2025, Vol. 7, Issue 8, Part C

Background: Basal metabolic rate (BMR) represents the minimum energy required to sustain vital physiological functions, accounting for 60-70% of daily energy expenditure. Body composition, particularly fat-free mass, is a key determinant of BMR. Accurate assessment of BMR is essential for personalized nutrition and metabolic disorder management. Traditional BMR prediction equations often lack precision across diverse populations, leading to increased use of advanced tools such as bioelectrical impedance analysis (BIA). This study aimed to compare body composition by gender, investigate BMR relationships, and evaluate the influence of age, gender, BMI, and muscle mass on BMR.

Methods: A cross-sectional study was conducted at the Baghdad Nutrition Clinic between March and May 2025, involving 150 adults aged 18-65 undergoing nutritional assessment or weight management. Participants were systematically sampled every third patient after applying inclusion and exclusion criteria. Data collection included structured questionnaires, anthropometric measurements, and body composition analysis using the In Body 270 BIA device. Ethical approval and informed consent were obtained. Statistical analyses encompassed descriptive statistics, correlation assessments, and regression modeling to identify significant predictors of BMR.

Results: The study revealed significant gender differences in body composition, with males showing higher lean mass, skeletal muscle mass (SMM), and basal metabolic rate (BMR), while females had higher fat mass and BMI. BMR increased progressively with BMI and muscle score quartiles, reaching the highest values in obese and high-muscle-score groups. Although BMR and fat-free mass declined with age, these differences were not statistically significant. Correlation analysis showed that BMR was strongly associated with fat-free mass (r = 0.891), SMM (r = 0.864), and weight (r = 0.822). Regression analysis identified SMM, fat-free mass, skeletal muscle%, and male gender as the strongest positive predictors of BMR, while age had a negative effect.

Conclusions: This study confirms that BMR is chiefly influenced by skeletal muscle and fat-free mass, with notable gender differences. Males showed higher BMR due to greater muscle mass. Accurate body composition analysis is essential for reliable BMR estimation and individualized nutrition planning.