Exploring the long-term prevalence of weight regain in a large sample of Dutch patients who had undergone RYGB or SG, the present study found that the prevalence differs greatly depending on which of six different definitions is used, with weight regain rates ranging from 16 to 87%. In addition, the factors related to weight regain differed for each of these definitions. A higher preoperative BMI and a younger age at the time of bariatric surgery were related to a greater likelihood of experiencing weight regain in three definitions. SG surgery was related to a greater likelihood of experiencing weight regain in one of the six definitions. Three definitions of weight regain were related to deterioration in HRQoL according to the PHS of the RAND-36. Associations with the presence of comorbidities at 5-year follow-up were weak.
As expected, the definition of weight regain greatly influenced weight regain prevalence. Interestingly, the prevalence (16–87%) was considerably lower than in previous studies. The study by Lauti et al. found a prevalence ranging from 40 to 91% according to the same definitions as the present study . The study by King et al. included 1286 of 1406 patients in the weight regain sample, meaning 91% of patients had regained weight. Of this 91%, 44–62% experienced significant weight regain according to the definitions that were also used in the present study . In the present study, percentages were considerably lower, at 21–37%. This might be partly explained by the lower preoperative BMI in the present sample compared to the sample of Lauti et al., as higher preoperative BMI is associated with a greater likelihood of weight regain. However, in the study by King et al., preoperative BMI was comparable to the present study [8, 10].
Another explanation might be that the treatment program of the NOK is different to the “general” bariatric surgery center. In line with recommendations, patients at the NOK follow an intensive multidisciplinary treatment program before and after surgery focusing on changing dietary and physical activity behavior [23, 27, 28]. Research has shown that long-term multidisciplinary support is important for maintaining positive changes after bariatric surgery and may play a role in preventing weight regain [29, 30]. Another study showed similar weight loss trajectories to the present study . Unfortunately, it is difficult to compare this study to others because of the different definitions used, as well as different, or variable, follow-up periods [4, 5]. This emphasizes the need for consensus and standardized outcome reporting of weight regain.
The results confirm that some weight regain occurs in the vast majority of patients who undergo bariatric surgery, with 87% of the total population experiencing “any weight regain,” which is in agreement with several other studies [6,7,8, 12, 31]. These results suggest that some regain is normal, rather than clinically significant.
Preoperative BMI was positively related to weight regain when definitions were based on changes in BMI, %EWL, and kilograms. Recent studies have also shown that weight loss measures based on %EWL or BMI are influenced by preoperative BMI, and this study confirms that these measures are less suitable for comparing patients [32,33,34,35].
Interestingly, age was inversely related to weight regain, which has been described previously . One possible explanation is that younger patients represent a high-risk group, in which problems related to weight gain are more severe. Future research into weight regain risk at a younger age and targeting regain with additional interventions is needed.
Since HRQoL is considered to be one of the key outcomes of bariatric surgery, clinically significant weight regain should be associated with deterioration of HRQoL . Three definitions of weight regain (regain > 10 kg, regain 5 BMI, and regain EWL 25) were related to the physical health component of the RAND-36, measuring HRQoL. Several studies have shown that HRQoL improves after bariatric surgery and that this improvement is related to the amount of weight lost [3, 37,38,39]. They also show stronger associations with the physical health component than the mental health component [38, 40]. Contrary to expectations, the negative association of weight regain with HRQoL was not significant in the > 15%TWR definition. This may be due to the fact that the RAND-36 is a generic HRQoL questionnaire, which might not be sufficiently sensitive to capture changes in HRQoL as a result of bariatric surgery . Therefore, the percentage of 15% might be too small to be clinically significant.
The other key outcomes related to weight regain data were comorbidities at 5-year follow-up. These associations were weak for all definitions of weight regain. Only weight regain > 10 kg and weight regain to a BMI > 35 were significantly related to one comorbidity—that of OSA. These results suggest that none of the six definitions is suitable to predict key clinical outcomes with respect to comorbidities.
In one of the previous studies, a continuous measure that was quantified as a percentage of maximum weight lost performed best on association with clinical outcomes . This is in line with the fact that measures based on kilograms, BMI, or %EWL are not suitable to compare patients with different BMI [32, 34]. A measure reflecting a percentage of total weight loss or regain would, therefore, be more suitable, especially since percentage of total weight loss is now the measurement of choice when reporting weight loss after bariatric surgery .
One can argue whether there is a need for a definition of significant weight regain if there is a solid definition of surgical success. Van de Laar et al., for example, suggested that a definition of weight regain would be unnecessary if a cutoff curve for weight loss success was used . Weight regain from that perspective is only relevant if it exceeds the point where surgery is no longer considered a success. However, not differentiating between insufficient weight loss and weight regain ignores the possibly different mechanisms causing weight regain or weight loss failure. Patients experiencing weight regain may benefit from different interventions than patients who experience insufficient weight loss.
All current definitions of weight regain and successful weight loss only use a measure of body weight to define success, ignoring health status and patient experience of weight loss failure or relapse [4, 5, 8]. Ideally, other key outcomes after bariatric surgery, such as improvement or remission of comorbidities and improvement of HRQoL, should also be included when defining whether weight regain is significant . Developing such a clinically relevant definition that takes all important dimensions into account is challenging and, therefore, it should not only involve scientific and clinical experts but also patients, with the aim of reaching worldwide consensus.
The most significant limitation of this study is that the loss to follow-up percentage at 5 years after surgery was 70%. With the inclusion of patients who filled in an online questionnaire, this was still 65%. This is a known problem in most studies of bariatric surgery, with mean compliance at long-term follow-up low . As a result, this study relied, in part, on self-report measures for patients who were recruited to complete an online questionnaire. Differences between patients included in the NOK database and the patients who completed the online questionnaire were small. The status of comorbidities was determined by a medical doctor based on patient-reported medication use and blood pressure. Because HBA1c and cholesterol measures were not available, smaller differences in the status of a comorbidity may have been overlooked. As a result, associations between weight regain and comorbidities may have been more difficult to establish. Another limitation is that the proportion of patients who underwent SG was relatively small. Despite the loss to follow-up, this study still involved a large sample. It is the first study to apply different weight regain definitions to such a large sample of patients who have undergone RYGB or SG and thus provides comprehensive insight into the prevalence of weight regain and its associations with clinical outcomes.