Too Little Salt Harms Your Brain Too, New Gut-Brain Study Finds

Salt has long worn a simple villain's costume in dietary guidelines, with high intake blamed for hypertension, stroke, and increasingly, cognitive decline. But a new mouse study published in Food Research complicates that picture considerably: both long-term high-salt and long-term low-salt diets independently impaired memory and disrupted the gut-brain axis, each through its own distinct biological route. The findings are early and come with important caveats, but they raise a question that mainstream nutrition advice rarely asks: can excessive salt restriction be its own cognitive risk?

High-salt diets drive brain harm through inflammation and tau protein changes

The high-salt diet (HSD) arm of the study produced a cascade of changes that align with what researchers have been piecing together over the past several years. In the humanized control (HC) mice fed long-term HSD, the gut microbiome shifted toward pro-inflammatory microbial taxa. That shift drove up circulating inflammatory cytokines and expanded populations of TH17 immune cells, which secrete interleukin-17 (IL-17), a signaling molecule that can damage blood vessel walls. IL-17 suppresses the production of nitric oxide, the molecule blood vessels rely on to dilate and maintain adequate flow. Reduced nitric oxide, in turn, has been linked to chemical modifications in tau protein that resemble hallmarks of Alzheimer's disease pathology. The new study found HSD also caused broad lipid metabolic alterations and significantly reduced levels of the short-chain fatty acids propionate and butyrate in the gut, both of which are important signals along the gut-brain axis communication pathway. Working memory and recognition memory both deteriorated, and hippocampal synaptic proteins, the molecular machinery of learning, were measurably reduced.

Low-salt diets impair memory without triggering systemic inflammation

The more surprising half of the study involves the low-salt diet (LSD) group. These mice showed comparable memory deficits and similar reductions in hippocampal synaptic proteins, yet without the detectable systemic inflammation that characterized the HSD group. The researchers found no meaningful increase in inflammatory cytokines in the LSD animals. Instead, the cognitive impairment appeared to stem from a different failure: reduced microbial metabolic output. The low-salt mice showed decreases in propionate and butyrate, as in the HSD group, but also further drops in acetate and isobutyrate, suggesting a broader collapse of beneficial short-chain fatty acid production. The gut microbiota composition shifted as well, though in a pattern distinct from HSD. These microbiota-derived metabolites normally serve as key messengers to the brain, and their depletion under LSD conditions appears sufficient to impair cognition even when the immune system is not overtly activated. The implication is that excessive salt restriction is not biologically neutral: it creates its own form of nutritional deprivation at the microbial level.

How the researchers built the comparison

The team, led by A. Chen, S. Hu, F. Zeng, and colleagues, used humanized control mice fed either a high-salt diet, a low-salt diet, or a normal diet over a long-term period. They measured working and recognition memory behaviorally, then analyzed hippocampal synaptic protein levels, gut microbiota composition, specific metabolite concentrations including propionate, butyrate, acetate, and isobutyrate, and circulating inflammatory cytokines. The parallel design allowed the researchers to run a direct comparison between the two dietary extremes rather than benchmarking only HSD against normal intake, which is how most prior work has been framed. A cross-sectional study in older adults had previously suggested that very low sodium intake was associated with worse cognitive function, so the mouse model here provides a controlled mechanistic complement to that observational signal.

Caveats: mouse models and unmeasured human variables

The critical limitation is that this entire study was conducted in mice. Rodent gut microbiomes differ meaningfully from human ones, and the specific salt concentrations used to define low, normal, and high intake in a mouse model do not map straightforwardly onto human dietary ranges. The study cannot say how long a human would need to follow a severely salt-restricted diet before microbial metabolite deficiencies emerged, or whether the cognitive effects would manifest in the same way across different ages, sexes, or underlying health conditions. The broader literature on sodium intake and dementia risk in humans already documents that high sodium is a concern via hypertension, but the specific gut-metabolite pathway described here has not yet been validated in human populations. One additional finding from the HSD arm deserves a note: prior research showed that cognitive impairments from high-salt feeding in mice were reversible when animals returned to a normal diet, suggesting the damage is not permanent at early stages, though the new study does not directly test reversibility for the LSD arm.

What researchers need to do next

The immediate scientific priority is replication and extension: do these microbiome and metabolite changes appear in humans on clinically defined low-sodium diets, and at what threshold? The study opens a door toward microbiome-targeted interventions as a potential strategy, such as short-chain fatty acid supplementation or targeted probiotic use to restore the microbial metabolic output that low-salt diets appear to suppress. For now, the takeaway from the full study in Food Research is narrower but worth noting: in this mouse model, the gut-brain axis is sensitive to extremes in both directions, and the mechanisms driving harm differ enough that a single dietary intervention is unlikely to address both. Balanced salt intake, the study concludes, matters for cognitive health, and the biology behind excessive restriction deserves far more attention than it has received.

Evidence rating

INVESTIGATIONAL — 75/100

Caveats:

• This study was conducted entirely in mice; results may not translate directly to humans.
• Funding was not disclosed by the authors.
• Causal mechanisms are proposed but not fully validated; this is a single study without independent replication in humans.

Mouse study using a humanized microbiota model; no human participants enrolled. Demonstrates associations between dietary salt extremes, gut microbiota shifts, short-chain fatty acid depletion, and cognitive impairment, but cannot establish causation in humans. Findings are consistent with prior high-salt literature but the low-salt cognitive risk pathway has not yet been independently replicated.

References

1. Anji Chen, Shilong Hu, Fansen Zeng, et al. (2026). Long-term low-salt and high-salt diets differentially disrupt the gut–metabolite–brain axis and induce cognitive impairment. Food Research International. https://doi.org/10.1016/j.foodres.2026.119719
2. High-salt diet triggers changes in mouse brains | National Institutes of Health (NIH). NIH. https://www.ninds.nih.gov/news-events/news-releases/high-salt-diet-triggers-changes-mouse-brains
3. The gut-brain connection: What the science says – Stanford Medicine. med.stanford.edu. https://med.stanford.edu/news/all-news/2025/03/gut-brain-connection.html
4. Hany Ahmed, Quentin Leyrolle, Ville Koistinen, et al. (2022). Microbiota-derived metabolites as drivers of gut–brain communication. Gut Microbes. https://doi.org/10.1080/19490976.2022.2102878
5. Association between Dietary Sodium Intake and Cognitive Function in Older Adults – PMC. NIH. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3594191/
6. Devi Mohan, Kwong Hsia Yap, Daniel Reidpath, et al. (2020). Link Between Dietary Sodium Intake, Cognitive Function, and Dementia Risk in Middle-Aged and Older Adults: A Systematic Review. Journal of Alzheimer's Disease. https://doi.org/10.3233/jad-191339
7. Pegah Ataei, Hamidreza Kalantari, Tamara S. Bodnar, Raymond J. Turner (2026). The gut–brain connection: microbes’ influence on mental health and psychological disorders. Frontiers in Microbiomes. https://doi.org/10.3389/frmbi.2025.1701608