Medical Causes

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.