The relative success of bariatric surgery, when measured in terms of weight loss, varies with procedure, with LABG resulting in the least weight lost and BPD/DS the most [4
]. However, substantial heterogeneity in weight loss success is seen amongst patients having the same procedure. The factors responsible for variation in weight loss success are dependent on a multitude of factors, including psychological issues, dietary factors, psychosocial circumstances, and medical comorbidities [5
]. It is postulated that hormonal differences may play a role in the variations seen in weight loss success as well.
There is currently no consistently accepted definition for weight loss failure after bariatric surgery. An excess weight loss of <50% has been considered to represent failure [68
], whereas other studies have defined surgical failure as a failure to achieve a BMI of <40
]. Heterogeneity in the reporting of absolute percent weight loss versus percent of excess weight lost (EWL) between studies creates further difficulty in navigating this literature.
In general, the nadir weight loss seen following bariatric surgery is at approximately 12–16 months, with a small amount of weight regain following [1
]. However, there is great variation in weight trajectory amongst individuals having the same procedure performed, with some patients able to sustain most of the weight loss, and others regaining much of the weight that was initially lost. Whether or not a patient experiences weight recidivism is also very likely multifactorial, with mental health issues, dietary issues, and hormonal factors postulated to be contributory [5
The very limited data currently available regarding the potential association of hormonal variations with weight loss failure or recidivism in the bariatric surgery population are summarized by procedure below.
4.1. Laparoscopic Adjustable Gastric Banding
Few studies have examined whether there is a relationship with LAGB induced weight loss success and hormonal changes. The current balance of the literature does not point to any hormonal mediators or predictors of weight loss success or failure with LAGB.
One study examined preoperative ghrelin levels and found that women with higher ghrelin levels prior to LAGB had similar weight loss results 2 years postoperatively, compared to women with lower preoperative ghrelin [70
]; thus, preoperative ghrelin levels do not appear to be a predictor of successful weight loss induced by LAGB. Another study, which found an increased area under the curve (AUC) for ghrelin release in response to a meal challenge at 1
y after LAGB, found no correlation between ghrelin levels (fasting or AUC) and degree of weight loss [36
]. Leptin decrease at 1
y after LAGB has been found to correlate with the degree of weight loss after LAGB. As this is seen with dietary induced weight loss as well, it is thought to be an effect of weight loss and not causative [36
We are not aware of any literature regarding hormonal associations with weight recidivism following LAGB.
4.2. Sleeve Gastrectomy
As the SG is a newer procedure which has only recently been recognized as a standard option for bariatric surgery [71
], there is little long term data available on the efficacy of SG and even less in regard to hormonal variations that may play a role in weight loss failure or recidivism.
One study followed 26 SG patients through 5 years and found that %EWL was 55% at 5 years, with 19% of patients regaining >10
kg from their nadir weight loss [43
]. Amongst those patients who regained weight, a slightly higher plasma ghrelin was seen; this did not reach statistical significance, which may have been due to the small sample size. A rodent study showed that serum bile acids correlated positively with weight loss success following SG [23
4.3. Roux-en-Y Gastric Bypass
PYY appears to play a role in the degree of weight loss obtained following RYGB. One study found that patients in the highest quartile of %EWL at 6 weeks post-op had a higher postprandial PYY response compared to those in the lowest quartile [72
] and that a higher PYY response at 6 and 52 weeks post-op predicted a larger %EWL at 33 months postoperatively. Further, the patients in the highest %EWL quartile had a slightly higher PYY response at 33 months compared to their own PYY response at 12 months, whereas the PYY response in the patients in the lowest quartile of %EWL had not changed from 12 months to 33 months post-op. This study also found that lower ghrelin levels at 6 weeks post-op were associated with a larger weight loss at 33 months, but this association became nonsignificant when PYY was taken into account. Thus, it appears that the prandial PYY response shortly after surgery may be a predictor of more successful long term weight loss following RYGB.
The postoperative GLP-1 response to a meal appears also to play a role in successful weight loss following RYGB. A small study found that patients with the least amount of weight loss at approximately 2 years after RYGB had smaller prandial PYY and GLP-1 responses compared to the patients in the cohort with the best weight loss success [73
A study which did not find any significant changes in levels of ghrelin in the fasting state or in response to a meal challenge at 1 year following RYGB also found no correlation between degree of weight loss and ghrelin levels [36
]. However, in a rodent model, postoperative weight loss was correlated with the magnitude of decrease in ghrelin levels [74
]. Similar to weight loss induced by lifestyle alterations, the degree of leptin decrease at 1
y after RYGB has been found to correlate with the degree of weight loss [36
Interestingly, the cardiac hormone B-type natriuretic peptide appears to be increased following gastric bypass surgery and correlates directly with the degree of weight loss [75
]. That BNP has been shown to induce lipolysis as well as slow gastric emptying, and absorption suggests that BNP may have an etiologic role in successful weight loss [76
]. Amino-terminal pro-B-type natriuretic peptide (NT-proBNP), a byproduct of BNP production, has been shown to be positively correlated with adiponectin, though the nature of this relationship has not been established [76
Approximately 20% of the patients regain substantial weight within 1–3 years following RYGB [77
]; the mechanisms by which this occurs are poorly understood. It has been suggested that patients who experience weight regain may manifest a particularly powerful neuroendocrine-metabolic starvation response to their initial weight loss that favors metabolic energy conservation and weight regain [78
]. In a rat model of RYGB, rats who regained weight were found not to have the severalfold increase in plasma PYY concentration that was evident in rats that had sustained weight loss success [79
]. In another rodent study, plasma leptin levels decreased less in the rats who regained weight compared with those who had sustained weight loss; it was postulated that the ratio of PYY to leptin may be of greatest importance, with a lower ratio associated with failure to maintain weight loss [78