The aim was to estimate the greenhouse gas emissions (GHGE) associated with self-selected diets and to evaluate the impact of modifying dietary structures on diet-associated GHGE. Food consumption data from 1918 adults participating in the French national dietary survey and GHGE of 73 highly consumed foods (in g CO2e/100 g of edible food) were used to estimate the GHGE of each individual diet. The mean diet-associated GHGE was 4170 g CO2e/day and a high inter-individual variability was observed. When the total caloric intakes were reduced to meet the individual energy needs, the diet-associated GHGE decreased by either 10.7% or 2.4%, depending on the assumption made on the average physical activity level of the population. The meat and deli meat food group represented the strongest diet-associated GHGE contributor, but the impact of different meat reduction scenarios was modest. In particular, when fruit and vegetables were iso-calorically substituted for meat, either null or even positive diet-associated GHGE variations were observed because the needed amounts of fruit and vegetables to maintain the caloric content of the diet were high. Therefore, substituting fruit and vegetables for meat (especially deli meat) may be desirable for health but is not necessarily the best approach to decreasing diet-associated GHGE.