Statistical methods
SECONDARY
The microbial analyses were secondary objectives of the original trial, and the sample size calculation was not based on detecting significant changes in either gut microbiota abundance, body composition parameters or iron status markers. In brief, the sample size was based on urinary C-telopeptide of type II collagen (CTX-II)/creatinine and serum cartilage oligomeric matrix protein (COMP) as the primary outcomes of the study. The sample size was calculated to detect a 20 % difference between the groups using the standard deviation from the latest lab result. For urinary CTX-II/creatinine a sample size of 60 and for serum COMP a sample size of 17 were required to detect a 20 % difference between groups with a power of 95 %. The serum COMP required a small sample size, thus the average of two outcomes was used for the sample size of 48 (