The impact of freeze-dried food on gut microbiota composition: a preliminary study

Freeze-dried food is widely used during space expeditions or flights. However, evidence on how this affects the gut microbiota is limited. This study aimed to assess changes in the composition of gut microbiota in volunteers subjected to a 14-day stay in a controlled space-analogue habitat. Five adults provided stool samples at baseline and after two weeks. Meals were freeze-dried and standardized for portion size and composition. Meals were served according to a daily schedule with no additional snacks allowed. Coffee and tea were permitted. Compliance was monitored by returning and verifying the packaging. Bacterial community profiles were assessed using shallow shotgun metagenomics and analyzed using paired statistical methods, including alpha diversity indices and beta diversity ordination with permutation-based testing. Differential abundance analyses were performed to identify taxa showing trends toward change during the intervention. Overall gut bacterial diversity and community structure were essentially stable over 14 days among all participants. No statistically significant changes in alpha diversity were observed, and global beta diversity patterns did not indicate a consistent separation of the entire community between baseline and day 14. Exploratory analyses suggested small changes within individuals in the relative abundance of selected taxa; however, inter-individual variability prevailed, and the small sample size limited statistical power. It appears that a diet consisting entirely of freeze-dried foods, consumed for 14 days, did not significantly affect the overall diversity of the gut microbiota or the structure of its communities. However, these studies are preliminary in nature and provide hypotheses for use in larger, controlled studies aimed at elucidating the microbiome's response to dietary regimens based on freeze-dried products.