Weight loss, in the context of medicine, health, or physical fitness, refers to a reduction of the total body mass, due to a mean loss of fluid, body fat or adipose tissue or lean mass, namely bone mineral deposits, muscle, tendon, and other connective tissue. Weight loss can either occur unintentionally due to malnourishment or an underlying disease or arise from a conscious effort to improve an actual or perceived overweight or obese state. “Unexplained” weight loss that is not caused by reduction in calorific intake or exercise is called cachexia and may be a symptom of a serious medical condition. Intentional weight loss is commonly referred to as slimming.
Impaired intake Poor appetite can be a direct symptom of an illness, or an illness could make eating painful or induce nausea. Illness can also cause food aversion.
Inability to eat can result from: diminished consciousness or confusion, or physical problems affecting the arm or hands, swallowing or chewing. Eating restrictions may also be imposed as part of treatment or investigations. Lack of food can result from: poverty, difficulty in shopping or cooking, and poor quality meals.
Impaired digestion &/or absorption This can result from conditions that affect the digestive system.
Altered requirements Changes to metabolic demands can be caused by illness, surgery and organ dysfunction.
Excess nutrient losses Losses from the gastrointestinal can occur because of symptoms such as vomiting or diarrhea, as well as fistulae and stomas. There can also be losses from drains, including nasogastric tubes.
Other losses: Conditions such as burns can be associated with losses such as skin exudates.
Permanent weight loss
In order for weight loss to be permanent, changes in diet and lifestyle must be permanent as well. Short-term dieting has not been shown to produce either long term weight loss or better health, and may even be counterproductive.