The effects of enteral tube feeding and parenteral nutrition on appetite sensations and food intake in health and disease

Enteral tube feeding (ETF) and parenteral nutrition (PN) are unphysiological methods of feeding. They may not elicit the cephalic phase response because part or all of the gastrointestinal tract is bypassed, nutrients are typically given in liquid form by a continuous infusion over many hours and often overnight while patients sleep. Work conducted in animals, healthy subjects and patients suggests that nutrients delivered as ETF or PN are less effective in relieving appetite sensations than food intake. Distressing appetite sensations may even occur despite the provision by artificial nutrition of sufficient nutrients to meet requirements. The energy provided by ETF and PN is largely additional to oral food intake in humans eating ad libitum, although the extent to which this occurs may decrease with time. There is a need to establish ways (e.g. nutritional, pharmacological, psychological) to suppress appetite sensations and food intake when eating is contraindicated, and to enhance them when weaning from artificial nutrition is desirable.