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Looking for answers to bariatric surgery for losing weight using resting state functional MRI

Obesity is a worldwide public health epidemic. Research demonstrates that obesity is associated with an increased risk of developing many physical conditions including diabetes and high blood cholesterol (Ogden et al., 2014). Bariatric surgery is one efficient therapy to losing weight. Previous functional MRI (fMRI) studies have found that obese patients undergoing surgery demonstrate aberrant neural activity and resting state functional connectivity (Frank et al., 2014; Lepping et al., 2015). However, no previous studies have tested the difference in resting state neural activity before and after bariatric surgery. In this issue of EJN, Wiemerslage et al. assessed the interactive effect of bariatric surgery and prandial state using resting state fMRI (Wiemerslage et al., 2016). They found altered neural activity in the putamen and insular cortex, core regions in self-referential processing within eating behaviors (Esposito et al., 2016). Their findings extend previous work to provide further evidence that resting state neural functions are rapidly affected following surgery and weight loss. Furthermore, the current study provides novel insight into understanding the mechanisms by which bariatric surgery alters psychological functioning, the surgery alters feelings of hunger/satiety base on affecting selfreferential processing and learning. This study raises several questions for future study. Although the current study showed altered neural activity following surgery, the investigators did not investigate the relationship between resting state brain activity and physical measurements. Previous study showed ariatric surgery could modulate the secretion of many gastrointestinal hormones (le Roux et al., 2007), and hormones could mediate the brain activity (Zhang et al., 2015). Secondly, Wiemerslage and colleagues used a small sample size and assessed only female subjects. The reliability and generalizability of this study would be greater had the authors included a larger cohort representing both sexes. Indeed, previous studies have shown gender differences in brain activation in response to food intake (Del Parigi et al., 2002). In the current study, MRI scans were collected in the morning after subjects fasted for more than 12 h. Future studies should enlarge the sample size and assess the effect of the time of MRI-scan acquisition (morning, afternoon, evening) and the length of fasting on neural variability. Furthermore, in the current study, all subjects adopted a low-calorie diet in preparation for surgery and a new healthier lifestyle after Wiemerslage et al.’s initial assessments. This potentially confounding variable could also, at least partially, explain changes in neural activity reported in the study. Previous research has found opposite resting state functional connectivity patterns between behavioral dieters and bariatric patients. Behavioral dieters exhibited increased connectivity between left precuneus and bilateral insula preto post-meal and bariatric patients exhibited decreased connectivity between these regions (Lepping et al., 2015). Last, the study showed that the mean post-prandial hunger ratings decreased 43% and mean fullness ratings increased 47% as a result of bariatric surgery. The main reason for the decrease in hunger ratings may that the stomach volume of each subjects reduced as a result of surgery, but the volume of the liquid food unchanged, 250 mL of a milk-based drink. The primary force driving the increase in satiety are the kinds and amounts of food subjects consumed. For scientific research, the amount of food consumed should be standardized by each subject. However, it remains unclear how the optimal caloric intake for each subject should be determined. Researchers may administer an amount proportional to each subject’s body size or a fixed amount. Though one study found no differences in the regional cerebral blood flow in response to a meal were found between two kinds of amount (Le et al., 2006), future studies would investigate such problem more and find out the optimal caloric intake. Overall, the study of Wiemerslage et al. provides novel insights into bariatric surgery for weight loss, and also provides a useful paradigm into developing other strategies for losing weight using resting state fMRI.