Gut microbiota mediated the curvilinear associations between dietary animal protein intake and bone mineral density in Chinese adults

Abstract

Dietary protein intake is closely related to bone health. It remains unclear how different dietary protein sources contribute to bone mass and how the gut microbiota affects these processes. This study investigated the relationships of dietary animal and plant protein intake with bone mineral density (BMD), and the mediating role of gut microbes in these associations. A total of 1,012 participants aged 18-64 years were recruited. Dietary protein intake was assessed using a food frequency questionnaire. BMD was measured by Dual-energy X-ray absorptiometry. Gut microbiota was analysed by 16S rRNA sequencing. The relationship of dietary protein intake with BMD and the mediating effects of gut microbes were detected. Dietary animal protein intake had inverted U-shaped relationships with BMD at lumbar spine, total hip and whole body (P < 0.050). Positive association was observed between them in the subpopulation with an intake level below 0.87 g/kg/day (sβ = 0.095 to 0.107, P < 0.050). In individuals with intake levels higher than the threshold, a linear downward trend was observed (P < 0.050). Dietary plant protein intake was inversely associated with the lumbar spine (sβ = -0.192, P = 0.002) and total hip (sβ = -0.173, P = 0.008) BMD. Eleven and two bacterial genera were associated with dietary animal and plant protein intake, respectively (q-value < 0.250). Lactococcus, Lactonifactor, Lachnoclostridium, Coprococcus_1 and Dialister together mediated 14.50%-18.66% of associations between dietary animal protein intake and BMD at the three skeletal sites. In conclusion, the threshold effect of dietary animal protein intake on BMD was partly explained by some gut microbes. Excessive dietary animal protein intake and general dietary plant protein intake might not have positive effects. These findings may provide important insights into the prevention and management of osteoporosis.