Therapy-related
Medical treatment can directly or indirectly cause weight loss, impairing treatment effectiveness and recovery that can lead to further weight loss in a vicious cycle. Many patients will be in pain and have a loss of appetite after surgery. Part of the bodys response to surgery is to direct energy to wound healing, which increases the bodys overall energy requirements. Surgery affects nutritional status indirectly, particularly during the recovery period, as it can interfere with wound healing and other aspects of recovery. Surgery directly affects nutritional status if a procedure permanently alters the digestive system. Enteral nutrition (tube feeding) is often needed. However a policy of nil by mouth for all gastrointestinal surgery has not been shown to benefit, with some weak evidence suggesting it might hinder recovery. Early post-operative nutrition is a part of Enhanced Recovery After Surgery protocols. These protocols also include carbohydrate loading in the 24 hours before surgery, but earlier nutritional interventions have not been shown to have a significant impact. 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.Loss of hope, status or social contact and spiritual distress can cause depression, which may be associated with reduced nutrition, as can fatigue.
Myths
Some popular beliefs attached to weight loss have been shown to either have less effect on weight loss than commonly believed or are actively unhealthy. According to Harvard Health, the idea of metabolic rate being the "key to weight" is "part truth and part myth" as while metabolism does affect weight loss, external forces such as diet and exercise have an equal effect. They also commented that the idea of changing ones rate of metabolism is under debate. Diet plans in fitness magazines are also often believed to be effective but may actually be harmful by limiting the daily intake of important calories and nutrients which can be detrimental depending on the person and are even capable of driving individuals away from weight loss. Health effects
Obesity increases health risks, including diabetes, cancer, cardiovascular disease, high blood pressure, and non-alcoholic fatty liver disease, to name a few. Reduction of obesity lowers those risks. A 1-kg loss of body weight has been associated with an approximate 1-mm Hg drop in blood pressure. Intentional weight loss is associated with cognitive performance improvements in overweight and obese individuals. See also
Anorexia
Cigarette smoking for weight loss
Dieting
Physical exercise
Weight gain

References
External links

Weight loss  at Curlie
Health benefits of losing weight By IQWiG at PubMed Health
Weight-control Information Network Archived 12 February 2015 at the Wayback Machine  U.S. National Institutes of Health
Nutrition in cancer care By NCI at PubMed Health
Unintentional weight loss