An emerging concept in clinical nutrition is that dietary interventions may improve the course of systemic inflammatory disorders like rheumatoid arthritis and psoriasis. Most of this effect depends on the ability of polyunsaturated fatty acids (PUFAs) to modulate immune and inflammatory responses. Two main families of PUFAs exist in human tissues: n-3 PUFAs that have a marked anti-inflammatory activity and n-6 PUFAs that, conversely, promote inflammation. Multiple mechanisms account for the modulation of the inflammatory response by PUFAs. Recent lipidemic studies have added new mediators like lipoxins to the list of PUFA metabolites controlling inflammation that classically included only pro-inflammatory or anti-inflammatory prostaglandins like PGE2 and PGE3, respectively. The concerted activity of these mediators may determine a decreased recruitment of inflammatory cells in target tissues, with a lower release of pro-inflammatory cytokines like Interleukin-6 (IL-6) and necrosis tumor factor-α (TNF), and their higher apoptosis rate.

n-3 PUFAs include α-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), whereas linoleic acid (LA) and arachidonic acid (AA) are the main n-6 PUFAs. ALA and LA are both essential fatty acids because they cannot be synthetized in the human body and have to be assumed with the diet. They are the precursors of downstream immunomodulatory long-chain fatty acids: LA is converted to AA that has marked a pro-inflammatory activity and is further transformed in pro-inflammatory eicosanoids (PGE2) and leukotrienes. On the contrary, ALA is converted to EPA and DHA, the precursors of anti-inflammatory prostaglandins (PGE3) and inhibits the production of AA and the synthesis of thromboxane. Importantly, the amount of ALA converted to EPA and DHA in humans is usually low which makes also these fatty acids essential. The current western diet is poor of n-3 PUFAs and this suggests that n-3 PUFAs-dependent endogenous anti-inflammatory mechanisms could be potentiated by simultaneously increasing n-3 PUFA intake and lowering the n-6/n-3 ratio. Indeed, a high n-6/n-3 ratio is associated to a worse clinical course in cardiovascular, inflammatory and autoimmune diseases. With the rationale of increasing n-3 PUFAs intake and of lowering the n-6/n-3 ratio, n-3 PUFAs supplementations like fish oil have been given with favorable clinical results to patients affected by different chronic inflammatory diseases including rheumatoid arthritis, inflammatory bowel disease, and psoriasis. Fish oil, however, has a low palatability and this may cause a low patients' compliance during prolonged therapy. Since seafood, and several fruits and vegetables have a high content of n-3 PUFAs, dietary regimens based on these specific foods are expected to increase n-3 PUFAs intake., thus representing an attractive alternative to the administration of exogenous fish oils products in therapeutic programs aimed to exploit the beneficial n-3 PUFAs effects in systemic inflammatory disorders.

Therefore, the investigators explored the effect of a diet based on food with a high n-3 and low n-6 PUFAs content in long-term kidney transplant recipients. These patients could benefit from an increase in n-3 PUFAs intake because a persistent systemic inflammatory status occurs after kidney transplantation, that greatly contributes to the development of cardiovascular diseases and of chronic allograft dysfunction. Previous studies showed that dietary administration of n-3 increases graft survival in different animal models of organ transplantation, whereas n-6 PUFAs had opposite effects. Recently, the efficacy of n-3 PUFAs supplementation with canola oil in decreasing systemic inflammation and in lowering the incidence of rejections was demonstrated also in humans.