PermiT underfeeding?

High calorie intake on ICU has long been known to be a bad idea. Topping up early enteral feeding deficits with parenteral nutrition is now felt to be non-life-saving and possibly dangerous. Animal studies have suggested that it is the protein element of feeding that keeps the mitochondria happy, not calories per se.

So, the PermiT study, a refocussed repeat of a previous trial, was designed to answer the question of whether targeting protein delivery but forgoing some calories would be beneficial in the critically ill.This was an unblinded, pragmatic RCT in Canada and Saudi Arabia on around 900 mixed specialty critically ill patients.

For 14 days, half were given 40-60% of the (Penn-State) calculated calorie requirement, and the others were given 70-100%. Both had 1.2-1.5g/Kg of protein each day and some multivitamins. Almost all was given enterally.

There was no difference between the 2 groups in primary end-point 90 day mortality, or any secondary outcome (28, 90 or 180 day morality, or ventilator-free days).Underfed

Interestingly, post-hoc analysis showed a lower fluid balance and less use of renal support in the underfed.



Reasons you should hesitate to form a strong opinion based on this are:

  • The randomised patients comprised just 14% of the potential eligible group.
  • The duration of intervention was 14 days. Nutrition after this was not controlled.
  • Low number of surgical patients.
  • Very low use of parenteral nutrition.


These weaknesses aside, this work adds weight to the growing refinement of calorie/protein/route feeding in the critically ill. Underfed but sufficiently fed (‘satisfed!’)? Perhaps we shouldn’t struggle too hard to get the calories in. And should we consider separating our feeding constituents and prioritising the protein?


1 ping

  1. LITFL Review 186 | LITFL: Life in the Fast Lane Medical Blog

    […] a great review of the recent PermiT trial looking at reduced calorie intake in critically ill patients. Thanks, Justin! […]

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