The influence of dietary protein intake on body composition, bone health, and circulating cytokines in adults with obesity

Abstract

Obesity is associated with altered body composition and increased fracture risk, challenging prior assumptions that excess adiposity provides skeletal protection. Emerging evidence suggests that dietary protein intake and cytokine activity may influence musculoskeletal health, yet limited research has examined these associations specifically in adults with obesity. This cross-sectional study evaluated the relationships among dietary protein intake, including animal and plant sources, body composition, bone mineral density (BMD), and select circulating cytokines in individuals with obesity. Eighty-seven adults (mean age 49 ± 11 years; body mass index 37.0 ± 6.0 kg/m²) were assessed for dietary intake via 3-day food records, body composition by dual-energy X-ray absorptiometry, and plasma concentrations of osteocalcin and cytokines (adiponectin, leptin, irisin, myostatin). Participants consuming ≥1.0 g/kg/day protein had significantly lower body fat mass (45 ± 7% vs. 49 ± 7%), higher lean mass (52 ± 6% vs. 48 ± 7%), and greater intake of energy, fat, carbohydrate and select micronutrients (thiamine, vitamin D, niacin, vitamin B12, sodium, potassium, magnesium, phosphorus, and calcium) compared to those consuming <1.0 g/kg/day. No significant differences were observed between groups in visceral adipose tissue, adipokines, total body BMD, or osteocalcin. However, a trend toward higher plasma irisin and myostatin concentrations was observed in participants with higher protein intake, with elevated plasma irisin in those with greater animal protein consumption. Furthermore, irisin levels were positively correlated with total body BMD (r =0.339). These findings highlight the importance of higher protein intake, beyond the Recommended Dietary Allowance of 0.8 g/kg/d, in supporting lean mass in individuals with obesity. Future research is needed to clarify the role of irisin and other cytokines with dietary protein intake, body composition, and bone health in individuals with obesity.