Introduction
Due to generally excellent results in terms of weight loss, improvements in health-related quality of life (HRQoL), and reduction in overall mortality and morbidity, bariatric surgery is considered the best treatment option for extreme obesity [
1,
2]. However, in the long-term, these results are not maintained in all patients. There is growing recognition that weight regain is a concern after bariatric surgery [
3‐
8]. Weight regain has been associated with deterioration in HRQoL, the re-emergence of type 2 diabetes and other comorbidities, and patients’ opinion about surgery success [
3,
4,
9‐
11].
The key studies focusing on long-term outcomes after bariatric surgery show that patients generally regain 5 to 10% of their total weight loss (%TWL) within the first decade [
2,
6,
12]. In the Swedish Obese Subjects (SOS) study, the first large, long-term prospective study, %TWL decreased from 32 to 25% within 10 years after Roux-en-Y gastric bypass (RYGB) [
2]. In the Longitudinal Assessment of Bariatric Surgery (LABS) study, %TWL decreased from 35 to 28% within 7 years after RYGB, and in another large long-term study with a high follow-up rate (90% up to 12 years), %TWL decreased from 35 to 27% within 12 years after RYGB [
6,
12]. Thus, it seems that some weight regain after bariatric surgery is common. However, different weight loss trajectories were observed and a subgroup of patients regains a significant amount of weight and experiences associated problems [
12].
Estimates of the percentage of patients who regain a significant amount of weight vary widely [
4‐
8]. In a systematic review among 16 studies, weight regain rates ranged from 19 to 87% for patients who underwent RYGB and sleeve gastrectomy (SG), while a systematic review among 21 studies found weight regain rates after SG ranged from 6 to 76% over variable follow-up periods ranging from 2 to 6 years [
4,
5]. Both reviews report great variability in assessment methods of weight regain among the included studies. This wide variation arises from the lack of consensus on the definition of weight regain. Many different, arbitrary definitions of weight regain are currently found in the literature [
10]. These definitions include, but are not limited to: “any weight regain,” the percentage of total weight lost at nadir, the percentage of excess weight loss (%EWL), the percentage of weight change from nadir, or a minimum increase in kilograms [
3,
5,
8,
13‐
21].
Only two studies have compared measures of weight regain, by applying a number of different definitions of weight regain to the same post-bariatric cohort [
8,
10]. Both studies found that the definition of weight regain drastically changed the reported outcomes. The first study applied six different definitions of weight regain to a small cohort (
n = 55) of patients 5 years after SG. This led to weight regain rates ranging from 9 to 91% [
10]. The second study applied five continuous and eight dichotomous measures to a large cohort of 1406 RYGB patients from the LABS-2 study, who were followed up until 5 years after surgery. Weight regain rates according to the eight dichotomous measures ranged from 44 to 87%, depending on the definition applied [
8]. In this study, weight regain measures were also related to other clinical outcomes, such as diabetes.
Thus, studies on the definition of weight regain are still inconclusive. In addition, weight regain rates have not been explored in a European sample, nor in a sample including patients who have either undergone RYGB or SG. Further exploration of the associations of different definitions of weight regain with clinical outcomes is needed to develop a clinically relevant definition [
10,
22]. Such a definition will help identify patients who experience weight regain and make it possible to investigate mechanisms causing long-term weight regain, thereby ultimately enhancing long-term treatment outcome.
To examine these issues more thoroughly, this study aims to replicate previous findings regarding weight regain prevalence 5 years after primary SG or RYGB, by applying six different definitions of weight regain, as applied in an earlier study, in a large cohort of bariatric patients [
10]. Moreover, the clinical relevance of these definitions was determined by investigating which patient characteristics, such as demographic information, baseline BMI, and surgical procedure, were related to definitions of weight regain and by investigating the relationship between definitions of weight regain and HRQoL and comorbidity resolution at 5-year follow-up. We hypothesized that (1) the definition largely determines long-term weight regain prevalence; (2) the characteristics of patients who regain weight differ across definitions of weight regain; and (3) associations between weight regain and HRQoL and comorbidity resolution will vary by definition used.
Discussion
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 [
10]. 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 [
8]. 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 [
7]. 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‐
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‐
35].
Interestingly, age was inversely related to weight regain, which has been described previously [
13]. 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 [
36]. 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‐
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 [
41]. 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 [
8]. 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 [
24].
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 [
34]. 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 [
42]. 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 [
43]. 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.
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