Lipids are the most energetic macronutrients (as a reminder: 1 g of lipids represents 9 kcal, against 4 kcal for 1 g of carbohydrates or 1 g of proteins). Lipids are the molecules present in the fat of foods. They divide into saturated fatty acids and unsaturated fatty acids. These fatty acids can contain between 4 and 20 carbon molecules while carbohydrates contain between 3 and 6 carbon molecules.
