Body composition

What is body composition, and how is it measured?

Beyond BMI, metrics such as skeletal muscle, fat mass, and visceral fat give deeper insight into nutrition and disease risk, and choosing an assessment method means balancing cost, practicality, accuracy, and data quality [1]. Measurement ranges from simple anthropometry, a tape measure or scale, to techniques such as bioelectrical impedance analysis, DXA, CT, and MRI, since anthropometry alone gives unreliable estimates of fat mass and its distribution compared with these methods [2]. A 2025 Lancet Commission recommends confirming excess body fat with a direct measurement, or with a body measure such as waist circumference, in addition to BMI [3].

How does body composition change with GLP-1 weight loss?

A 2026 systematic review of 35 studies found that weight loss from incretin-based medications was consistently linked to lower total fat mass and visceral fat, with a median 28.3% of total weight loss attributable to muscle-based measures; the review found body composition methods varied too much across studies to combine into a single estimate [4].