Identifying the dietary changes with the greatest potential for improving diet quality is critical to designing efficient nutrition communication campaigns. Our objective was to simulate the effects of different types of dietary substitutions to improve diet quality at the individual level. Starting from the observed diets of 1330 adults participating in the national French Nutrition and Health Survey (Etude Nationale Nutrition Sante), we simulated the effects of 3 different types of food and beverage substitutions with graded implementation difficulty for the consumer in a stepwise dietary counseling model based on the improvement in the PAN Diet index, which measures diet quality in terms of nutrient adequacy. In scenario 1, substitutions of a food or beverage for its "lighter" version resulted in a modest improvement in the PAN Diet score (Delta = +3.3 +/- 0.1) and a decrease in energy intake (Delta = -114 +/- 2 kcal/d). In scenario 2, substitutions of a food or beverage within the same food subgroup resulted in a marked improvement in the PANDiet score (Delta = +26.4 +/- 0.2) with no significant change in energy intake. In this second scenario, the improvement in nutrient adequacy was due to substitutions in many subgroups, with no single subgroup contributing >8% to the increase in the PANDiet score. In scenario 3, substitutions of a food or beverage within the same food group resulted in the greatest improvement in the PANDiet score (Delta = +31.8 +/- 0.2) but with an increase in energy intake (Delta = +204 +/- 9 kcal/d). In this third scenario, the improvement in nutrient adequacy was largely due to substitutions of fish for meat and processed meat (similar to 30% of the increase in the PANDiet score). This study shows that a strategy based on simple substitutions within food subgroups is effective in rapidly improving the nutritional adequacy of the diet of French adults and could be used in public health nutrition actions.