To investigate the correlation of skeletal muscle index (SMI) with obesity and osteoporosis, and to explore the changes of intestinal microflora in different SMI aged patients with sarcopenia.

Totally 103 aged patients with sarcopenia were divided into the low SMI group (38 males, 11 females) and very low SMI group (43 males, 11 females) according to the mean SMI (male: 5.1 kg / m², female: 4.3 kg / m²). The SMI, body mass index (BMI), total body fat percentage, hip density and femoral neck density were measured, and the correlation between SMI and above indicators was analyzed by the Pearson test. Mean-while, the intestinal microflora was detected by PCR.

In aged male patients, the levels of SMI[(4.4 ± 0.5) kg / m² vs. (5.8 ± 0.5) kg / m²] and BMI [(21.6 ± 2.9) kg / m² vs. (24.8 ± 3.1) kg / m²] in the very low SMI group were much lower than those in the low SMI group (t = 12.062, P < 0.001; t = 4.740, P < 0.001). In aged female patients, only the SMI level in the very low SMI group was much lower than that in the low SMI group [(3.8 ± 0.3) kg / m² vs. (4.8 ± 0.8) kg / m², t = 7.065, P < 0.001]. Meanwhile, in aged male patients, the SMI was positively correlated with BMI (r = 0.521, P < 0.001), and the contents of Faecali-bacterium prausnitzii [2.87 (0.42, 10.86) × 10⁶ copies / g vs. 9.57 (1.33, 36.04) × 10⁶ copies / g] and Clostridium cluster I [3.03 (0.39, 20.47) × 10⁴ copies / g vs. 15.94 (3.57, 48.88) × 10⁴ copies / g] in the very low SMI group were much lower than those in the low SMI group (Z = 1.987, P = 0.047; Z = 2.943, P = 0.003). In aged female patients, the SMI was negatively correlated with total body fat percentage (r = -0.447, P = 0.029), and compared with the low SMI group, the content of Enterococcus decreased [2.56 (0.20, 54.82) × 10⁴ copies / g vs. 0.28 (0.01, 1.55) × 10⁴ copies / g, Z = 2.068, P = 0.040], and the content of Clostridium cluster I increased significantly [1.18 (0.37, 11.73) × 10⁴ copies / g vs. 16.88 (5.22, 66.79) × 10⁴ copies / g, Z = 2.134, P = 0.034].

The SMI is related to the BMI and total body fat percentage in elderly patients with sarcopenia, and the content of intestinal microflora varies with different SMI degrees.