What Is Belly Fat?

Abdominal obesity, colloquially known as belly fat or clinically as central obesity, is the accumulation of visceral fat resulting in an increase in waist size. There is a strong correlation between central obesity and cardiovascular disease.

Visceral fat, also known as organ fat or intra-abdominal fat, is located inside the peritoneal cavity, packed in between internal organs and torso, as opposed to subcutaneous fat which is found underneath the skin, and intramuscular fat which is found interspersed in skeletal muscle. Visceral fat is composed of several adipose depots including mesenteric, epididymal white adipose tissue (EWAT) and perirenal depots. An excess of visceral fat is known as central obesity, the "pot belly" or "beer belly" effect, in which the abdomen protrudes excessively. This body type is also known as "apple shaped", as opposed to "pear shaped", in which fat is deposited on the hips and buttocks.

Causes

The immediate cause of obesity is net energy imbalance--the organism consumes more usable calories than it expends, wastes, or discards via elimination. The fundamental cause of obesity is not well understood, but is presumably a combination of the organism's genes and environment. The specific cause of central distribution of fat is also not well understood.

In humans, central obesity is correlated with overeating and a sedentary lifestyle. Hypercortisolism, such as in Cushings syndrome also leads to central obesity. Many prescription drugs can also have side effects resulting in obesity.

Diagnosis

While central obesity can be obvious just by looking at the naked body (see the picture), the severity of central obesity is determined by taking waist and hip measurements. The absolute waist circumference (>102 centimetres (40 in) in men and >88 centimetres (35 in) in women) and the waist-hip ratio (>0.9 for men and >0.85 for women) are both used as measures of central obesity. A differential diagnosis includes distinguishing central obesity from ascites and intestinal bloating. In the cohort of 15,000 people participating in the National Health and Nutrition Examination Survey (NHANES III), waist circumference explained obesity-related health risk better than the body mass index (or BMI) when metabolic syndrome was taken as an outcome measure and this difference was statistically significant. In other words, excessive waist circumference appears to be more of a risk factor for metabolic syndrome than BMI.

An increasing acceptance of the importance of central obesity within the medical profession as an indicator of health risk has led to new developments in obesity diagnosis such as the Body Volume Index, which measures central obesity by measuring a person’s body shape and their weight distribution

BVI is based upon the principle that excess abdominal weight, measured by part volume as a percentage of total volume, constitutes a greater health risk. Recent validation has concluded that total and regional body volume estimates correlate positively and significantly with biomarkers of cardio-vascular risk and BVI calculations correlate significantly with all biomarkers of cardio-vascular risk.