Franny Jongbloed

91 4 A PROTEIN-FREE DIET PROTECTS AGAINST RENAL IRI Compared to the corresponding control group, three days of fasting showed a significant two-fold increase in relative ribosomal protein S6 phosphorylation (Figure 4). In the other dietary interventions, a large variation in phosphorylation levels was observed which did not reach statistical significance. DISCUSSION Since the discovery of the beneficial effects of short-term dietary restriction (DR) on stress resistance, optimizing its duration and content to eventually lead to a clinical applicable DR regimen has been an important part of the body of literature about DR 2,11,19 . Previously we have shown that two and four weeks of 30% DR as well as three days of fasting decreased morbidity and mortality, and improved kidney function in a murine renal IRI model 1,12 . In the present study, we show that a protein-free diet administered for only three days is sufficient to induce similar protection, whereas fat- and carbohydrate-free diets did not. Initially, we attempted longer periods of diet interventions, but found that mice fed a protein-free diet during 10 days applied self-restriction of approximately 30% of their normal intake (Figure S1). Therefore, the possible beneficial effects of calorie and protein restriction on kidney function and survival were indistinguishable. In a recent publication, Peng et al. found that mice fed a protein-free diet for six days restricted calorie intake. However, they stated that corrected for body weight, their calorie intake was similar to that of ad libitum fed mice 19 . It is unknown whether six days of 30% DR induces protection against IRI, therefore a distinction between protein restriction and calorie restriction is still difficult to make. We showed that three days of 30% DR does not induce protection against renal IRI, and therefore we could disentangle the effects of calorie and protein restriction per se (Figure 1). A protein-free diet, given for three days induced protection, whereas both a CHO-free and fat-free diet given for three or 14 days did not protect against renal IRI (Figure S1). A recent publication by Solon-Biet et al 26 showed that the ratio of proteins and carbohydrates rather than DR per se influenced the lifespan of mice as well as metabolic parameters such as insulin and lipids. Since proteins fully substituted the carbohydrates in our CHO-free diet, and carbohydrates fully substituted the proteins in our protein- free diet, these diets further emphasize the importance of the ratio between proteins and carbohydrates (Table S4).