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Food-Anticipatory Rhythms under 24-Hour Schedules of Limited Access to Single Macronutrients

Department of Physiology and Biophysics, Harvard Medical School and Institute for Circadian Physiology, Boston, Massachusetts 02115

T.A. Houpt

Department of Physiology and Biophysics, Harvard Medical School and Institute for Circadian Physiology, Boston, Massachusetts 02115

M.C. Moore-Ede

Department of Physiology and Biophysics, Harvard Medical School and Institute for Circadian Physiology, Boston, Massachusetts 02115

Food-restricted rats anticipate a fixed daily mealtime by entrainment of a circadian timekeeping mechanism separate from that which generates daily light-entrainable activity rhythms. The entrainment pathways and rhythm-generating substrates for food-anticipatory rhythms are unknown. In this study, we attempted to define minimal food-related stimuli necessary or sufficient for food anticipation by employing schedules of restricted macronutrient availability, with or without free access to a complementary diet. Rats did not anticipate a daily meal of protein, carbohydrate, or fat, as measured by tilt-cage, running-wheel, or food-bin activity, when they had free access to other nutrients. However, rats did anticipate single-macronutrient meals when they were limited to only two, larger, complementary meals each day (protein-fat, protein-carbohydrate) providing a reduced total number of calories. Previous work has shown that caloric restriction per se is not a prerequisite for food anticipation. In combination with that study, the present results indicate that the size of a nutrient meal, in absolute terms or relative to total daily nutrient intake, is of pre-eminent importance in determining its value as a synchronizer of anticipatory rhythms. The results further suggest that physiological responses unique to the ingestion and absorption of any particular macronutrient are not necessary components of the entrainment pathway.

Journal of Biological Rhythms, Vol. 5, No. 1, 35-46 (1990)
DOI: 10.1177/074873049000500104


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