Two depots, not one
Fat under the skin is the fat that can be pinched. Visceral fat sits within the abdominal cavity, packed around and between the organs, and cannot be. A third category, sometimes called ectopic fat, refers to fat accumulating inside organs that are not designed as storage — most importantly the liver, and also muscle.
The position statement literature treats these as distinct rather than as more and less of the same thing, and reviews the evidence that they differ in their association with atherosclerosis and cardiometabolic disease. That distinction is the whole reason a waistline is measured at all instead of relying on the scale.
Sources: [1]
Why position appears to matter
The mechanisms are still being argued about, and it is worth saying so plainly rather than presenting a tidy causal story. What is reasonably established is the association: greater visceral and ectopic fat is associated with the metabolic abnormalities that show up on a panel, and this association persists after accounting for overall body fatness.
Fat in the liver is the clearest worked example. Reviews of the relationship between liver fat, visceral fat and insulin sensitivity describe them as closely intertwined, and describe the difficulty of establishing which drives which. Anyone offering a confident causal sequence for an individual is going beyond the evidence.
Association is not the same as cause, and the direction of the relationship between these depots and metabolic change is genuinely unsettled in the literature.
How it is actually detected
Properly, by imaging — a CT or MRI cross-section quantifies the depots directly, and that is the reference method used in the research these conclusions come from. It is not a routine clinical test, it is not cheap, and it is not something to seek out on the basis of a worry.
In practice, waist circumference is the proxy, which is why the consensus argument is for measuring it routinely alongside body-mass index. It is imperfect, it cannot separate the depots, and it is available to everybody with a tape measure, which is a trade the evidence supports making.
What about the body composition machine at the gym
Bioelectrical impedance devices — the scales and handheld units that print a visceral fat rating — estimate body composition by passing a small current and modelling the result. They are convenient, and their output for abdominal fat specifically is an estimate derived from a model rather than a measurement of the depot.
The readings are also sensitive to hydration, to when you last ate and drank, and to when you last exercised. Used consistently, at the same time of day on the same device, the trend can be mildly informative. Treated as a measurement of the fat around your organs, the printed number promises more than the method can deliver.
Sources: [3]
The liver is where this stops being abstract
Fat accumulating in the liver is common, is frequently found incidentally on an abdominal ultrasound done for something else, and is closely associated with the same metabolic picture. It is also the reason liver enzymes appear on a metabolic panel that otherwise looks like it is about sugar.
One important caveat travels with that: liver enzymes are an insensitive way to detect fat in the liver, and normal enzymes do not exclude it. So a normal liver function test is reassuring about liver injury and is not a clean bill of health for the depot, which is exactly the kind of distinction a report does not make and a clinician does.
Sources: [2]
Why this lands harder in India
The body-composition evidence discussed elsewhere on this site points in one direction: at a given body-mass index, South Asian populations tend to carry a higher proportion of fat and more of it abdominally. That means the depot most strongly associated with metabolic abnormality is over-represented at weights the international charts describe as unremarkable.
India's national metabolic survey found abdominal obesity alongside prediabetes and lipid abnormalities at a scale consistent with that. The conclusion is not that everyone should worry about a word they read on the internet; it is that the tape measure and the panel are doing more work here than the bathroom scale, and neither of them is what most people check.