New research presented at this year's European Congress on Obesity (ECO 2026) in Istanbul, Turkey, shows that rapid weight loss (RWL) is much more effective than gradual weight loss (GWL) in both achieving higher weight loss and also sustained weight loss at one year. The study is led by Dr Line Kristin Johnson, Department of Endocrinology, Obesity and Nutrition, Vestfold Hospital Trust, Tønsberg, Norway, and colleagues. The Centre is a collaborating centre with the European Association for the Study of Obesity (EASO) (EASO-COM-Centre), which leads obesity advocacy and education efforts in Europe and organises ECO.
There exist long‑standing beliefs suggesting that rapid weight loss (RWL) is unhealthy and that losing weight very quickly increases the likelihood of weight regain. However, these concerns are largely based on observational data, historical assumptions, or small, methodologically limited studies. Overall, the scientific evidence directly supporting these claims is limited and inconsistent, and high‑quality randomised controlled trial evidence is relatively sparse.
A recent large population-based cohort study , (Busetto et al, 2025), concluded that a body-mass index (BMI) of ≤27 kg/m² and a waist-to-height ratio (WHtR) of ≤0.53 after weight loss may represent clinically meaningful treatment targets for reducing the 10-year risk of obesity-related complications (type 2 diabetes, hypertension, atherosclerotic cardiovascular disease, and hip/knee osteoarthritis).
In this new study, the authors aimed to assess the comparative effectiveness of a rapid weight loss (RWL) program versus a gradual weight loss (GWL) program in achieving these treatment targets.
This 52-week investigator-initiated, randomised clinical trial was conducted as a collaboration between the Department of Endocrinology, Obesity and Nutrition, Vestfold Hospital Trust and Roede AS, one of Norway's leading and most established providers of commercial weight- loss programmes. A total of 284 adults with obesity (BMI ≥30) (257, 90% women) were randomised (1:1) to either a 16-week food-based RWL-program (weeks 1–8: <1000 kcal/day; weeks 9–12: <1300 kcal/day; weeks 13–16: <1500 kcal/day) or a 16-week food-based GWL-program (800–1000 kcal/day below estimated total energy expenditure (with a mean self-reported intake in this group of approximately 1400 kcal/day). Estimated energy expenditure was calculated by estimating the participants' resting energy expenditure and adjusted based on if they had low, medium or high physical activity.
Following the initial weight loss phase, participants in both groups entered an identical 36-week weight-regain prevention programme. The interventions included weekly in-person weight-loss group sessions from week 1 to week 16, and thereafter, in-person group meetings every 14 days for the first 3 months followed by monthly meetings or individual contacts via webinars, video or telephone for the remaining 5 months of the study. In these sessions, participants were advised to increase their daily energy intake by 100–300 kcal during the first month, until weight stability was achieved. Thereafter, daily energy intake was adjusted as needed in response to any concomitant weight changes throughout the 8‑month weight‑maintenance phase. Participants were free to decide whether they wished to maintain their weight or pursue further weight loss. The majority opted for additional weight reduction following the initial 16‑week period.
The food composition in both programs was based on current Norwegian dietary recommendations issued by the Norwegian Directorate of Health ( https://www.helsedirektoratet.no/faglige-rad/kostradene-og-naeringsstoffer/kostrad-for-befolkningen ). Core recommendations included consumption of healthy foods such as vegetables, fruits, whole grains, low‑fat dairy products, fish, eggs, lean meat, and other protein‑rich foods, while limiting the intake of saturated fats and added sugars.
The primary outcome was 1-year percent total body weight loss (%TBWL), and the proportions of participants achieving a BMI of ≤27 kg/m² or a WHtR ≤0.53 after 1 year, were exploratory outcomes. Of the 284 participants, 142 were randomised to the RWL- and 142 to the GWL-program. At baseline, in the RWL-group, the mean age was 48.5 years, body weight 102.4 kg, height 169 cm, BMI 35.8 kg/m², waist circumference 112.5 cm, and WHtR 0.67. Corresponding values in the GWL-group were 47.7 years, 103.0 kg, 168 cm, 36.5 kg/m², 112.8 cm, and 0.67.
During the initial 16 weeks, participants in the RWL-group lost significantly more body weight than those in the GWL-group, with mean %TBWL of -12.9% and -8.1%, respectively, corresponding to a between-group difference of -4.8%. At 1 year, the significant difference was maintained, with mean %TBWL of -14.4%in the RWL-group and-10.5 in the GWL-group, corresponding to a between-group difference of -3.9 percentage points. The proportion of participants achieving a BMI ≤27 kg/m² was significantly higher in the RWL-group than in the GWL-group at both 16 weeks (13.8% vs. 0.8%) and 1 year (28.3% vs. 9.7%). Similarly, a higher proportion achieved WHtR ≤0.53 in the RWL group at 16 weeks (24.2% vs. 8.9%,) and at 1 year (33.0% vs. 18.4%).
The authors conclude: "Among adults with obesity, participation in a structured rapid weight loss program resulted in significantly greater weight loss at 1 year, and higher rates of achieving clinically meaningful BMI- and WHtR targets compared with a gradual weight loss approach. These findings indicate that, when provided within a controlled and professionally supervised setting, rapid weight loss may represent a more effective method than gradual weight loss for reaching key body weight targets associated with reduced obesity-related health risks."
Dr Johnson adds: "Our results clearly challenge the prevailing belief that slow and steady gradual weight loss is necessary to prevent weight regain and reduce obesity-related complications. By contrast, we show that rapid weight loss is not associated with weight regain, and, more importantly, that a larger proportion of participants undergoing rapid weight loss - compared with gradual weight loss - achieved clinically meaningful treatment targets for reducing the 10-year risk of type 2 diabetes, hypertension, atherosclerotic cardiovascular disease, and hip/knee osteoarthritis.
"These findings are particularly relevant given the urgent need for effective weight-loss and weight‑maintenance strategies. As many individuals with obesity cannot access or afford medical or surgical treatments, our results support the potential of effective, commercially available weight‑reduction programs to help reduce the growing burden on public healthcare systems."
