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¹ INSERM, U724, Faculté de Médecine, BP 184 F 54505 Vandœuvre-les-Nancy, France ² Université Henri Poincaré, EA 3453, Systèmes Neuromodulateurs des Comportements Ingestifs Nancy, 54000 Nancy, France

(Correspondence should be addressed to B Beck; Email: bernard.beck{at}nancy.inserm.fr)

In the present experiment, we examined in Long–Evans rats the long-term effects of diets that differed in the energy provided by proteins (P) and fats (F) but provided a constant level of energy from carbohydrates (55%) on various hormones regulating feeding and metabolism. Sixty adult rats were fed for 2 months either a high-fat (protein-to-fat, PF 5/40), a control (PF 15/30), low-fat (PF 30/15), or high-protein (PF 40/5) diet ad libitum. Both the PF 30/15 and the PF 40/5 rats ate significantly less than their PF 5/40 and PF 15/30 counterparts throughout the experiment (P<0.001). PF 40/5 rats weighed less than PF 15/30 rats (PL=0.04). PF 40/5 and PF 30/15 rats had smaller epididymal and perirenal adipose tissue depots than PF 5/40 and PF 15/30 rats (P<0.05 or less). Adiponectin (+25–47%) and leptin levels in the PF 5/40 rats were higher than in the three other groups (P<0.0025 or less). Ghrelin concentration in the PF 30/15 group was also higher than in the three other groups (P<0.001 versus PF 5/40; P<0.05 versus PF 15/30 and PF 40/5). Corticosterone level was 2- to 2.5-fold higher in PF 40/5 rats than in the three other groups (P<0.01 or less). Immunoreactive insulin was not different between the four groups. Our current findings thus show that increases in the protein content resulted in a greater degree of leanness, but at sufficiently high levels, also activated the hypothalamo–pituitary axis. Ghrelin appeared to be down-regulated by increases in fat content and no obvious signs of insulin resistance were observed in any of the rats under study.