Weight loss, in the context of medicine, health, or physical fitness is a reduction of the total body mass, due to a mean loss of fluid, body fat or adipose tissue and/or lean mass, namely bone mineral deposits, muscle, tendon, and other connective tissue. It can occur unintentionally due to an underlying disease or can arise from a conscious effort to improve an actual or perceived overweight or obese state. Intentional weight loss is commonly referred to as slimming.

Characteristics

Unintentional weight loss may be a result of loss of fat, muscle atrophy, fluid loss or a combination of these. It is generally regarded as a medical problem when at least 10% of a person's body weight has been lost in six months or 5% in the last month.Another criterion used for assessing weight that is too low is the body mass index (BMI). However, even lesser amounts of weight loss can be a cause for serious concern in a frail elderly person.

Weight loss issues related to specific diseases include:

As chronic obstructive pulmonary disease (COPD) advances, about 35% of patients experience severe weight loss called pulmonary cachexia, including diminished muscle mass. Around 25% experience moderate to severe weight loss, and most others have some weight loss.[7] Greater weight loss is associated with poorer prognosis. Theories about contributing factors include appetite loss related to reduced activity, additional energy required for breathing, and the difficulty of eating with dyspnea (labored breathing).

Cancer, a very common and sometimes fatal cause of unexplained (idiopathic) weight loss. About one-third of unintentional weight loss cases are secondary to malignancy. Cancers to suspect in patients with unexplained weight loss include gastrointestinal, prostate, hepatobillary (hepatocellular carcinoma, pancreatic cancer), ovarian, hematologic or lung malignancies.

Social conditions

Social conditions such as poverty, social isolation and inability to get or prepare preferred foods can cause unintentional weight loss, and this may be particularly common in older people. Nutrient intake can also be affected by culture, family and belief systems. Ill-fitting dentures and other dental or oral health problems can also affect adequacy of nutrition

Therapeutic weight loss techniques

The least intrusive weight loss methods, and those most often recommended, are adjustments to eating patterns and increased physical activity, generally in the form of exercise. The World Health Organization recommended that people combine a reduction of processed foods high in saturated fats, sugar and salt[29] and caloric content of the diet with an increase in physical activity.

An increase in fiber intake is also recommended for regulating bowel movements.

Other methods of weight loss include use of drugs and supplements that decrease appetite, block fat absorption, or reduce stomach volume.

Bariatric surgery may be indicated in cases of severe obesity. Two common bariatric surgical procedures are gastric bypass and gastric banding.Both can be effective at limiting the intake of food energy by reducing the size of the stomach, but as with any surgical procedure both come with their own risks that should be considered in consultation with a physician.

Weight loss industry

There is a substantial market for products which promise to make weight loss easier, quicker, cheaper, more reliable, or less painful. These include books, DVDs, CDs, cremes, lotions, pills, rings and earrings, body wraps, body belts and other materials, fitness centers, personal coaches, weight loss groups, and food products and supplements.

In 2008 between US$33 billion and $55 billion was spent annually in the US on weight-loss products and services, including medical procedures and pharmaceuticals, with weight-loss centers taking between 6 and 12 percent of total annual expenditure. Over $1.6 billion a year was spent on weight-loss supplements. About 70 percent of Americans' dieting attempts are of a self-help nature. Although often short-lived, these diet fads are a positive trend for this sector as Americans ultimately turn to professionals to help them meet their weight loss goals.