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 body's response to surgery is to direct energy to wound healing, which increases the body's 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 suggestion 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.
Some medications can cause weight loss, while others can cause weight gain.
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.