The effect of desynchronization on meal patterns of humans living in time isolation.

We analyzed the timing of meals in nine subjects who lived for several weeks in a time isolation environment and whose free-running sleep-wake cycles lengthened markedly and lost synchrony with the body temperature rhythm for part of the study. The long sleep-wake periods (SWP) in free-running desynchrony (mean = 34 +/- 3 hours) as compared to free-running synchrony (25 +/- 1 hours) enabled us to compare meal timing in two distinct temporal frameworks and to relate them to the two major oscillators presumed to underlie circadian rhythms in man. We found that when the SWP lengthened in desynchrony, the intermeal interval (IMI) increased significantly. In half the subjects, the increase in IMI was approximately proportional to the increase in the SWP--the IMI "stretched" along with the SWP. Analysis of prelunch and postlunch IMIs indicated that the lengthening of the IMI during desynchrony was comparable in early and later parts of the subjective day. The increase in meal spacing was not due to increased caloric content of meals. The findings support an interpretation of dual regulation of meal timing. Proportional increases in IMI and SWP suggest that the mechanism governing the timing of the sleep-wake cycle also governs meal timing. The less than proportional increase in some cases suggests that an additional, probably metabolic, mechanism tends to limit the intervals between meals.