amount of PHP supply in malnourished of young rats and to evaluate the impact of nitrogen (N) supply on weight gain and nitrogen balance. Methods: In a first set of experiments, 8 young male Sprague Dawley (SD, 70 g bw) rats were fasted for 2 days and refed during 3 days with either 90%, 100% of normal caloric intake, or ad libitum (AL). In the second set of experiments, 15 young male SD rats (60 g bw) were randomised into 3 groups in order either to receive normal feeding (control group C) or to undergo a 2-day fast and ad libitum refeeding with PHP or IP for 13 days. Body weight, caloric intake and N balance were measured daily, and body composition was determined at euthanasia. Results: In the first study weight regain was 15 (p < 0.05), 8 and 1% (NS) below initial weight respectively for the 90%, 100% and AL groups. In the AL group N efficiency was 11 and 24% higher respectively than in the 90% and 100% groups (NS). In the second study weight was 19% (p < 0.05) and 9% (NS) lower for PHP and IP vs C. At similar caloric intakes (412 kcal/d) IP allowed a 62% (p < 0.05) higher recovery of N balance and a 5% increase (p < 0.05) in lean muscle mass compared to PHP. Conclusion: Our results show benefits of an ad libitum refeeding on growth with no needs to monitor and/or restrain caloric intakes. Furthermore IP improves lean muscle mass and N balance to a further extent although it does not allow reaching a complete catch-up growth after 13 days of refeeding as long as malabsorption in this model might be insufficient to highlight benefits of PHP.