As I mentioned in the last entry, in 1995, Pories et al. found that Roux-en-Y gastric bypass surgery normalized blood glucose in some type II diabetics within days of the operation (1). This immediate improvement in blood glucose, which preceded any significant weight loss, led some to speculate that the blood glucose changes were a result of the effects of surgery on the gut rather than a consequence of weight loss. The gastrointestinal tract has been shown to secrete a number of hormones that can influence glucose and insulin levels and insulin sensitivity (2), and people theorized that changes in the levels of those hormones following absorptive surgery might be the mechanism by which those surgeries caused improvements in diabetes (1). Indeed, a number of papers showed that absorptive weight loss surgeries caused changes in levels of many of these gut hormones, and that these changes persisted even 20 years after the surgeries (3-5).
Other studies showed that while gastric bypass surgery altered the levels of these hormones, gastric banding surgery did not (4, 6). This makes sense, as the absorptive surgeries work by physically disconnecting some parts of the gastrointestinal tract that make the hormones, whereas the gastric banding, which is only restrictive, does not.
So, if gastric banding doesn't abate diabetes by altering gut hormone levels, how does it work? In the recent JAMA paper showing dramatic levels of diabetes remission with gastric banding, the authors found that weight loss was strongly correlated with diabetes remission, both in the gastric banding group and in the traditional diabetes therapy group (7). They conclude that "degree of weight loss, not the method, appears to be the major driver of glycemic improvement and diabetes remission in obese participants. This has important implications, as it suggests that intensive weight-loss therapy may be a more effective first step in the management of diabetes than simple lifestyle changes."
So, it seems that while gastric banding's effects on diabetes are primarily a result of its effects on weight loss, gastric bypass surgery also improves diabetes by altering levels of gut hormones that are involved in regulation of glucose and insulin. While gastric bypass surgery is generally more effective against diabetes and has a dual mechanism, the recent JAMA paper serves as evidence that with the right surgical team, gastric banding can also be very effective against diabetes in newly diagnosed patients, at least in the short term. This has generated a lot of excitement in the medical community, with some proposing gastric banding as the standard treatment for type II diabetes. However, until longer-term results have been shown, I think that assessment is a bit premature.
1. Pories WJ, Swanson MS, MacDonald KG, Long SB, Morris PG, Brown BM, Barakat HA, deRamon RA, Israel G, Dolezal JM. Who would have thought it? An operation proves to be the most effective therapy for adult-onset diabetes mellitus. Annals of Surgery 222: 339-352, 1995.
2. Drucker DJ. The role of gut hormones in glucose homeostasis. Journal of Clinical Investigations 117: 24-32, 2007.
3. Naslund E, Gryback P, Hellstrom PM, Hacobsson H, Holst JJ, Theodorsson E, Backman L. Gastrointestinal hormones and gastric emptying 20 years after jejeunoileal bypass for massive obesity. International Journal of Obesity and Related Metabolic Disorders 21: 387-392, 1997.
4. Kellum JM, Kuemmerle JF, ODorisio TM, Rayford P, Martin D, Engle K, Wolf L, Sugerman HJ. Gastrointestinal hormone responses to meals before and after gastric bypass and vertical banded gastroplasty. Annals of Surgery 211: 763-771, 1990.
5. Wilson P, Welch NT, Hinder RA, Anselmino M, Herrington MK, DeMeester TR, Adrian TE. Abnormal plasma gut hormones in pathologic duodenogastric reflux and their response to surgery. American Journal of Surgery 165: 169-177, 1993.
6. Korner J, Inabnet W, Conwell IM, Taveras C, Daud A, Olivero-Rivera L, Restuccia NL, Bessler M. Differential effects of gastric bypass and banding on circulating gut hormone and leptin levels. Obesity (Silver Spring), 14: 1553-1561, 2006.
7. Dixon JB, O'Brien PE, Playfair J, Chapman L, Schachter LM, Skinner S, Proietto J, Bailey M, Anderson M. Adjustable Gastric Banding and Conventional Therapy for Type 2 Diabetes. JAMA 299: 316-323, 2008.