Postprandial sleepiness: objective documentation via polysomnography

Fifteen normal volunteers were evaluated to assess the effect of a meal on sleep onset latency. The meal was administered in a counterbalanced design on 1 of 2 successive days. Subjects napped 20 min subsequent to the meal (or at the corresponding time on the no-meal day) and 1 h after the initiation of the first nap. Ten subjects completed the Stanford Sleepiness Scale (SSS) on arriving at the laboratory, and just prior to nap 1 and nap 2. Sleep onset latency after the meal was not significantly different from that obtained under the no-meal condition, but was significantly less on nap 1 as compared with nap 2 irrespective of day or meal. SSS did not reveal subjective differences in sleepiness between the initial estimate and the postmeal estimate. Only five subjects showed a decrease in sleep onset latency postprandially (1-11 min). Although group differences in postprandial sleepiness were not documented, the phenomenon was clearly exhibited by certain individuals. Thus, postprandial sleepiness is not an invariable consequence of meal ingestion; rather, it appears to be affected by numerous variables such as hunger, volume of the meal, and meal constituents.