Two depots with different jobs
Subcutaneous fat sits just under the skin and makes up the majority of body fat; it is largely a storage and insulation depot and is mostly a matter of appearance. Visceral fat is the deeper fat packed around the abdominal organs. The two behave differently: visceral fat is more metabolically active and releases fatty acids and signaling molecules into the portal circulation that drains to the liver.
Because of that anatomy and activity, excess visceral fat associates more strongly with insulin resistance, abnormal blood lipids, and cardiovascular risk than subcutaneous fat does.
Estimating and reducing it
Visceral fat is hidden from view, so a large waist can signal it even at a seemingly normal weight. Waist circumference and waist-to-height ratio are simple proxies, while imaging measures it directly. Encouragingly, visceral fat tends to respond well to overall fat loss through diet and physical activity, often dropping early in a successful effort.
These are population-level associations, not individual guarantees. This is general educational information, not medical advice.