Intensive care doctors have long wondered: just how important is nutrition to the survival of the sickest hospital patients, and how much food do these patients need to maximise their chances of recovery?
Now new joint New Zealand and Australian research - the largest intensive care nutrition trial ever undertaken - has shed light on those key questions.
Current international guidelines require that patients in intensive care on life support are given extra calories to ensure that their energy intake matches energy expenditure.
They're fed through a nasogastric tube but specialists say that in reality, these patients typically receive less than 60 percent of the recommended daily food intake because of factors such as nausea, vomiting and the need for fasting before surgery.
The research involved 4000 patients, 1500 of them from New Zealand, who were admitted to intensive care units (ICUs) in both countries.
Half of the patients received an energy-dense nutrition (1.5 kcal/ml) with added fat and carbohydrate to boost their calorific intake by almost 48 percent. The others received the usual recommended 1.0 kcal/ml nutrition formula. Those getting the extra nutrition experienced no improved survival after 90 days, and nor did the extra calories improve other results such as support for organs or length of stay of the patient in the ICU or in hospital.
Patients getting the extra calories also experienced more vomiting and needed more drugs to treat the vomiting.
The study co-author, Paul Young of the Wellington Hospital intensive care department and of the Medical Research Institute of New Zealand, said the research showed "there's no real cause for concern if a patient doesn't meet their recommended daily 'goal' calorific amount".
"When patients are sick, they don't feel hungry and this research shows that if you feed them extra calories in order to boost their nutritional intake, the end result is that they are just more likely to vomit and, most significantly, no more likely to get better," Dr Young said.
Until now much time and effort has gone into interventions to try and achieve the calorie intake in ICUs, such as using medicines to aid stomach emptying, and inserting special feeding tubes, Dr Young said.
"This study suggests that these interventions are often unnecessary."
The researchers do not know for sure why the nutrition formula with more calories resulted in more vomiting, adding it may be that vomiting is the body's response to receiving more calories than needed, Dr Young said.
Auckland Hospital intensive care specialist Shay McGuinness said the findings would help improve patient care in critical care units worldwide.
"This TARGET study has shown that using higher energy feed to try to get the calculated goal amount of food absorbed by the patient does not improve important outcomes and may actually result in more feeding complications.
"As many of us know from personal experience when we are sick we often lose our appetite.
"Allowing critically ill patients to self-regulate how much food they absorb may well be a better approach to artificially trying to boost energy delivery."