Overweight is generally defined as having more body fat (adipose tissue) than is optimally healthy. Being overweight is a common condition, especially where food supplies are plentiful and lifestyles are sedentary. As much as 64% of the United States adult population is considered either overweight or obese, and this percentage has increased over the last four decades. A series of graphics from the Centers for Disease Control and Prevention (CDC) shows the trend in which the prevalence of obesity has increased in the U.S. during the past three decades: Obesity Epidemic: U.S. Temporal Trends 1985-2004 Excess weight has reached epidemic proportions globally, with more than 1 billion adults being either overweight or obese. 1 Increases have been observed across all age groups.

A healthy body requires a minimum amount of fat for the proper functioning of the hormonal, reproductive, and immune systems, as thermal insulation, as shock absorption for sensitive areas, and as energy for future use. But the accumulation of too much storage fat can impair movement and flexibility, and can alter the appearance of the body.

Classification

The degree to which a person is overweight is generally described by Body Mass Index. The range for overweight is a BMI of 25 to 29.9 with BMI's >= 30 classified as obesity. There are however several other common ways to measure the amount of adiposity or fat present in an individual's body.

• Body Mass Index

Body Mass Index, or BMI is a measure of a persons weight taking into account their height. It is given by the formula: BMI equals body weight divided by the square of the persons height; with weight in kilograms and height in meters. BMI numbers however are typically used and written as unitless numbers. BMI provides a significantly more accurate representation of body fat content than simply measuring a persons weight. It is highly correlated with both percentage of body fat and body fat mass. It does not take into account some factors such as pregnancy, bodybuilding, or children which effect body composition however is an accurate reflection of fat percentage in the majority of the adult population.

• Simple Weighing

The weight of the individual is measured and compared to an estimated ideal weight. This is the easiest and most common method, but by far the least accurate, as it only measures one quantity (weight) and often does not take into account many factors such as height, body type, and relative amount of muscle mass.

• Skinfold Calipers or "pinch test"