Nitrogen Metabolism in Zucker Rats is Affected by Moderate Reduction, but not by Moderate Increase in Dietary Protein

Immaculada Rafecas1, Xavier Remesar2, 3, *
1 Grup Nitrogen-Obesitat, Universitat de Barcelona, Spain
2 Departament de Nutrició i Bromatologia, Facultat de Biologia, Universitat de Barcelona, Spain
3 CIBER Fisiopatología de la Obesidad y Nutrición, Instituto de Salud Carlos III, Spain

© 2012 Rafecas and Remesar.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Departament de Nutrició i Bromatologia, Facultat de Biologia, Universitat de Barcelona, Av. Diagonal 643, 08028 Barcelona, Spain; Tel. +34 934021518; Fax +34 934037064; E-mail:


Marked changes in the content of protein in the diet affects the rat’s pattern of growth, but there is not any data on the effects to moderate changes. Here we used a genetically obese rat strain (Zucker) to examine the metabolic modifications induced to moderate changes in the content of protein of diets, doubling (high-protein (HP): 30%) or halving (low-protein (LP): 8%) the content of protein of reference diet (RD: 16%).

Nitrogen, energy balances, and amino acid levels were determined in lean (L) and obese (O) animals after 30 days on each diet. Lean HP (LHP) animals showed higher energy efficiency and amino acid catabolism but maintained similar amino acid accrual rates to the lean RD (LRD) group. Conversely, the lean LP (LLP) group showed a lower growth rate, which was compensated by a relative increase in fat mass. Furthermore, these animals showed greater efficiency accruing amino acids. Obesity increased amino acid catabolism as a result of massive amino acid intake; however, obese rats maintained protein accretion rates, which, in the OHP group, implied a normalization of energy efficiency. Nonetheless, the obese OLP group showed the same protein accretion pattern as in lean animals (LLP). In the base of our data, concluded that the Zucker rats accommodate their metabolism to support moderates increases in the content of protein in the diet, but do not adjust in the same way to a 50% decrease in content of protein, as shown by an index of growth reduced, both in lean and obese rats.

Keywords: Amino acid accretion, diet, nitrogen balance, protein content, Zucker rats.