Modifications of circadian cortisol rhythm by cyclic and continuous total enteral nutrition

To clarify the relationship between the pattern of diet intake and the circadian adrenocortical rhythm, we measured plasma cortisol levels at 4-h intervals over a 24-h period in 18 patients who were in the vegetative state and had been receiving total enteral nutrition (TEN) for 4 weeks. One group of 6 patients was given a liquid diet intraduodenally and continuously throughout a day (continuous TEN), whereas the two other groups received their daily enteral feeding during a restricted time of day, either in the daytime from 0800 h to 2000 h (diurnal TEN, 6 patients) or in the nighttime from 2000 h to 0800 h (nocturnal TEN, 6 patients). In patients with diurnal TEN, there was a clear cortisol rhythm with a peak of 0800 h, whose pattern was quite similar to the well-established cortisol rhythm in normal subjects. Patients with nocturnal TEN also showed a cortisol rhythm, but the peak appeared at 1600 h. There was no appreciable difference in the amplitude of the rhythm between the two groups. Patients with continuous TEN did not show any consistent circadian cortisol rhythms. Plasma levels of glucose, insulin, and free fatty acids also showed circadian fluctuations corresponding to the pattern of diet infusion in the groups with diurnal and nocturnal TEN, and remained almost constant throughout a day in the group with continuous TEN. We conclude from these results that the timing of diet intake may have a synchronizing effect on the circadian cortisol rhythm in man, as it does in laboratory animals.