Circadian pitfalls in experimental designs employing food restriction

Abstract

Most physiological and behavioral processes exhibit prominent circadian (24-h) rhythms that maintain a stable phase relation to daily light-dark cycles by means of entrainment. These rhythms can introduce interpretative confounds in experimental paradigms if lighting schedules and circadian phase of testing are not sufficiently controlled. The present review seeks to highlight another potential circadian confound implicit in experimental designs that utilize food-restriction schedules: Such feeding schedules markedly alter the timing of most daily rhythms of behavior and physiology. Evidence is reviewed that this reflects entrainment of a distinct food-entrainable circadian oscillator analogous to the light-entrainable circadian oscillator that has been localized within the hypothalamic suprachiasmatic nuclei. Entrainment of this oscillator may occur under any experimental condition in which food is ingested at a relatively fixed time of day. Lack of awareness of this entrainment process and how it may vary with the parameters of the feeding schedule can have serious ramifications, ranging from increased variance in dependent measures to the generation of spurious results and interpretations. © 1990, Psychonomic Society, Inc.. All rights reserved.