/ eh11 5057 Mp 617 Thursday Jul 10 01:31 AM EL–PB (v. 62, no. 3) 5057 617 Physiology & Behavior, Vol. 62, No. 3, pp. 617–622, 1997 Copyright  1997 Elsevier Science Inc. Printed in the USA. All rights reserved 0031-9384/97 $17.00 / .00 PII S0031-9384( 97 ) 00176-5 Differential Gender Response Produced by Meal and Ad Lib Feedings of a High-Fat Diet in Osborne – Mendel Rats VIRGINIA E. UHLEY, SHAOBIN ZHONG, FENG GUO, ANNE BUISON, LINDA SAVONA, AHMEENA WATKINS AND K-L. CATHERINE JEN 1 Department of Nutrition and Food Science, 3009 Science Hall, Wayne State University, Detroit, MI 48202 USA Received 24 July 1995; Accepted 11 March 1997 UHLEY, V. E., S. ZHONG, F. GUO, A. BUISON, L. SAVONA, A. WATKINS AND K-L. C. JEN. Differential gender response produced by meal and ad lib feedings of a high-fat diet in Osborne–Mendel rats. PHYSIOL BEHAV 62 (3) 617–622, 1997.— We investigated if there were gender differences in metabolic consequences produced by meal feeding of a high-fat (HF) diet in male and female Osborne–Mendel rats. An HF diet was fed either ad lib (AL) or in 1 meal (MF) during the last 3 h of the dark cycle for 4 weeks (lights off from 2400 h to 1200 h). All rats were sacrificed at 1 of 3 time-points: prior to MF rats receiving their food at 0900 h, after food was taken from MF groups at 1200 h or 1500 h. Food intake, body weight, body fat weight, retroperitoneal adipose tissue lipoprotein lipase activity, plasma cholesterol, or HDL-cholesterol levels did not differ between MF- and AL-fed groups, but were higher in male than in female rats. There were no differences between the male and female groups in plasma levels of insulin and glucose or systolic blood pressures. Plasma triglyceride levels at 1200 h were significantly different between MF and AL Groups within either gender, but this was not observed at 0900 h or 1500 h. Body weights were correlated with internal fat weights and plasma cholesterol levels in both males ( r Å 0.57, p õ 0.05) and females ( r Å 0.59, p õ 0.05). Hence, it is the amount of HF diet ingested, rather than the pattern of meal feeding, that was the most significant factor related to gender differences in weight gain, increases in fat mass, and metabolic differences.  1997 Elsevier Science Inc. Gender differences Meal-feeding High-fat diet Adipose tissue lipoprotein lipase Weight gain 1 To whom requests for reprints should be addressed. E-mail: CJen@lifesci.wayne.edu THE frequency of meals and diet composition have both been suggested to influence the regulation of energy balance in hu- mans and animals (1,6,16,27,34,36). Several studies have ex- amined these influences in relation to weight loss, weight gain, and weight maintenance (10,34,36). The accumulation of vis- ceral body fat and elevations in blood substrate levels have been shown to be enhanced in animals and humans when food intake is limited to only a few h per day (3,10,19,24,39). However, study of the deposition of fat in the visceral and SC depots in relation to the intake of high-fat diets and meal frequency have produced different results ( 9 ) . Differences in the duration of ex- posure to food and feeding frequency reported in these studies may well explain some of these conflicting reports. Meal-fed an- imals restricted to 1 or 2 feedings per day have been reported to have a lower total energy intake than ad lib fed animals or those fed many small meals throughout the day (3,19,36,39). These differences in energy intakes have made comparisons between meal feeding patterns and their influence on weight gain and on adipose tissue mass difficult to interpret. In addition, the strain, gender, and age of the rats studied have all been shown to influ- ence the degree to which diet affects weight gain and increases in adipose tissue mass (17,18,22,28,30). Therefore, all of these parameters need to be investigated to elucidate the influence of meal-feeding patterns on energy balance. The accumulation of body fat is enhanced in response to the ingestion of a diet high in fat (12,18,26). However, the activity of enzymes involved in de novo lipogenesis in adipose tissue have been shown to decline with HF feedings (3). Therefore, other mechanisms must be re- sponsible for the increased fat deposition that occurs in response to a high-fat diet. One possible metabolic parameter that may be influenced by the frequency of meal feedings and the ingestion of a high-fat diet is the activity of adipose tissue lipoprotein lipase ( ATLPL ) , the major enzyme responsible for the uptake and stor- age of triglyceride in adipose tissue (8). Elevations of ATLPL activity are well established in obesity, in weight-reduced hu- mans and rats, and in food-restricted/re-fed rats (8,14,20,23). However, the ingestion of an HF diet has been shown to produce varied responses in ATLPL activities; an increase, decrease, or no change at all have been reported (8). Differences in gender and in the location of adipose tissue depots examined may ex- plain some of these inconsistent results (14,21,31,38). It is well established that, in humans, men have higher absolute and rela- tive (to body weight) levels of visceral fat than women (21). However, females with higher waist-to-hip ratios have also been