Adipositas Care and Health Therapy (ACHT) after Bariatric-Metabolic Surgery: A Prospective, Non-Randomized Intervention Study

The prevalence of adults with overweight or obesity has increased dramatically in Western societies. In Germany, there are 50% of adults with overweight and almost 25% with obesity [1]. Alarmingly, 2.8% of women and 1.2% of men already suffer from obesity (body mass index [BMI] > 40 kg/m²) [1]. An increase in the severity and duration of obesity is associated with an increased risk of various diseases such as type 2 diabetes, cardiovascular disease, mental health problems, musculoskeletal disorders, and cancer [2]. Obesity can lead to social stigmatization, which in turn can lead to depression and a reduced quality of life. Due to the high costs of secondary and concomitant diseases [3], obesity is one of the greatest health economic challenges of the 21st century. Effertz et al. [4] (2016) estimate the direct annual costs of obesity in Germany (doctor’s visits, medication, etc.) at EUR 29.4 billion; and the indirect costs, e.g., due to sick leave, at an additional EUR 33.7 billion.

Bariatric-metabolic surgery is currently the most effective treatment for obesity [5, 6]. It significantly reduces weight and comorbidities, such as type 2 diabetes mellitus. In Germany, however, bariatric surgery is performed relatively rarely compared to other Western countries. In 2022, about 28,800 bariatric surgeries (OPS codes 5-434 and 5-445) were performed on persons between the ages of 20 and 70 [7], which corresponds to the rate mentioned by Fink et al. [8] for 2019. Strict rules for reimbursement are one reason for this low number, although there are clearly defined indications for bariatric-metabolic operations as outlined by the German S3 clinical guideline [9].

Bariatric-metabolic surgery requires long-term follow-up and lifelong care by an interdisciplinary team [10]. This ensures surgical success and postoperative problems, such as surgical complications or malnutrition are either prevented or detected at an early stage. Although the need for long-term follow-up is stipulated in national and international guidelines [11, 12], in Germany, this follow-up is currently not standardized, not integrated into outpatient care structures, and not adequately funded [11, 13]. Currently, most large obesity centers have established some follow-up care, as certification rules require respective structures. Considering the rising prevalence of bariatric surgery, the lifelong need for follow-up care and cost pressures faced by obesity centers, the current situation is neither sustainable nor does it meet standards of care. Furthermore, nutritional counseling and therapies recommended by guidelines [14] are not systematically offered. In many cases, long distances between the patient’s home and the surgical center (usually only in larger tertiary hospitals) further hinder the continuity of follow-up care. Also, there is no uniform standard of follow-up, even at specialized centers. Thus, establishing a structured follow-up care program would further ensure long-term therapeutic success [15].

The overarching aim of the ACHT (Adipositas Care & Health Therapy) study is to evaluate the improvement of the long-term therapeutic success of patients with obesity after bariatric-metabolic surgery through structured and cross-sectoral follow-up care. The primary goal of the study is to examine the effects of the 18-month ACHT follow-up program on the health status of patients after bariatric-metabolic surgery compared to usual care. Also, the effects on quality of life, depression and postoperative nutritional deficiencies, adherence to therapy and compliance with follow-up appointments will be examined. The ACHT study is funded by the German Federal Joint Committee through the Innovation Fund (G-BA: 01NVF18023) for 4.5 years.

ACHT is a prospective, non-randomized control group study. Due to the limited time frame of the study grant, long-term effects are difficult to assess. To allow inferences about longer term effects, we simulate a longer intervention period by assessing two identical but time-shifted intervention arms. The first group – the early intervention group – begins the 18-month ACHT follow-up program within 3 weeks (+/− 10 days) after bariatric operation. The second group – the late intervention group – starts the program 18-month post-surgery (shown in Fig. 1).

Study centers were recruited in 2019, from all bariatric surgery centers in Bavaria, who were either certified by the German Society for General and Visceral Surgery (DGAV) or qualified for certification.

Participating study centers are responsible for recruiting participants. Patients who had undergone bariatric-metabolic surgery (gastric sleeve or Roux-en-Y gastric bypass) at one of the study centers are eligible to participate in the study if they fulfill the other inclusion criteria (see below). The bariatric case managers (BCMs) review the available patient files of their respective centers to select potential participants and consequently contact all eligible patients. Since follow-up care of patients in the intervention group was linked to participation in a selective contract (§ 140a SGB V) of the participating health insurance company (AOK Bayern), only patients insured by this company were eligible to participate in the intervention groups. As shown in Figure 1, three cohorts are defined based on the time of surgery and form four study groups. Intervention group 1 (“early intervention”) includes postoperative patients who start the 18-month postoperative follow-up 3 weeks (+/− 10 days) after undergoing surgery (months 1–18). Those fulfilling the inclusion criteria for the early intervention group are contacted and informed 2 weeks before their surgical procedure. Already during their hospital stay at the time of the operation, the BCM approaches the patient and inquires about their interest in participating. Finally, the patients are enrolled in the study 3 weeks after surgery. Control group 1 is recruited from postoperative patients who underwent their bariatric-metabolic surgery 18 months prior to the point of evaluation but thus far only received standard care. Participants for control group 1 are contacted about 17 months after their surgery. Intervention group 2 (“late intervention”) is recruited from participants of control group 1 and included patients who agree to participate in the 18-month follow-up intervention (months 19–36 postoperatively). Control group 2 includes postoperative patients who underwent bariatric-metabolic surgery 36 months prior to agreeing to a single follow-up evaluation at the study center (month 36 postoperatively). Participants for control group 2 are contacted about 34 months after their bariatric surgery. Specific inclusion and exclusion criteria are described in Table 1. Evaluation of control groups 1 and 2 are compared to the final evaluations of intervention groups 1 and 2, respectively. All recruitment was completed in November 2022.

The ACHT follow-up program aims to provide structured, cross-sectoral, digitally supported, close-to-home follow-up care to adults following a bariatric-metabolic operation and thereby improve the health status of patients after bariatric-metabolic surgery. This includes improving quality of life, addressing depression, and reducing postoperative nutritional deficiencies. In addition, ACHT aims to strengthen postoperative care in the outpatient setting and improve exchange between the outpatient and inpatient sectors as well as patient adherence to therapy by using the ACHT obesity app, an electronic patient record and motivation through a BCM. In the long term, ACHT aims to contribute to reducing indirect costs caused by sick days or early retirement due to disability. External experts, e.g., patient representatives, and representatives of the various professional groups, were involved in the planning and implementation of the program to prioritize the relevant elements and establish a basis for acceptance. The following eight components were implemented in the follow-up program:

• Structured, close-to-home follow-up care in specially trained “ACHT outpatient practices”: comprehensively trained nutrition or diabetes practices provide regular health assessments following standard operation procedures (SOPs) (including physical and special laboratory exams), therapy adjustments, patient education, and nutritional advice. They apply standardized checklists to identify postoperative problems and initiate targeted medical investigations and therapy at an early stage. This includes adjusting medications for diabetes, hypertension, and other comorbidities. The SOPs and checklists were developed by an interdisciplinary team of experts and evaluated by an external advisory board. As a prerequisite, these practices must successfully complete an online training course, and must meet equipment requirements, e.g., scales for persons up to 250 kg of weight, and an ultrasound machine (or the possibility to promptly refer patients). They must also cooperate with a nutritionist.

• The BCM: In each study center, a dedicated BCM was appointed. The main task is to accompany and guide the patients through the program. The BCM is the central coordination point between the obesity surgical centers and the outpatient follow-up practices. The BCM is also the central contact person for the patient as well as coordinates the entire follow-up process and has an important monitoring and motivational function. Through the patients’ entries in the app, the BCM monitors their progress, their adherence to the therapeutic protocol as well as physical complaints. Via the app (or by phone), the BCM has regular contact with all patients from the respective center. In addition, the BCM organizes the evaluation examinations.

• The ACHT obesity app: a specifically developed obesity app acts as a patient interface to fully involve patients in their follow-up care. The app enables patients to document daily important information regarding their mood, physical complaints, drug and dietary supplement intake, nutritional behavior and protein intake, exercise, and step count. Body weight was documented once a week. The data are then transferred to the electronic patient record and used by the BCM to assess the patient’s health and the course of therapy in real time. The composition of the parameters depends on the individual therapy goals for the patient. In addition, the app displays the patient’s individual therapy goals and further supports patients with useful reminders, especially regarding practice appointments. As mentioned above, the app allows a direct contact between the patient and the BCM, which is particularly helpful in case of physical or psychological problems.

• Electronic patient record: The electronic patient record is used to exchange information and knowledge by linking all relevant actors of the treatment process (obesity center, ACHT outpatient practice, nutritionist, sports physician). It focuses on the interdisciplinary and intersectoral connection of all treating therapists within a patient’s network. It integrates the results of all examinations from the initial evaluation until the end of the study. The patient file contains a role-based user concept. Patients explicitly permit involved therapists to access their data according to the independently approved data protection regulation.

• Regular nutritional counseling: during their follow-up appointment in the ACHT practice, patients are also counseled by a nutritionist, who defines the individual nutritional goals for the patient. SOPs for nutritional counseling were developed to ensure comparable content and quality for all patients within ACHT. Throughout the follow-up process, the therapy goals are regularly evaluated. If necessary, reasons for not reaching therapy goals are identified, discussed, and goals adjusted accordingly.

• Tailored exercise program by sports physician: the ACHT follow-up program includes two visits to a sports physician. Based on a medical examination and accounting for individual restrictions, the sports physician sets individual exercise goals for the patient. The tailored sports program is then reevaluated and adjusted after 6 months. Checklists and SOPs ensure a comparable quality for all patients.

• Psychological stabilization of the patient: to stabilize and support patients’ mental health, ACHT uses several mechanisms throughout the program. The initial evaluation included several questionnaires on mental health to identify patients at risk immediately. Each obesity center has access to a board-certified psychiatrist if professional support is needed. The BCM is also ensuring psychological stability by monitoring patient’s entries in the app and intervening if necessary. Furthermore, a dedicated psychologist is part of the local team of the coordinating center and supports all study centers (including a weekly supervision of all BCMs by video call).

• Integration of the quality assurance measure StuDoQ: systematically monitor the quality of surgical obesity therapy, a national obesity register was established in 2015 as part of the StuDoQ initiative of the German Society for General and Visceral Surgery (DGAV) [12]. Every certified obesity center must use a standardized electronic mask to document the patient’s basic data, the preoperative preparation, the perioperative course, and the patient’s follow-up care. The clinical data collected as part of the ACHT study are coordinated with this StuDoQ register.

The intervention consists of 18 months participation in the ACHT follow-up program described above and by the schedule shown in Figure 2.

The surgical obesity centers perform the evaluation tests that are identical for all groups and time points. The evaluation at the end of the study is complemented by a questionnaire to explore participants’ satisfaction.

The primary endpoint is the general health of the patients after 18 months in the ACHT follow-up program as measured by the modified King’s score [16‒18] compared to the corresponding control group. The score was initially developed at King’s College to assess obesity and comorbidities of obesity. The criteria were originally defined in Whyte et al. [18]. For this study in Germany, some criteria were slightly adapted to allow reliable evaluation after bariatric surgery and in order to minimize inter-observer variability. BMI classes used to define normal state to advanced disease were adjusted since this is a follow-up study and does not assess the need for surgery. The modified King’s score contains 12 criteria each subdivided in 4 categories indicating the extent of the disease (0 healthy – 3 advanced disease) allowing the calculation of a total score between 0 and 36 points. The exact criteria are shown in Table 2 combined with the instruments used to assess the criteria. Originally, criteria were only considered individually. However, in this study, we primarily consider the sum of the criteria.

Secondary endpoints are summarized in Table 3. They include comparisons of health between the intervention and the control groups regarding quality of life, anxiety, depression, the individual dimensions of the King’s score, cardiovascular status, (symptoms of) nutritional deficiency, complications of surgery and sick days. Other secondary endpoints examine process variables in the intervention group and achievement of benchmarks (pre-stipulated goals) regarding adherence and satisfaction. Furthermore, structural effects regarding app and electronic patient file use and location of care are also assessed as are patient costs and costs of the intervention program. Unless otherwise stated, the endpoints are evaluated at 18- or 36-month post-surgery.

The primary endpoint, the King’s score, will be compared between the intervention and control groups in a confirmatory cross-sectional analysis using multivariate regression adjusting for confounders such as age, sex, type of surgery, surgical center, and other available information. Comparisons of early and late intervention groups will be performed separately. In a sensitivity analysis, we will also adjust for a propensity score. Since the study intervention is only available to participating patients, it can be assumed that any measured effects can be attributed to the complex intervention. Thus, the primary evaluation of the endpoints will be performed as an “intention to treat” analysis, which accounts for group allocation without considering adherence to the study protocol.

Secondary endpoints will be examined in exploratory evaluations. Changes in these endpoints can only be examined in the intervention groups. However, several endpoints (such as BMI or quality of life) are also collected within the StuDoQ database and are, therefore, available for the controls, as well. Thus, further comparisons of the changes within the controls and the intervention groups will be made.

The effects of the intervention on structures of care and care processes will be examined with exploratory analyses of the intervention groups. Descriptive analyses and multivariate regression analyses will be used to identify possible determinants.

To evaluate healthcare costs associated with bariatric-metabolic surgery and the intervention, health insurance billing data will be used. One dataset will include patients who had bariatric-metabolic surgery in the 3 years prior to the start of the study. Another dataset will include healthcare billing data of patients who are enrolled in the study and insured by the participating health insurance company (AOK Bayern). Both datasets will be used to calculate healthcare costs. Since participants in both intervention groups and control group 1 must be insured by the participating health insurance company, their billing data will be available. Healthcare costs per patient in intervention group 1 and control group 1 over 18 months can be compared with regression analyses to examine the effect of the follow-up program. Furthermore, utilization of medical services, costs according to comorbidities, and changes in the proportion of the types of surgery will also be characterized. The costs of patients who had bariatric surgery in the 3 years prior to the start of the study will be used to calculate average time-dependent costs relative to the bariatric surgery. These may be useful for estimating healthcare costs of controls of the late intervention. Comparing costs in addition to other parameters, such as quality of life or depression will provide a more complete picture of the intervention.

Finally, program costs of the intervention will be determined based on resource utilization for the BCM and for setup and maintenance of the app and actual reimbursement through the special contract. These costs reflect the resources required for incorporation into usual care.

The sample size calculation was based on the comparison between intervention group 1 (early intervention) and control group 1 regarding the primary endpoint (general health status measured by the King’s score). There are currently no published data on the King’s score for Germany. However, using published data for patients after bariatric-metabolic surgery in London [19, 20], we estimated an average modified King’s score after surgery of 4.15 (Roux-en-Y gastric bypass) (standard deviation: 2.45). For the gastric sleeve operation, King’s score data were not available. According to an expert survey of 11 German and international obesity experts, a difference of 1.75 points between intervention and control groups was expected to be clinically relevant. Thus, to achieve 90% power at a significance level of 5% (two-sided test) and an expected “lost to follow-up” rate of 10% for intervention group 1, a total of 220 patients is needed to prove this difference of 1.75 points. Therefore, the aim was to include 110 patients in intervention group 1. When calculating the number of cases for intervention group 2 (late intervention), a higher “lost to follow-up” rate of 20% was assumed. Therefore, intervention group 2 should contain a total of 140 patients.

The estimation of the control group sizes must also consider the calculation of the number of cases for intervention 2. To have an adequate number of participants for the comparison and an increased informative value of the propensity score, a size of 180 patients is aimed for both control groups.

All national and international guidelines strongly recommend long-term follow-up of patients after bariatric-metabolic surgery because patients are at risk of developing postoperative surgical complications and malnutrition but also of regaining weight [11, 13]. However, in Germany, this follow-up is currently not standardized and not properly financed [11, 13]. Thus, patients largely depend on the follow-up program offered by the respective obesity center and close-to-home follow-up care is rare. To alleviate this problem, the ACHT consortium has established a structured program, in which patients are mainly treated by local physicians with remote support from obesity centers. The ACHT study now examines the effectives of this intervention in ensuring long-term therapeutic success after bariatric-metabolic surgery. Specifically, its effects on physical and mental health, quality of life, adherence to therapeutic goals and costs will be explored. The intervention tested in this study, the ACHT follow-up program, offers a digitally supported, structured, cross-sectoral, and close-to-home follow-up program for patients after bariatric-metabolic surgery, which will be scientifically evaluated.

A major strength of this study is that it allows an evaluation of a structured, cross-sectoral follow-up program after bariatric surgery. Since many postoperative complications may occur after bariatric surgery, implementation of a structured management program, supported by an ACHT obesity app and an electronic patient record, may enhance cross-sectoral care, improve outcomes, and be a good model for other healthcare settings. Evaluation of important parameters and comparing these between control and intervention groups will allow evidence-based conclusions to be drawn. Furthermore, patient adherence to the program and satisfaction with the program will indicate which features of the program are important. If successful, the intervention can easily be transferred to other centers and other regions in Germany. Since it is anticipated that the demand for bariatric surgery will increase and since the program includes the perspectives of relevant stakeholders, such as a statutory health insurance company and the Bavarian Association of Health Insurance Physicians, a high level of acceptance by physicians, expert surgical centers, and patients is to be expected. With all these stakeholders on board, it should be straight forward to implement the program – in case of success – in the German health system.

Another important strength of this study is the evaluation of health and economic outcomes of the structured postoperative care program. Due to the limited financial resources in the healthcare system, it is important not only to show the effects on health and patient-related outcomes but also to show the effects on healthcare costs. In addition to patient costs, this study evaluates the program costs of the intervention and the required resources such as staff are determined to obtain information about the resources required in routine practice. Moreover, ACHT considers the principle of “outpatient before inpatient” which ensures patients are treated in their familiar environment and care is carried out economically. Finally, ACHT will be evaluated by independent scientists from an institution not involved in patient care of the investigated study.

An obvious limitation of our study is the lack of randomization (or cluster randomization), which was not possible due to numerous factors. The limited duration of project funding led to the decision that the longest possible follow-up care period was important for the intervention patients, leaving only a short recruitment time specifically for this group. Thus, long-term effects cannot be examined directly but are examined indirectly by recruiting early and late intervention groups. Furthermore, a disadvantage of simple randomization could be the spillover of effects in the practices from the intervention to the control groups. Another limitation is that patients receiving the intervention had to be insured by the participating health insurance company (for reimbursement of the follow-up program) and must have been operated in a predefined time-period in a participating center. The number of patients fitting all requirements and insured by the participating health insurance company was insufficient to provide adequate power for both intervention and control groups. Selecting intervention patients from only one health insurance company may increase the risk of selection bias, which will be addressed by inclusion and exclusion criteria and adjusting for patient characteristics in the regression analyses.

There may also be a risk of response bias, as participants are recruited from various obesity centers which may differ in who or how they address their patients for the study. This bias will be counteracted by adjusting for study center, using standardized operating procedures and questionnaires, in-depth personnel instructions, and training, as well as having weekly meetings between the project managers and the BCMs.

As only patients of the participating health insurance company can participate in the ACHT study, the sample may not be representative. Persons insured by different health insurance companies may differ regarding education, income, and socioeconomic status, and also regarding surgical methods, procedures, and the frequency of operations. However, the participating insurance company insures about 40% of all inhabitants of the state Bavaria [21]. Furthermore, patients who receive a bariatric-metabolic operation are selected according to standard guidelines. Therefore, it is assumed that there are only minor differences between health insurance companies regarding this patient population. Also, patients in the late control group will be recruited from other health insurers. This allows a general check of the representativeness of the sample. Limiting the type of operation to gastric sleeve or gastric bypass surgery further reduces differences between the control group (from other health insurances) and the intervention group for the late comparison. Also, a comparison of patient characteristics to national [22‒26] and international literature [22, 27, 28] will allow an assessment of whether study patients are representative. Recall bias could affect information on sick days, which are self-reported by patients, but a plausibility check is possible by comparing patient responses with health insurance data.

The COVID-19 pandemic had serious consequences for the entire healthcare system, but especially for the lives of chronically ill patients [29, 30]. An important factor to consider in the study design is the impact that the COVID-19 pandemic could have on the study outcomes, especially whether the chosen historic control groups are comparable to the intervention groups. The literature suggests that the COVID-19 pandemic resulted in less weight loss [31‒33] after bariatric surgery. Furthermore, patients decreased their physical activity [34‒36], had poorer nutrition [34‒37], and had difficulties accessing follow-up care [38]. Many of the patients included in this study had at least parts of their follow-up care during the COVID-19 pandemic. Hence, it is reasonable to assume that study participants were negatively affected by the pandemic. Since the exposure to the pandemic might have differed significantly between our intervention (more) and control (less) groups, the COVID-19 pandemic constitutes an unanticipated threat to the internal validity of our study design. However, if so, the pandemic should bias our results toward a null effect which means that we underestimate the effect of our intervention.

In summary, this study evaluates the effectiveness of a structured, close-to-home and cross-sectoral follow-up program, which includes digital support for patients and caregivers after bariatric-metabolic surgery in ensuring a better clinical outcome for the patient than usual care, while the costs remain the same or even could be reduced. The results of this study should support future decisions on whether the implementation of this new postoperative concept is useful and feasible in routine practice.

We would like to sincerely thank the ACHT team for their commitment to the ACHT project: Dr. Philipp Kahle, Samira Omairat, Pia Hengge (Dr. Lubos Klinik Bogenhausen), Dr. Min-Seop Son, Vanessa Keller (WolfartKlinik München-Gräfelfing), Dr. Miljana Vladimirov, Veronika Gradl (Klinikum Nürnberg), Dr. Heinz Schlosser, Verena Meusel (Klinikum Memmingen), Dr. Klaus Gerauer, Dr. Charlotte Bamberger, Sabrina Maaβen (Klinikum Passau), Prof. Dr. Thomas Horbach (Viszera Chirurgie-Zentrum München), Jakob Lauerer (Universätsklinikum Würzburg), Dr. Andreas Wierlemann (Main-Klinik Ochsenfurt), Dr. Hans-Jörg Hellmuth (Familienarztpraxis Dres. med. Hellmuth & Frieling GbR) Florian Güntner, Dr. Sabine Korger, Meike Müller, Margit Hermann (AOK Bayern), Ursula Chmiela, Ramona Gaube (KVB), Carsten Klinger (DGAV), the team of the vitagroup and the members of the ACHT advisory board.

This study protocol was reviewed and approved by the University of Würzburg Ethics Committee, Institute for Pharmacology and Toxicology, Versbacher Str. 9, 97078 Würzburg, Germany, approval number 191/19. This study was conducted in accordance with the 1964 Helsinki Declaration and its later amendments. Written informed consent was obtained from all individual participants included.

Oliver Martini is employed by Johnson & Johnson. The other authors have no conflicts of interest to declare.

This work is supported by the German Federal Joint Committee through the Innovation Fund, with the grant number 01NVF18023.

Renee Stark: writing of first draft of manuscript and revisions and development of evaluation concept; Anna Renz: co-development of study SOPs and co-writing of first draft of manuscript and revisions; Michael Hanselmann: contributed to the discussion of the manuscript; Christina Haas: co-development of the study SOPs; Anne Neumann: revision of the manuscript; Oliver Martini: initiation of the Innovation Fund Project application and content support during the concept phase; Florian Seyfried and Christine Stier: co-development of the ACHT follow-up program; Michael Laxy: co-development of evaluation concepts and revision of the manuscript; Bettina Zippel-Schultz: fund raising, co-development of the ACHT follow-up program, SOPs, and revision of the manuscript; Martin Fassnacht: fund raising, co-development of the ACHT follow-up program, and revision of the manuscript; Christina Haas: co-development of the ACHT follow-up program and revision of the manuscript; and Ann-Cathrin Koschker: co-development of the ACHT follow-up program, SOPs, operationalizing of the King’s score, and revision of the manuscript. All authors have approved the final version of the manuscript.

Trial Registration: ClinicalTrials.gov Identifier: NCT04768127.

All relevant data are available within the manuscript and in the submitted figures and tables. Further inquiries can be directed to the corresponding author. Furthermore, the German Federal Joint Committee is funder of this project and will also publish the final outcomes.