A retrospective pre-post design was used for this study.

Patients with a BMI ≥ 35 kg/m² with comorbidities, or a BMI ≥ 40 kg/m², were referred from the Center for Morbid Obesity in Tønsberg to the lifestyle treatment at the ARRC. Criteria to attend the lifestyle treatment were patients 18 years or older, motivated to change, and those who had tried municipal or local variants of lifestyle treatment options before (22). Patients’ motivation to change was assessed through clinical interviews during intake, while prior attempts at municipal or local lifestyle treatment were evaluated based on their documented health profiles in the healthcare system and referral information. Altogether, 234 patients started the lifestyle treatment before and during COVID-19, but 24 patients (10%) dropped out from treatment during the main stay without providing a reason. Of the 210 patients who completed treatment and liable for inclusion in the study, personnel from the ARRC contacted them via phone to invite participation in this study. A total of 105 patients expressed interest and provided electronic consent. Due to missing data from two patients, the final sample included in the study were 103 patients, resulting in a 50% participation rate. Of these, 53 patients attended treatment before COVID-19 (just before 2019), and 50 patients attended treatment during COVID-19 (in 2020). The inclusion process for patients in this study is illustrated in Figure 1.

The baseline characteristics of the 103 patients who have been included in the study are demonstrated in Table 1.

The lifestyle treatment program at the ARRC was based on recommendations from the Norwegian Directorate of Health (18). A multidisciplinary team consisted of a psychologist, doctor, exercise instructor, clinical nutritionist, physiotherapist, nurse, and coordinator who managed the treatment. Before COVID-19, the program consisted of a nine-week continuous (Monday to Friday; 08:00–15:30) group-based rehabilitation program at the ARRC (see Figure 2). There were three compulsory activities, of which two were physical and one was theoretical. Exercise sessions exceeded 60 min daily and were led by an instructor. Within the week, there were two to three walks, two cycling sessions, and one to three indoor training sessions, with resistance training, a yoga session, and pole walking intervals. Seven nutrition-focused theoretical sessions addressed meal rhythm, portion sizes, and meal planning, emphasizing sustainable weight management. Meals, tailored by nutritionists and adjusted for individual needs, followed Norwegian dietary guidelines (23), with women consuming ~1,600 kcal and men ~1900 kcal daily, distributed across three main meals and three snacks.

Cognitive behavioral therapy, delivered in five sessions by a psychologist, combined behavioral strategies with group work to enhance motivation and promote lasting change. Patients practiced coping strategies and developed planning routines by evaluating weekly tasks related to diet, exercise, and mental health challenges. This approach aimed to foster self-awareness, problem-solving, and long-term lifestyle changes.

During COVID-19, parts of the continuous group-based rehabilitation program at the ARRC were replaced with digital follow-up from home. The program included 5 weeks at the ARRC (weeks 1, 2, 5, 6, and 9) and 4 weeks at home (weeks 3, 4, 7, and 8; see Figure 2). During the home period, patients were required to adhere to a structured timetable, necessitating a high degree of self-discipline. They were responsible for developing a plan that incorporated both dietary guidelines and physical activity. To support this process, a web-based portal (Teachable.co) provided access to timetables, instructional materials, training videos, practical tips, and other resources. Each Sunday, patients completed planning and evaluation forms to track their progress. Additionally, the interdisciplinary team conducted individualized follow-up phone calls every Monday, Wednesday, and Friday. Beyond these scheduled calls, patients could communicate with the team through a secure web-based platform.

After obtaining consent from patients, data was collected from the web-based journal system Extensor Rehab used at the ARRC. Data was de-identified, and all patients were linked to a six-digit code. The material was then extracted in an Excel file that was transferred to SPSS for further analysis. Sociodemographic variables included in the study were age (years), and sex (women/men), which were obtained from the patient’s records. Anthropometrical variables were height in centimeters which was measured at first consultation by a doctor using the Seca 206 measuring device (0–220 cm). For this measure, patients stood barefoot with heels together against the wall with the entire sole of the foot placed on the floor and the body in a straight position. Weight in kilograms was measured by Marsden M-530 (0–300 kg) where the patient was wearing thin and light sports clothes but no shoes. BMI was calculated based on weight divided by the square of height in meters (kg/m²). Physical Activity levels were measured with a Functional Threshold Power (FTP) test carried out in a spinning room on a TOMAHAWK IC7 indoor bike with an instructor. The result is measured by energy per unit of time with measure watt (W) defined as one joule per second (1 J/s) (24). HRQoL was assessed by the European Quality of Life 5 Dimensions 5 Level Version (EQ-5D-5L), a widely used generic tool developed by the European Quality of Life Group (25). It has been shown to have good validity and reliability as a measure of HRQoL (26). EQ-5D-5L is divided into five dimensions: walking, personal care, usual chores, pain/discomfort, and anxiety/depression. In each of these categories, patients gave a rating on a five-point scale, where 1 equal “no problems” and 5 corresponds to “major problems.” The patient’s self-assessed health was also reported on a visual analog scale (VAS score) numbered from 0 to 100, where 100 indicates the best.

The Regional Committee for Medical and Health Research Ethics in Central Norway (REK) approved the study (REK reference number 211470) and patients signed a digital informed consent.

Statistical analyses were carried out in Statistical Package for the Social Sciences (IBM SPSS Statistics) version 28. Descriptive data were presented with means (SD) and numbers (%). Repeated student’s t-test was used for the continuous normally distributed variables. For the non-normally distributed continuous variables, the Wilcoxon-Mann–Whitney test were used. The significance level was set at 5% (p < 0.05). Multiple imputation in SPSS was used to impute the missing variables. The method estimates the missing values in the dataset based on the remaining variables in the analysis model. When the proportion of missing data is low (≤5%), this method is considered fairly accurate (27).

Our study found that while both groups experienced improvements in HRQoL, patients who attended treatment before COVID-19 reported higher HRQoL scores compared to those who attended during the COVID-19. This suggests that other factors specific to the pandemic period may have negatively impacted their quality of life. Our findings align with previous research showing that the COVID-19 stay-at-home order was associated with significant mental health challenges among individuals with obesity (11, 12, 28). Research indicates that 73% of patients receiving care from both an obesity medicine clinic and a bariatric surgery practice reported heightened anxiety, 84% experienced increased depression, and 70% faced challenges with weight management during the pandemic (11). Additionally, pandemic-related concerns could have influenced HRQoL. Early in the pandemic, individuals with obesity were believed to have a higher risk of severe COVID-19 outcomes (29), a concern later confirmed by studies showing increased risks of infection and mortality (30).

In addition, disruption in social support could be another possible factor that may have affected HRQoL among the patients during the COVID-19 pandemic. Societal restrictions and recommendations to reduce social contact during the pandemic may have disrupted essential social support from family and friends, especially during home-based treatment phases (31). Social support is a key motivator for successful weight loss and maintenance, with group-based approaches often outperforming solo methods—where individuals undertake the effort independently or with minimal external, structured support—as well as one-to-one methods (32). Humans, as social beings, tend to address challenges more easily within a supportive, secure group environment (33). Group-based conservative treatment, which includes education and group training sessions with like-minded individuals, has been shown to enhance motivation and coping skills (34). At the rehabilitation center, mandatory participation in educational and physical sessions provided structured support and facilitated group interaction, likely contributing to increased motivation and coping capacity among patients. In contrast, home-based components of the treatment during the pandemic required greater self-discipline on the patients’ side, potentially lowering HRQoL outcomes. Moreover, patients who did not adhere to PA or dietary plans may have felt less capable of coping, further reducing HRQoL. Future studies should explore lifestyle treatments that integrate mental health support and social connections, particularly during periods of social restrictions.

Both groups in our study showed improvements in PA levels, measured by functional threshold power. This aligns with previous research demonstrating increased physical fitness among patients with obesity attending lifestyle treatment (35). The COVID-19 lockdowns, as noted in other studies (11, 12, 36), disrupted exercise routines, leading to a decline in PA levels, increased sedentary time, and more time spent in bed during weekdays. This may explain the disparity in PA levels between our study groups before and during pandemic. A study examining the effects of COVID-19 stay-at-home orders on weight-related behaviors in patients with obesity found that the pandemic had a significant impact on these behaviors. Patients experienced a reduction in intensity and duration of PA, along with difficulties in achieving weight loss goals, regardless of infection (11). In another study exploring the challenges of weight management and improving lifestyle treatment during COVID-19, participants reported that stress and anxiety caused by stay-at-home orders further hindered adherence to weight management programs (15). An online survey comparing PA levels before and during COVID-19 pandemic found that people with obesity were disproportionately affected, experiencing a decline in PA, a shift toward lower-intensity activities, and increased sedentary behavior, especially on weekdays (13). Secondly, the program structure likely influenced the disparity in PA levels between groups in our study. The before-pandemic group attended all mandatory classes and daily supervised exercise sessions, promoting better adherence and improvement in PA. In contrast, the COVID-19 program’s at-home component relied on patient self-discipline, making it harder to maintain consistent exercise. Such challenges are supported by research indicating difficulties with self-directed exercise, particularly for individuals with weight management goals (37). Furthermore, existing knowledge aligns with the understanding that, while exercise may not be the most effective initial weight loss strategy, consistent exercise is a crucial factor for long-term weight maintenance success and cardiovascular health (38). Altogether, the structured and supervised environment of the before-COVID-19 program likely facilitated the development of sustainable exercise habits, contributing to the observed greater improvement in PA levels.

Given the observed differences in PA levels, it is important to consider how these differences may relate to HRQoL among individuals in our study. Increased isolation during home confinement has been unfavorable for patients with obesity, contributing to reduced PA and further decline in HRQoL (39). Physical fitness—often as a proxy for PA—may reduce obesity-related mortality and improve both physical and mental aspects of quality of life, even if its link to weight loss is less clear (14, 20, 28). In our study, patients who attended treatment before COVID-19 with higher PA levels demonstrated greater HRQoL scores compared to those who showed lower PA improvements during the pandemic. This aligns with the existing literature (40), which suggests that even a slight improvement in PA can enhance HRQoL in individuals with obesity. However, the relationship between PA and HRQoL is complex (14, 41). While one study supports our findings by demonstrating an association between PA and HRQoL (14), another suggests that the impact of PA varies across different dimensions of HRQoL. For instance, one study revealed that PA primarily improves the physical aspects of HRQoL but has limited effects on the mental aspect of it, particularly in individuals undergoing obesity treatment (42). Conversely, one study (41) reported no significant improvement in HRQoL following structured PA interventions, highlighting that factors beyond PA such as psychological or lifestyle factors, may play a crucial role in determining HRQoL outcomes. Moreover, one study has found that lifestyle interventions lead to notable improvements in quality of life (43).

Both our findings and existing literature (14, 41), underscore the intricate relationship between PA, mental health, and HRQoL in people with obesity, particularly within the context of the COVID-19 pandemic. The pandemic exacerbated mental health challenges, reduced PA levels, and negatively affected HRQoL (11, 12), reinforcing the need for comprehensive, socially supportive lifestyle treatments. However, as this study was a natural experiment without randomization, we cannot fully exclude the possibility that other external factors contributed to the observed differences. Future weight management strategies should prioritize structured, accessible, and guided interventions that address self-discipline challenges and promote long-term health maintenance.