Background: Overweight is the fourth most common risk factor for non-communicable diseases (NCDs) in Europe, affecting almost 60% of all adults. In Belgium, as in many high-income countries, average body mass index (BMI) has significantly increased over the past decades. Tackling obesity is therefore vital to reduce premature mortality from NCDs. This study aims to assess the relative contribution of overweight as a risk factor for NCDs and the potential health impact of four BMI reduction scenarios in the Belgian adult population. Methods: Data from the Belgian health interview surveys 2013/2018 (n=18 212) were linked with objective environmental factors based on the residential address. Self-reported BMI and diabetes were corrected based on information from the 2018 Belgian health examination survey and a random-forest multiple imputation process. A G-computation approach was used to calculate the potential impact fractions of four BMI reduction scenarios on diabetes prevalence. The logistic regression model included several confounders related to socio-economic factors, lifestyle and environment. In the first scenario, the BMI distribution among people with overweight was shifted to the BMI distribution of people with “normal” BMI. In the second scenario, the BMI of people with overweight was reduced by one unit. In the third and fourth scenarios, the BMI of people with overweight was modified based on a weight loss of 5 and 10%, respectively. Results: Under the four scenarios, the proportion of diabetes cases prevented would be respectively 29.9% (SE 4.7), 4.2% (SE 0.77), 6.43% (SE 1.48), and 12.5% (SE 2.2). Conclusions: This study highlights the importance of overweight on the diabetes burden. Our results suggest that weight loss intervention programs among people with overweight could significantly reduce the prevalence of diabetes in the Belgian population. Further analyses will be performed for other NCDs and using a larger set of scenarios.