Background: Reformulation policies have been implemented to improve the nutritional quality of diets through the modification of the food offer. To assess the potential effects of reformulation policies, past research analyzed the impact of interventions in specific food sectors or for specific nutrients, using generally theoretical approaches. This study used branded food composition data to model potential effects on dietary intakes of widespread reformulation based on the composition of existing products. Methods: Dietary data were retrieved from the Nutrinet-Santé cohort at inclusion (N=100,418), providing detailed information regarding participants’ diet (N>3,000 unique generic food items). Each food consumed was matched with data from OpenFoodFacts, providing composition information from the French food market (N=119,060 products used) and products were classified as low, medium, or high quality for each generic food item according to FSAm-NPS. Three scenarios were constructed: a baseline scenario in which products were selected from the entire range of food, two counterfactual scenarios with a food selection restricted only to products of higher nutritional quality, or poorer nutritional quality. For each scenario, a product of the corresponding selection was randomly attributed to each individual and dietary intakes were then assessed. Results: We found that substitution from overall to products of higher nutritional quality led to improvement in diets for energy (-55 kcal/day,-2.9%), saturated fat (-2.4g/day,-7.6%), sugar (-4.8g/day,-5.3%) and salt (-0.54g/day,-8.3%) intakes. Improvements in diet quality were observed across all population strata. Food groups for which changes in composition contributed the most to improvements at the population level were: 1) sweets/confectionary, sweetened beverages, biscuits for sugars; 2) dairy desserts, processed meats, biscuits for saturated fat; 3) breads, cheeses, prepared dishes for salt. Conclusions: Our study showed that replacing food consumed by similar one (intra-group substitutions) with different composition allows to substantially improve the overall quality of the diet.