The French West Indies are facing increasing rates of obesity and diet-related chronic diseases. Food prices are more than 30% higher compared with mainland France, while a large part of the population is socioeconomically disadvantaged. The affordability of a healthy diet is a key issue.To identify dietary shifts allowing to achieve nutritional adequacy while reducing the cost of Guadeloupean and Martinican adult diets.Dietary intakes of 1112 adults (≥ 16y) were obtained from a cross-sectional survey conducted on a representative sample of the Guadeloupean and Martinican populations. Diet cost was based on mean prices of 1357 foods compiled from a Martinican supermarket website. Individual optimized diets respecting all nutritional recommendations with minimized departure from the initial diet were designed under different scenarios of cost constraint: none, not exceeding the initial diet cost (COSTinit), and 10%-step reductions (COST-X%); the initial diet cost referring to the cost of the diet based on initial dietary intakes and mean food prices.Without cost constraint, achieving nutritional adequacy while departing the least from initial diet increased diet cost on average (+ 20%) and for 74% of adults. In COSTinit, achieving nutritional adequacy was possible for 98% of adults and induced an increase in the amount of fruit & vegetables, unrefined starches, dairy products (especially milk), eggs and vegetable fats, and a decrease in sweetened beverages (especially among < 30y), refined cereals, sweetened products, meat and fish. In COST-30% scenario, achieving nutritional adequacy was possible for 93% of adults and induced the same dietary shifts as in COSTinit, but modified their magnitude, notably a smaller increase of vegetables (increase of + 7 g/d in the COST-30% scenario and + 86 g/d in the COSTinit scenario, both relative to initial diet), a larger increase of dairy (+ 90 g/d and + 72 g/d, respectively) and starchy foods (+ 112 g/d and + 54 g/d), and a larger reduction of meat (-48 g/d and -12 g/d). Increases in fruits (~ + 80 g/d) and unrefined starches (+ 127 g/d), and decreases in sweetened beverages (~ -100 g/d) and fish (~ -40 g/d) were maintained.Nutrition prevention programs promoting the affordable and nutritious dietary shifts identified in the present study, i.e. reduction in animal flesh foods (meat, fish) as well as refined cereals and sweet products in favour of an increase in healthy plant-based foods and animal co-products (dairy, eggs), could help improve nutritional adequacy of the Guadeloupean and Martinican populations.