You can add more cheese. For a traditional, creamy soup, use a combination of cheese and cream. To reduce the amount of fat, you can choose the mildest type of cheese and omit the butter altogether. While a traditional cream of tuna soup will be full of flavor and nutrients, a diet version will contain fewer calories and fat. If you're on a diet, you should add light cream, milk, and margarine.
This website provides approximate nutrition information for convenience and as a courtesy only. Nutrition data is gathered primarily from the Spoonacular Database, whenever available, or otherwise other online calculators.