Only at the upper extremes of the body composition distribution, health risk increases significantly. In men and women, obesity is related to body mass index, abdominal circumference, and total skinfold thickness. Body mass index, as an expression of fatness, is positively related to excess mortality. Obesity increases blood volume and cardiac output while increasing left ventricular work and heart weight. Hypertrophy of the ventricles, particularly the left ventricle, seems to increase in proportion to the degree of obesity.
Hyperlipidemia is another risk factor associated with obesity.
The amount of subcutaneous fat has been found to have a significant association with HDL cholesterol in serum. It has been proposed that chronic hyperinsulinemia is largely responsible for hunger, cravings and weight gain observed in many obese. This has been attributed to the frequent failures of diet and behavioral modification programs. Epidemiological evidence and animal experimentation support the role of chronic hyperinsulinemia as a major factor in obesity. This cycle maintains excess fat and can override attempts of dietary and behavioral intervention.