**3. Results**

#### *3.1. Characteristics of the Study Population*

Thirty-five participants were included in the study: 18 older adults with PF&S (mean age 75.5 ± 3.9 years; 56.0% women) and 17 nonPF&S controls (mean age 73.9 ± 3.2 years; 29.0% women). Clinical and demographic characteristics of study participants are presented in Table 3. Age, sex distribution, and number of co-morbid conditions and medications did not differ between groups. Participants with PF&S showed higher BMI than nonPF&S controls.

**Table 3.** Main characteristics of study participants according to the presence of physical frailty & sarcopenia (PF&S).


Abbreviations: aLM: appendicular lean mass; BMI: body mass index; PF&S: physical frailty & sarcopenia; nonPF&S: nonphysically frail, nonsarcopenic; SD: standard deviation; SPPB: short physical performance battery. \* Includes hypertension, coronary artery disease, prior stroke, peripheral vascular disease, diabetes, chronic obstructive pulmonary disease, and osteoarthritis. \*\* Includes prescription and over-the-counter medications.

#### *3.2. Features of Gut Microbiota According to the Presence of PF&S*

No differences in microbial alpha diversity were determined between PF&S and nonPF&S participants (Figure 1).

**Figure 1.** Chao1 index of gu<sup>t</sup> microbial alpha diversity in participants with PF&S and in nonPF&S controls.

The analysis of the differential abundance of microbial taxa between PF&S and nonPF&S groups at the phylum, family, and genus levels showed an increase in Peptostreptococcaceae (*p* = 0.008 Table S1) and Bifidobacteriaceae (*p* = 0.013) at the family level and of *Dialister* (*p* = 0.028), *Pyramidobacter* (*p* = 0.043), and *Eggerthella* (*p* = 0.05) at the genus level, and a depletion in *Slackia* (*p* < 0.0001) and *Eubacterium* (*p* = 0.028) in PF&S participants (Figure 2). No significant differences in the relative abundance of intestinal bacteria phyla were found between groups.

**Figure 2.** Comparison of gut microbiota relative abundance at the phylum (left panel, blue), family (middle panel, orange), and genus (right panel, green) levels between participants with PF&S and nonPF&S controls. Comparisons with a negative log2 fold change (log2FC) are represented in grey. Only comparisons with a log2FC higher or lower than ± 1.5 and an adjusted *p* value < 0.05 are considered significant (\*).
