Not all body fat carries the same health risk. Visceral fat, stored around internal organs in the abdominal cavity, behaves differently from subcutaneous fat stored elsewhere under the skin: it's more metabolically active, more strongly associated with insulin resistance and inflammation, and more predictive of cardiovascular and metabolic disease risk. Two people with identical body weight or BMI can have very different visceral fat levels and correspondingly different aging-related risk profiles.
That's why body composition measurement (via DEXA scan, waist circumference, or MRI-based fat mapping) has become a more clinically meaningful biomarker than body weight or BMI alone for tracking metabolic aging. This connects directly to the glucose regulation entry in this directory: visceral fat is a major driver of the insulin resistance that glucose-regulation markers are measuring the downstream effects of.
Of the biomarkers tracked in this directory, visceral fat is among the most directly actionable through diet and exercise, similar to glucose regulation and VO2 max, giving readers a biomarker category that's both well-validated in the clinical literature and genuinely within their own influence.