14 Days on Freeze-Dried Food Reshapes Gut Bacteria in Surprising Ways

Five volunteers checked into the LunAres Research Station in Piła, Poland, a simulated space habitat, and ate nothing but industrially prepared, freeze-dried meals for 14 days. The question the researchers wanted to answer was straightforward: what does an exclusively freeze-dried diet do to the trillions of bacteria living in the human gut? A preliminary study published in Current Research in Food Science suggests the answer is complicated, and deeply personal.

Freeze-dried diet produces highly individual gut microbiome shifts

At the cohort level, overall gut microbiota diversity showed no statistically significant change after the two-week intervention. But that headline number conceals a striking degree of individual variation. Bray-Curtis dissimilarity scores, a measure of how much a microbial community changes between two time points, ranged from 0.24 to 0.86 across the five participants. In plain terms, some participants' gut communities barely budged, while others were substantially remodeled.

The most dramatic individual shift involved Prevotella copri, a species associated with plant-rich diets. In one participant, its relative abundance jumped from 0.25% or less at baseline to 44.2% by day 14. No other participant showed anything close to this. Meanwhile, several species associated with gut health declined across multiple participants: Eubacterium rectale, Blautia obeum wexerae, and Roseburia species all decreased, as did Bifidobacterium adolescentis, a microbe involved in oligosaccharide digestion and lactic acid production. On the positive side, Faecalibacterium prausnitzii, known for its anti-inflammatory properties and its role in producing the short-chain fatty acid butyrate, increased. One species held steady throughout: Ruminococcus bromii, a key player in complex carbohydrate metabolism, remained stable across participants and was identified as part of the core microbiome.

These findings matter because diet is one of the most powerful levers acting on gut microbiome diversity, shaping which bacterial species thrive and which decline over remarkably short timescales.

What this means for astronauts, expedition teams, and remote workers

Freeze-drying reduces the free water content of food to between 1% and 4%, preventing microbial growth and dramatically extending shelf life. That makes it the default provisioning choice for space missions, polar expeditions, and military deployments where fresh food is impossible to supply. Roughly 425 bacterial species were identified across the ten fecal metagenomes in this study, with the top 30 taxa accounting for 75% to 86.2% of each community. The fact that even a short exposure to a controlled freeze-dried diet can drive substantial compositional shifts in some individuals raises a practical concern: if certain gut bacteria linked to immunity and inflammation decline during missions, performance and health could follow.

The stakes are not trivial. Dysbiosis, or an abnormal shift in gut bacterial composition, has been linked to inflammatory bowel disease, obesity, and certain cancers. Whether a 14-day freeze-dried diet is enough to push anyone toward clinically meaningful dysbiosis remains an open question, but the idiosyncratic nature of the responses suggests that one-size-fits-all dietary planning for long-duration missions may be insufficient.

How the team profiled bacterial communities at species level

Rather than the more common 16S rRNA gene amplicon approach, the researchers used shallow shotgun metagenomics, sequencing DNA extracted directly from fecal samples with the QIAmp PowerFecal Pro DNA kit. Libraries were prepared with the KAPA Hyper Plus kit and run on an Illumina MiSeq System using 2×150-cycle paired-end sequencing; only forward reads were used in downstream analysis. Taxonomic profiles were generated with the NGless pipeline (version 1.3.0) and the mOTUs module (version 2.6), enabling species-level identification. Alpha diversity was assessed using Observed species counts, Chao1, Shannon, and Simpson indices. Beta diversity relied on Bray-Curtis dissimilarity. Statistical comparisons used paired Wilcoxon signed-rank tests with Benjamini-Hochberg correction for multiple comparisons.

Participants ate five controlled meals per day totaling 2,880.5 kcal on average, with macronutrient ratios set at 15 to 20% protein, 35 to 40% fat, and 45 to 50% carbohydrates. Snacking was not allowed, and compliance was monitored throughout. Fecal samples were collected at baseline and at the 14-day endpoint.

Small sample size and confounding habitat effects limit the conclusions

With only five participants, the study lacks statistical power to draw generalizable conclusions. The authors are explicit about this; the word "preliminary" appears in the title itself. Shallow shotgun sequencing, while more species-specific than 16S amplicon methods, still has limited resolution for low-abundance taxa and cannot easily capture functional pathway data. Species-level taxonomic classification from metagenomic data carries its own reliability challenges, including biases introduced by sequencing platforms and data-processing software choices.

Beyond the sequencing caveats, the LunAres habitat itself introduces variables that are impossible to fully untangle from diet. Participants were confined to an analog station, with altered sleep schedules, social dynamics, physical activity patterns, and psychological stress all potentially influencing microbiome composition independently of what they ate. No detailed dietary records or biomarkers of adherence were collected, and participants had only a basic health assessment before entry, meaning undiagnosed conditions were not ruled out. The intervention also lasted just 14 days, which may not be long enough to observe the full arc of microbiome adaptation.

Longer missions and larger cohorts are the logical next step

The researchers frame this work as groundwork for studying what happens to the gut during genuine space missions and extended wilderness expeditions. Translating microbiome research into real-world nutritional interventions remains a major challenge, but studies like this one help map the territory. The highly individual nature of the responses points toward a need for personalized gut microbiome baselines before any extended freeze-dried diet deployment, so that worrying shifts can be detected early.

Freeze-drying does preserve probiotic viability at rates of 75% to 98.6%, which suggests that purpose-formulated freeze-dried meals containing beneficial live bacteria could theoretically support gut health during missions. Whether that potential can be realized in practice, and whether the changes seen here persist, reverse, or intensify over 30, 60, or 180-day timescales, are questions this small pilot study cannot answer. A larger, longer, and more tightly controlled trial is the obvious next move.

Evidence rating

INVESTIGATIONAL — 63/100

Caveats:

• Only five participants were enrolled — far too few to detect reliable effects or generalize findings.
• No statistically significant changes were found; individual-level shifts cannot be distinguished from normal day-to-day microbiome variation at this sample size.
• The study was conducted in a space-analog habitat where confinement, stress, and altered physical activity could independently affect the microbiome.
• Funding was not disclosed by the authors.
• This is an explicitly preliminary study; the authors themselves call for larger controlled trials before drawing conclusions.

Preliminary controlled dietary intervention (n=5) conducted over 14 days in a space-analog habitat. No statistically significant changes in alpha or beta diversity were detected; individual-level taxonomic shifts were observed but cannot be distinguished from biological variation at this sample size. The study has not been independently replicated and is explicitly described by the authors as hypothesis-generating.

References

1. Błażejewska-Stuhr Katarzyna, Cembrowska-Lech Danuta, Krauze Wiktoria, et al. (2026). The impact of freeze-dried food on gut microbiota composition: a preliminary study. Current Research in Food Science. https://doi.org/10.1016/j.crfs.2026.101470
2. Ping Zhang (2022). Influence of Foods and Nutrition on the Gut Microbiome and Implications for Intestinal Health. International Journal of Molecular Sciences. https://doi.org/10.3390/ijms23179588
3. Yu-Jie Zhang, Sha Li, Ren-You Gan, Tong Zhou, Dong-Ping Xu, Hua-Bin Li (2015). Impacts of Gut Bacteria on Human Health and Diseases. International Journal of Molecular Sciences. https://doi.org/10.3390/ijms16047493
4. Simone Filardo, Marisa Di Pietro, Rosa Sessa (2024). Current progresses and challenges for microbiome research in human health: a perspective. Frontiers in Cellular and Infection Microbiology. https://doi.org/10.3389/fcimb.2024.1377012
5. Tiffany L. Weir (2023). Grand challenges: Actualizing the potential of the gut microbiome to address global nutrition challenges. Frontiers in Microbiomes. https://doi.org/10.3389/frmbi.2023.1146827