# Metabolic Profiling of Type 2 Diabetes Patients after Bariatric Surgery by Raman Spectroscopy
## 4 Discussion  
Bariatric surgery (BS) is an effective method for achieving sustained weight loss and improvement in comorbidities, and as such it is an essential tool for the management of obese T2 DM patients. In this study, we examined the effects of BS on changes in the body composition and the systemic metabolism of Ob-T2 DM patients from multiple points of view. Specifically, we studied the anthropometric measurements in addition to glycemic and lipid profiles, as commonly used in clinical practice. We also measured adipokines, ghrelin, and FGF-19 levels, and studied the metabolic profile of patients using Raman spectroscopy.  
Anthropometric measurements, glycemic control, and lipid profile were taken during the baseline evaluation and follow-up visits. The reduction in anthropometric measurements after surgical treatment, in addition to improved glycemic control and lipid profile, highlighted the benefits of BS.  
Consequently, the measure of serum adipokines, ghrelin, and FGF-19 levels after bariatric procedures confirmed that patients after BS show considerable improvements and can obtain values similar to those reported in the literature [37; 38; 39; 40; 41]. However, RS data highlighted an altered metabolic profile even after BS.  
As reported in previous studies, the RS fingerprint of serum samples from T2 DM subjects is clearly different from those of HC [26; 27]. T2 DMs have lower levels of carotenoids (peaks at 1157 and 1523 cm\({}^{-1}\)) and amino acids (1408 cm\({}^{-1}\)). In addition, they show an altered profile in the secondary structure of proteins. After surgical treatment, the Raman fingerprint remains very similar to the one observed in the samples collected before the surgery, with the notable exception of the two peaks relative to carotenoids, whose intensity is even more reduced. The low level of carotenoids observed by RS is in accordance with previous work highlighting how BS induces malabsorption of vitamins and micronutrients [44; 46; 47].  
Figure 6: PCA analysis of Raman spectra. Grey dots correspond to the 23 spectra of the health control patients [HC; \(n=23\)], whereas the red and blue correspond to the 14 spectra of the obese type 2 diabetes mellitus patients [Ob-T2 DM; \(n=14\)] before and after bariatric surgery [BS; \(n=14\)], respectively.  
The fact that the metabolic fingerprint observed by RS in the BS subjects did not overlap with the Raman profile obtained from HC, despite improvements in the major clinical parameters, suggests that BS does not fully restore the metabolic profile of patients in the immediate follow-up after surgery.  
Our study has several limitations that need to be acknowledged. The first is that it includes only a small number of subjects, so our results will need to be confirmed by larger prospective studies that include more subjects. Moreover, a group containing non-obese T2 DM subjects should also be recruited in any prospective study. Another important limitation of our study concerns the relatively short duration of the follow-up period, which did not allow us to verify the continuing benefits of surgery on the glyco-metabolic profile of patients. Therefore, a follow-up at 18 and 24 months should also be included in a larger prospective study to further examine the metabolic profile of patients after surgery.