scientists tagged bacteria with fluorescent markers and watched them travel, over the course of a week, into the brains of salmon and trout, apparently living there without obvious harm – has made the hypothesis feel more plausible. If microbes routinely enter fish brains and persist there, the barrier to the same being true in mammals, including humans, looks considerably lower than we once assumed. “I think we’ve now reached that threshold where there’s enough smoke around this hypothesis,” Olm says, “it’s worth spending money on figuring out if that is happening.” What Disruption Looks Like If fungal communities inside us are participating in the regulation of mood, cognition, and behaviour under healthy conditions, then what happens when those communities are disrupted becomes urgent. And they are being disrupted at a scale and in ways that have no precedent in human evolutionary history. The factors that most reliably degrade mycobiome diversity are antibiotics, which reshape the entire gut microbial landscape including fungi; a diet high in processed food and low in fibre; chronic stress; and age. These are not niche concerns. They describe the baseline conditions of modern industrial life. When opportunistic species like Candida overgrow in the absence of a balanced microbial community, the consequences appear to extend well beyond digestion. Neuroinflammation. Increased gut permeability that allows fungal metabolites and immune-activating compounds into the bloodstream. Disrupted neurotransmitter production. Altered immune responses that affect the brain. And, if Severance’s hypothesis is correct, a measurable impact on cognitive function and psychiatric vulnerability. The troubling possibility is that the epidemic of mood disorders, anxiety, cognitive fatigue, and motivational dysfunction that characterises modern populations isn’t only, or even primarily, a psychological phenomenon. It may be, at least in part, a mycobiome phenomenon. An ecological disruption inside us that we’ve been treating with drugs that target the brain, while the actual disturbance is happening one level below in the gut, in the fungal and bacterial communities that regulate the neurochemical environment the brain depends on. Not Control. Something More Interesting. It’s important not to lose the thread of what the science is and isn’t showing. Fungi are not controlling you. They do not have grand intentions. They are not running a coherent programme aimed at directing your behaviour. The Cordyceps framing, as compelling as it is as metaphor, misrepresents the biology in ways that matter. What’s happening is more distributed, more ecological, and in some ways more profound than control. The fungi inside you are part of the system that produces you, including the version of you that experiences moods, has cravings, makes decisions about what to eat, how to feel, how to engage with the world. They are not external agents exerting influence on a separate “you.” They are participants in the biological processes that constitute your experience. When that community is healthy and diverse, the system is in something like ecological balance, and the neurological and emotional outputs of that system reflect it. When it’s disrupted, the outputs shift. Because you and the fungi are essentially the same system. That is not a conspiracy. And the reason it matters is that it suggests a fundamentally different frame for thinking about mental health, cognitive performance, and chronic disease. It moves the focus from the brain or even individual behaviour, to in the invisible ecosystem that has been co-regulating human biology since long before we existed as a species. The fungi haven’t hacked you. They are a part of you. And we’re currently finding out what happens when we neglect them. The Spore Report explores the science of fungi, regenerative biology, and what living systems can teach us about health. Sign up here. Related Posts The Brain’s Hidden Architecture Looks Suspiciously Like a Fungal Network, According to New Research For decades, neuroscientists have been hunting for the seat of intelligence in the brain. 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