To understand the dietary influences on blood plasma metabolome of Celiac disease (CeD) patients using proton (¹H) nuclear magnetic resonance (NMR) spectroscopy and multivariate analysis methods.CeD is caused by dietary ingestion of gluten containing products which lead to villous atrophy and consequently affects the gut microflora. Diet is one of the important physiological factors which affect the metabolism of human body. Therefore, it is important to understand dietary effect on human metabolomes so that the metabolic changes due to physiological variation are not confounded with the biomarker/s of diseases. Thus, in the present study, the influence of diet on metabolic profile of blood plasma of CeD patients in comparison to controls was evaluated using NMR spectroscopy. Thirty treatment-naïve patients with CeD (mean age 25.3±10.9 years; vegetarians, n=17 and non-vegetarians, n=13) and 26 healthy controls (mean age 27.8±4.5 yrs; vegetarians, n=10 and non-vegetarians, n=16) were recruited. Vegetarian category included those subjects who have taken only vegetarian diet and they do not even take egg. While non-vegetarians were those who take non-vegetarian meals on regular basis, twice or thrice in a week. An informed consent was taken and study was approved by Institute Ethics Committee. All patients treated according to standard regimen. Diagnosis of CeD was made on the basis of European Society of Pediatric Gastroenterology Hepatology and Nutrition. Blood samples were collected in morning pre-prandial and centrifuged and plasma were separated and stored at -80 °C until NMR analysis. ¹H one-dimensional Carr-Purcell-Meiboom-Gill Sequence (CPMG) and two dimensional total correlation spectroscopy (TOCSY) NMR experiments were performed at 700 MHz (Agilent, U.S.A.). Unpaired student t-test/Wilcoxon rank sum test were used for comparison of concentration data between two groups and probability <0.05 was considered significant. Partial least squares-discriminant analysis (PLS-DA) was performed using Unscrambler 10.2 (CAMO Software, Oslo, Norway).The concentration [(μM (mean ±SD)] of metabolites was determined in patients with CeD and healthy controls are presented in Table 1. Significantly different metabolic profile was observed in CeD patients when categorized on the basis of diet (Table 1). PLS-DA showed clear distinction between CeD vegetarians and CeD non-vegetarian patients (Fig. 1); CeD vegetarians and healthy vegetarians (Fig. 2); and CeD non-vegetarians and healthy non-vegetarians (Fig. 3). The present study demonstrated the dietary induced variations on the metabolic profile of blood plasma of CeD patients. Our study revealed a significantly lower concentration of essential amino acid valine in the plasma of vegetarian as compared to non-vegetarian CeD patients. Valine is an essential amino acid and is obtained through diet. Since, non-vegetarian diet is rich in protein and fat, hence, high level of valine seen in non-vegetarian CeD patients may be related to diet¹. Further, our results showed increased level of glycine in CeD vegetarians compared to CeD non-vegetarians and this was also higher compared to healthy vegetarians. It may be noticed that alanine was significantly higher in non-vegetarian CeD compared to healthy non-vegetarian subjects. Since, glycine and alanine are both utilized in gluconeogenesis, enhanced levels of these amino acids in the blood plasma of CeD patients may probably suggest reduced gluconeogenesis in both vegetarian and non-vegetarian CeD patients. However, gluconeogenesis pathway may be more compromised in vegetarians as compared to non-vegetarian CeD patients. Further, our results showed an increased concentration of acetate in CeD (vegetarians and non-vegetarians) patients as compared to healthy subjects which may be attributed to the preference for utilization of fatty acids as energy fuel in CeD patients. Further, we observed a significantly higher concentration of pyruvate and creatine in CeD vegetarians compared to healthy vegetarians, while these differences were not seen in CeD non-vegetarians compared to healthy non-vegetarians. These findings suggested that the nutritional and energy status may be more compromised in CeD patients on vegetarian diet. The concentration of creatinine was significantly lower in both vegetarian and non-vegetarian CeD patients compared to healthy subjects which indicated malabsorption of proteins in CeD. However in this study, the metabolic profile of healthy vegetarians and non-vegetarians was similar, except that lactate was higher in healthy vegetarians. This may be due to the fact that healthy subjects included in this study belonged to the same socio-economic status, which resulted in similar nutritional status.The results suggested the influence of diet on the metabolic profile of blood plasma in CeD patients, hence, may have implications in interpretation of biomarkers for CeD diagnosis. The study showed that nutritional and energy status was comparatively compromised in vegetarian compared to non-vegetarian CeD patients while nutritional quality of vegetarian and non-vegetarian diet was similar in healthy subjects.