Body fat is not one thing. A layer of fat under the skin around the hips and thighs sits quietly, while a separate depot packed deep in the abdomen behaves almost like an endocrine organ and drives a large share of the risk usually attributed to weight itself.
That difference matters even for people who look lean.
The National Heart, Lung, and Blood Institute flags waist size as a warning sign that is separate from overall weight. In its guidance, a waist above 40 inches in men or above 35 inches in women signals elevated risk.
The reason, the agency notes, is that if most fat is around the waist rather than the hips, the risk of heart disease and type 2 diabetes rises.
Also read: The foods with actual clinical evidence for easing period cramps and fatigue
Why organ fat behaves differently
Subcutaneous fat, the pinchable layer under the skin, is largely a storage tissue. Visceral fat sits deeper, lining the abdominal walls and wrapping many internal organs, including the liver, stomach and intestines.
In Cleveland Clinic's patient guidance, excess visceral tissue is tied to cardiovascular disease, higher cholesterol, atherosclerosis and metabolic syndrome.
The mechanism is anatomical as much as metabolic. A 2024 review in the peer-reviewed literature describes visceral fat as directly draining into the portal vein, meaning its output reaches the liver before the rest of the body.
The review reports that secretion of proinflammatory cytokines, including interleukin-6, interleukin-8 and macrophage chemoattractant protein-1, is higher in this depot than in subcutaneous fat.
Also read: Nearly half of Americans fall short on magnesium. 8 signs you may be one of them
Those signaling molecules, together with free fatty acids released from visceral cells, are thought to drive fat accumulation, insulin resistance, inflammation and fibrosis in the liver, a chain that pushes up glucose and triglyceride levels systemically.
That is why the same waist measurement can mean very different things depending on where the fat sits, and why body mass index alone can be misleading.
The mortality signal separate from weight
The link is not only to disease markers. A 2022 systematic review in Frontiers in Endocrinology pooled CT-based studies of visceral adipose tissue and death from any cause. In cohorts with a mean age of 65 or younger, higher visceral fat was tied to an 11 to 98 percent increase in relative all-cause mortality risk per increment of visceral fat area or volume, across studies ranging from 291 to more than 34,000 participants.
The authors note the effect weakened after adjusting for glucose markers, body mass index or other fat parameters, which fits the broader picture that visceral fat mediates much of the risk that gets attributed to weight itself.
Also read: A bowl of cottage cheese before bed can replace a casein shake, small trial suggests
An earlier landmark analysis of 291 men, published in the journal Obesity, similarly found that visceral fat alone independently predicted mortality risk after adjustment for other fat measures, based on CT imaging and a mean follow-up of about 2.2 years.
The encouraging part
The metabolic activity that makes visceral fat dangerous also makes it responsive. Research pooled in a 2025 dietary intervention study reported in Frontiers in Endocrinology found that visceral adiposity loss is associated with improvement in cardiometabolic markers, and separate weight-loss guidance from Johns Hopkins notes that modest reductions in total body weight, on the order of 5 to 10 percent, translate into disproportionately larger drops in the visceral depot specifically.
For anyone concerned about a rising waistline, checking with a doctor and having waist circumference measured is a more useful screen than the bathroom scale. The number that predicts heart and metabolic risk most reliably is not how much weight is on the body, but how much of it is hiding around the organs.
Also read: Forget the 10,000-step rule: 7,000 a day delivers most of the health payoff
Also read: Morning workouts helped sleep and body fat, evening workouts helped blood vessels