Permissive underfeeding in critical illness

What the study found

The PermiT trial (New England Journal of Medicine, 2015) randomly assigned critically ill adults to permissive underfeeding — roughly 40 to 60 percent of their calorie targets — or to standard full enteral (tube) feeding, while giving both groups similar amounts of protein. Ninety-day mortality was similar between the two approaches, as were most other outcomes measured.

Why it matters

Intuition says that sick, catabolic patients burning through their reserves must need aggressive calories. PermiT, like several other critical-care nutrition trials, challenged that intuition: pushing to hit full calorie targets early did not improve survival, and overfeeding a critically ill patient carries its own harms, from high blood sugar to liver strain.

Analysis — the pattern

Read together with the CALORIES route trial and the early-versus-late parenteral-nutrition studies (this is analysis): a consistent pattern is that in acute critical illness, more or earlier feeding rarely beats a measured approach. Protein delivery, rather than total calories, is increasingly seen as the more important lever, though the ideal amount is itself debated. The emerging direction is personalized, phase-specific nutrition — matching intake to the stage of illness — rather than one target for everyone.

What is still uncertain

These trials studied broad ICU populations, so patients with severe pre-existing malnutrition, short bowel, or very long ICU stays may respond differently. Many clinicians separate the early, unstable phase of critical illness, when the body may not use extra calories well, from later recovery, and the best calorie and protein targets by phase remain unsettled.