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The Role of Protein in Critically Ill Patients

Value of protein in critically ill patients

In general, adequate nutrition is not just the provision of calories. In fact, a balanced supply of different macro- and micronutrients is needed to maintain a good state of health.1This is especially true for critically ill patients.

Critically ill adult patients, particularly those who suffer from catabolic stress, have specific nutritional requirements, namely for high protein and lower energy.234567 Due to their increased metabolic rate, protein breakdown exceeds synthesis, which is accompanied by rapid loss of muscle mass. 8910

An adequate provision of protein through nutritional therapy may help to stimulate protein synthesis 11 and counteract muscle wasting. 111213

Consequences of protein deficit
Critically ill patients may lose up to 850 g/day of muscle mass, particularly in the first 5 days of ICU stay.14 This may have severe consequences, especially in long-stay patients who may experience more severe cumulative energy and protein deficits, affecting morbidity, as well as mortality.1516

Figure 1: Impact of decreasing body mass on patient outcomes1718

The role of adequate protein supply in critically ill patients

High amounts of protein may be vital for critically ill patients to maintain as much lean body mass as possible and to support physical function and recovery.12 An observational study has shown that receiving at least 80 percent of the prescribed protein target (1.2 g/kg/d) was associated with better survival, and a decreased time until patients were discharged alive.19


Nutritional support for critically ill patients must consider the specific metabolic changes which occur in these patients, resulting in a requirement for:

  • High amounts of amino acids, due to the increased demand of synthesizing glucose and acute phase proteins required for healing and recovery.31115202122 It has been shown that provision of high quantities of protein may help to counteract loss of lean body mass during critical illness. 121323
  • Adequate amounts of exogenous energy, to compensate for prevalent insulin resistance, whilst mediating risk of hyperglycaemia .212425
  • Adequate amounts of glucose and lipids to reduce the risk of hyperglycaemia and hypertriglyceridemia.25


The optimal strategy for critically ill patients is to provide moderate amounts of energy and high amounts of protein in the beginning, and more energy and high amounts of protein subsequently. Early protein intake, of e.g. at least 1.2 g/kg/d starting day 4 of ICU admission, may be associated with lower mortality in non-septic, critically ill patients. 26


Although the benefits of protein provision and the consequences of protein deficit in critically ill patients are well known, protein deficit is still prevalent. A recent observational study looked at caloric and protein deficits in Latin America. During the “Screening Day Latin America”, critically ill patients were screened to measure their current nutritional status. 47.6 percent of Latin American hospital patients still fail to meet >90 percent of their protein targets. 27