Previous studies have shown that histological changes in the gastric mucosa between obese and non-obese individuals do exist, mainly in the cells producing the hormone ghrelin, but also in other gut hormones. Understanding these histological differences (between obese and non-obese individuals) might elucidate obesity pathophysiology, however, the data is scarce and even contradictory. Even less is known about the histological characteristics of the duodenal mucosa in obesity and lean states, but several studies already performed hint for some differences.. In conclusion, the investigators assume that obese and non-obese individuals may have gastric and/or duodenal histological differences. These differences might influence gut hormones composition and function and play a crucial role in the development of obesity and metabolic syndrome. To our best knowledge, in-vivo, human, real-time cellular level comparison of gastric and duodenal mucosa as well as differences in the microbiome of the stomach and duodenum between obese and non-obese individuals has never been done. This can be now accomplished with pCLE.