Effects of Cyclic and Continuous Total Enteral Nutrition on Circadian Cortisol Rhythm

To clarify relationships between the pattern of diet intake and the circadian adrenocortical rhythm, we measured plasma cortisol levels at circadian intervals in two groups of patients who had been receiving total enteral nutrition (TEN) for about 11 days: one group was given a liquid diet intraduodenally and continuously (continuous TEN), whereas the other received their nutrition discontinuously from 0700-2300h every day (cyclic TEN). In patients with cyclic TEN there was a clear cortisol rhythm with a peak at 0700h, which pattern is quite similar to the well-established cortisol rhythm seen in normal subjects. However, patients with continuous TEN did not show any consistent circadian cortisol rhythm, although the 24-h mean cortisol level was nearly the same as that in the case of cyclic TEN. Plasma glucose levels showed circadian fluctuations in the cyclic TEN group, but remained fairly constant in the continuous TEN group. These results indicate that the periodicity of nutrient intake is essential for the maintenance of the circadian cortisol rhythm and suggest the importance of the timing of diet intake as a synchronizer (zeitgeber) of the rhythm in man, as proposed in laboratory animals.