**2.5 Non-alcoholic fatty liver disease (NAFLD)**

NAFLD is liver steatosis in the absence of secondary causes of hepatic fat accumulation such as alcohol abuse. NAFLD can progress to nonalcoholic steatohepatitis (NASH), liver cirrhosis, liver failure, and hepatocellular carcinoma [22]. It is linked to obesity and frequently associated with metabolic syndrome [22]. WL and metabolic improvement post LSG result in a significant improvement in NAFLD. In one study, a liver biopsy was obtained in 134 LSG patients during surgery and 192 days after surgery [23]. There was significant improvement in liver histology following LSG, evident by the improvement in NALFD-Activity-Score (NAS) (P<0.001) [23]. NAS is a scoring system developed as a tool to measure changes in NAFLD during therapeutic trials [24]. In the previous study, the percentage of patients with NASH decreased from 18% to 3% [23]. The improvement was greater in severe cases of NAFLD including those with steatohepatitis, bridging fibrosis or cirrhosis. LSG does not only improve the histology and liver function of patients with NAFLD but also reduces the oxidative stress and inflammatory processes involve in the mechanism of NAFLD, where there was significant changes in plasma and liver markers of oxidative stress and inflammation (including chemokine C-C motif ligand 2, paraoxonase-1, galectin-3, and sonic hedgehog) [25]. These data suggest that LSG could be used as therapeutic option to improve NAFLD.

#### **2.6 Obstructive sleep apnea (OSA)**

Severe obesity is associated with a high prevalence of moderate-to-severe OSA. A metanalysis showed that at a mean of 24.7 months, LSG resulted in

resolution and improvement of sleep apnea in 72% and 51% of patients respectively [26]. One study showed that the apnea hypopnea index significantly decreased from 45.8 to 11.3 events/hour ten months post LSG [27]. The rapid improvement of moderate-to-severe OSA observed post LSG is likely due to the reduced neck circumference. Interestingly, this does not correlate with EWL% which suggests that a weight-independent factors may play a role and hence warrant further research [27].
