## 4 Discussion
Levels of total \(\omega 3\) FAs (i.e., 22:6\(\omega 3\) and 18:3\(\omega 3\)) were significantly decreased in diabetic compared to healthy animals. More specifically, 22:6\(\omega 3\) was found at similar levels in all groups, but 18:3\(\omega 3\) concentrations were lower in DCD and DPD compared to healthy ones, indicating that 18:3\(\omega 3\) levels determine the difference in the total \(\omega 3\). An elevated ratio of \(\omega 6/\omega 3\), which has been associated with insulin resistance [55; 56], was found in the DCD group compared to CD, as well as in the DPD group compared to PD, with the latter exerting a slightly better trend. VAT performs constant metabolic actions as it is implicated in the release of fatty acids into circulation [40]; therefore, its composition of fatty acids contributes to conditions such as systemic inflammation and dyslipidemia [57], rendering VAT a key organ in the disorder of T1D [23; 24]. It has been widely reported that dietary interventions are able to modulate gut microbiota and SCFA concentrations, eventually attenuating low-grade inflammation and improving glucose metabolism [58]. In this manner, fecal SCFAs and lactic acid levels were determined. Acetic acid was the predominant SCFA detected in all groups, in accordance with other studies [59]. In T1D mice, the supplementation with diets that resulted in the release of large amounts of acetate or butyrate after bacterial fermentation in the large intestine reduced plasma concentration of diabetogenic molecules, and a general attenuation of autoimmune response was recorded [60]. Lactic acid is produced by the host cells in inflammatory diseases [61], but it can also be produced by intestinal microbiota [62]. Interestingly, the fecal lactic acid concentration was significantly higher in diabetic groups at baseline compared to healthy groups. However, in the fourth week of the study, the lactic acid levels were lower in both diabetic groups and rendered to normal levels. This could probably be attributed to the injection of STZ and the induction of diabetes at the beginning of the study. On the other hand, in healthy rats, after 4 weeks of pistachio supplementation, the lactic acid concentration was increased compared to baseline values, whereas such difference was not observed in groups fed with the standard diet. Lactic acid is the major metabolic product of lactic acid bacteria, the beneficial organisms that are hosted in the GI tract [63], and as an intermediate organic acid in the bacterial fermentation of carbohydrates, it is further converted to SCFAs. It has been shown that after a prebiotic diet for 60 days, fecal lactic acid concentration was increased [64]. As previously reported [20], pistachio led to an increased presence of lactobacilli, a genus that produces lactic acid in the colon through metabolic fermentation of glucose [63]. However, lactic acid content may rise as a result of inflammation and has been suggested to cause inflammation [65]. It can be accumulated under conditions of dysbiosis, for example, in severe colitis [65], inflammatory bowel disease [37; 66] and appendicitis [67], and this can be due to the curtailment of the growth of lactate-utilizing bacteria at reduced pH conditions [68]. Further studies are needed in order to shed light on the role of lactic acid in STZ-induced diabetes. Pistachio also led to decreased levels of isovaleric acid in both healthy and diabetic rats compared to control diet-supplemented rats. In a double-blind, cross-over randomized controlled trial, fecal isovalerate was found to be decreased in volunteers that followed intervention with prebiotics, such as wheat bran extract [69]. Fecal isovalerate and isobutyrate are produced due to the fermentation of valine, leucine and isoleucine and serve as precursors for fatty acid synthesis or as nitrogen donors for the production of other amino acids [70]. These two branched-chain fatty acids are often used as biomarkers of protein catabolism, but little is known about their impact on host health [71; 72].