Abstract

Being overweight is having more body fat than is optimally healthy. Being overweight is especially common where food supplies are plentiful and lifestyles are sedentary.

Excess weight has reached epidemic proportions globally, with more than 1 billion adults being either overweight or obese in 2003. In 2013 this increased to more than 2 billion. Increases have been observed across all age groups.

A healthy body requires a minimum amount of fat for 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, flexibility, and alter the appearance of the body.

Classification

The degree to which a person is overweight is generally described by the body mass index (BMI). "Overweight" is defined as a BMI of 25 or more, thus it includes pre-obesity defined as a BMI between 25 and 30 and obesity as defined by a BMI of 30 or more. Pre-obese and overweight however are often used interchangeably, thus giving overweight a common definition of a BMI of between 25–30. 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 volume index

- Simple weighing

- Skinfold calipers or "pinch test"

- Bioelectrical impedance analysis

- Hydrostatic weighing

- Dual-energy X-ray absorptiometry (DEXA)

The most common method for discussing this subject and the one used primarily by researchers and advisory institutions is BMI. Definitions of what is considered overweight vary by ethnicity. The current definition proposed by the US National Institutes of Health (NIH) and the World Health Organization (WHO) designates whites, Hispanics and blacks with a BMI of 25 or more as overweight. For Asians, overweight is a BMI between 23 and 29.9 and obesity for all groups is a BMI of 30 or more.

BMI, however, does not account extremes of muscle mass, some rare genetic factors, the very young, and a few other individual variations. Thus it is possible for an individuals with a BMI of less than 25 to have excess body fat, while others may have a BMI that is significantly higher without falling into this category. Some of the above methods for determining body fat are more accurate than BMI but come with added complexity.

If an individual is overweight and has excess body fat it can create or lead to health risks. Reports are surfacing, however, that being mildly overweight to slightly obese – BMI being between 24 and 31.9 – may be actually beneficial and that people with a BMI between 24 and 31.9 could actually live longer than normal weight or underweight persons.

Health effects

While the negative health outcomes associated with obesity are accepted within the medical community, the health implications of the overweight category are more controversial. The generally accepted view is that being overweight causes similar health problems to obesity, but to a lesser degree. A 2016 review estimated that the risk of death increases by seven percent among overweight people with a BMI of 25 to 27.5 and 20 percent among overweight people with a BMI of 27.5 to 30. The Framingham heart study found that being overweight at age 40 reduced life expectancy by three years. Being overweight also increases the risk of oligospermia and azoospermia in men.

Katherine Flegal et al., however, found that the mortality rate for individuals who are classified as overweight (BMI 25 to 30) may actually be lower than for those with an "ideal" weight (BMI 18.5 to 25).

Being overweight has been identified as a cause of cancer, and is projected to overtake smoking as the primary cause of cancer in developed countries as cases of cancer linked to smoking dwindle.

Psychological well-being is also at risk in the overweight individual due to social discrimination. However, children under the age of eight are normally not affected.

Being overweight has been shown not to increase mortality in older people: in a study of 70 to 75-year old Australians, mortality was lowest for "overweight" individuals (BMI 25 to 30), while a study of Koreans found that, among those initially aged 65 or more, an increase in BMI to above 25 was not associated with increased risk of death.

Causes

Being overweight is generally caused by the intake of more calories (by eating) than are expended by the body (by exercise and everyday activity). Factors that may contribute to this imbalance include:

- Alcoholism

- Eating disorders (such as binge eating)

- Genetic predisposition

- Hormonal imbalances (e.g. hypothyroidism)

- Insufficient or poor-quality sleep

- Limited physical exercise and a sedentary lifestyle

- Poor nutrition

- Metabolic disorders, which could be caused by repeated attempts to lose weight by weight cycling

- Overeating

- Psychotropic medication (e.g. olanzapine)

- Smoking cessation and other stimulant withdrawal

- Stress

People who have insulin dependant diabetes and chronically overdose insulin may gain weight, while people who already are overweight may develop insulin tolerance, and in the long run develop type II diabetes.

Treatment

The usual treatments for overweight individuals is diet and physical exercise.

Dietitians generally recommend eating several balanced meals dispersed through the day, with a combination of progressive, primarily aerobic, physical exercise.

Because these general treatments help most case of obesity, they are common in all levels of overweight individuals.

Epidemiology

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.