Gastric Bypass and Ghrelin

Recently the medical community has had a difficult time identifying the role that ghrelin, a hormone released from the stomach and hypothalamus, has in weight loss following bariatic surgery. Ghrelin has been shown to be a potent appetite stimulator and may play a role in weight regulation following bariatic surgery. The goal of the experiment was to address the discrepancies arising from conflicting experimental evidence on whether or not plasma ghrelin levels play a role in weight regulation following significant weight loss after laparoscopic Roux-en-Y gastric bypass (LRYGBP). Furthermore, the researchers took into consideration two other hormones: insulin and adiponectin, which have been shown to help regulate ghrelin levels in the body. The article sites evidence indicating that obese individuals have low adiponectin plasma levels (24-26), and that low adiponectin levels have been shown to cause insulin resistance (27). Hyperinsulinemia which is indicative of obesity may be the primary factor in the low ghrelin levels seen in these individuals (28-29). By addressing insulin and adiponectin levels along with plasma ghrelin levels, the researchers look to develop a more comprehensive understanding of how or if plasma ghrelin levels effect the weight loss of obese individuals following a LRYGBP.

The researchers used a sample of 49 morbidly obese subjects who underwent LRYGBP for the treatment of morbid obesity. A control group was also used consisting of 19 subjects who underwent other types of laparoscopic surgeries by the same surgeons. Blood was taken from both groups at 1 hour preoperatively, and then at 2 hours, 10 days, and 6 months postoperatively. By taking blood samples at intervals ranging from hours to months, the researchers aimed to identify the fluctuations in hormone levels at times that corresponded to specific stages of weight loss following the surgery. For example, by taking hormone levels 2 hours postoperatively the researchers could record the immediate effects that the LRYGBP had on hormone levels. After 10 days the researchers recorded the hormone levels at a time postoperatively but also prior to any significant homeostatic changes occurring in response to reduced food intake and severe weight loss. And finally the hormone levels were measured at a point when weight loss had occurred and the subjects’ body had enough time to reach a new homeostatic equilibrium. Hormonal assays were used to determine the plasma levels for ghrelin, insulin, and adiponectin. Preoperatively, the ghrelin levels where lower in the experimental group compared to the control group. The lower ghrelin levels could have been attributed to the higher body mass index (BMI) of the experimental group. The higher BMI in the experimental group indicated that comparatively the experimental group was more obese than the control group. However, if the experimental group was more obese, they would have had a more severe condition of insulin resistance, which would mean higher insulin plasma levels. This would have lead to lower ghrelin levels due to insulin’s ability to inhibit ghrelin production. At two hours postoperatively a statistically significant drop in plasma ghrelin levels in both the experimental and control groups was observed. Then, 10 days postoperatively the ghrelin levels continued to be reduced in the experimental group but normalized in the control group. Later, at six months post operation the ghrelin levels in both groups had normalized to near preoperative levels. This happened despite considerable weight loss experienced by both groups. With ghrelin levels near preoperative levels at 6 months after surgery it is important to note that the ghrelin levels had not changed even though weight was lost. The insulin levels in the experimental group were significantly higher than the control group's prior to the surgery. Six months post-surgery however, the experimental group showed a significant reduction in insulin levels, indicating a reduction in insulin resistance in subjects of the experimental group. Adiponectin levels were similar in both the control and experimental groups prior to surgery. Two hours after surgery the levels dropped in both groups, but at the 10 day mark, levels were back to the preoperative levels for the control and experimental groups. Six months later however, the researchers recorded a significant rise in the plasma adiponectin levels in the experimental group.

The results of the experiment indicate weight loss after LRYGBP is independent