The Effect of Chitosan Supplementation on the Gut Microbiota and Various Health Factors in Icelandic Females: A Placebo‐Controlled, Double‐Blind, Randomized Trial

ABSTRACT Chitosan is suggested to have prebiotic properties, yet clinical evidence on its in vivo effects on the human gut microbiota and various health factors remains scarce. This study aimed to evaluate the effects of chitosan supplementation on gut microbiota composition and various health factors in Icelandic females. Sixty Icelandic females (aged 26–70; BMI 19.1–35.0 kg/m 2 ) were randomized to a 12‐week intervention receiving either 3 g/day of encapsulated chitosan (LipoSan Ultra) (TRG, n = 28) or placebo (PLG, n = 32). Anthropometrics, health factors, endurance, and health status questionnaires were collected at baseline (T1) and post‐intervention (T3). All values remained within reference ranges at both timepoints in both groups, except weight, waist circumference, and fat mass, which were above. In TRG, alkaline phosphatase (ALP) levels increased, and fecal consistency shifted toward constipation. 16S rRNA microbial analysis showed decreased diversity/evenness, increased T1–T3 separation by nonmetric multidimensional scaling, and higher Actinobacteriota abundance. Genus level shifts included reduced Blautia, Eubacterium hallii , CAG‐56 levels and increased Ruminococcus gnavus, Clostridium innocuum, Bifidobacterium , and Holdemania . This novel clinical study demonstrates that 12 weeks of chitosan supplementation alters gut microbiota composition without affecting general health status in females. Trial Registration This trial was registered at Clinicaltrials.gov as NCT04551365