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Dietary Effects on Body Weight, Feed Intake and Diurnal Feeding Behavior of Genetically Obese Rats^1,2,3,

Dairy and Animal Science Department, The Pennsylvania State University, University Park, Pennsylvania 16802

Diurnal feeding behavior was studied in young lean and obese Zucker rats fed diets containing equal digestible energy per g in which 60% of the energy was supplied by protein, carbohydrate or fat ad libitum. Food intake of both rat types fed the protein (PRO) diet was less than intake of rats fed carbohydrate (CHO) or fat (FAT) diets. Obese rats consumed more food during both the 12-hour light period and the 12-hour dark period than lean rats. Compared to intake of CHO or FAT diets, intake of obese rats fed the PRO diet was depressed to a greater extent than for lean rats. Further, intake of obese rats fed the PRO diet showed no temporal adaptation while intake of PRO diet by lean rats increased slightly. Eating duration was greatest and estimated eating rate slowest for rats fed the PRO diet. Obese rats displayed a tendency to equalize food consumption over a 24-hour period. A higher proportion of daily intake was consumed during the light period (40.8%) by obese rats compared to lean rats (32.4%). Estimated eating rates of obese rats fed CHO or FAT diets were slower than for lean rats. Obese rats also had similar estimated eating rates during the dark period and light period whereas lean rats exhibited a faster dark period estimated eating rate than during the light period. In summary, the studies have indicated that diurnal patterns of feeding behavior were quite different in lean and obese Zucker rats fed diets varying in source of energy.

KEY WORDS: • obese rats • diurnal feeding • hyperphagia

¹ Authorized for publication as paper no. 4981 in the journal series of the Pennsylvania Agricultural Experiment Station.

² Supported in part by NIH BSSG 5505RR 07082-08 to PJW and NIH Grant HD 07090-03 to RJM.

³ From thesis submitted by B. Dilettuso in partial fulfillment of the requirements for the M.S. degree.

⁴ To whom reprint requests should be sent.

Manuscript received 25 June 1976.