What I do is take the fat grams and multiply them by 9, take the carbs and protein and multiply them by 4 then add it all together and if it equals the amount of calories listed, then there is nothing hidden, if it doesn't come out, figure up the difference between what you came up with and what they say the calories are and divide that number by 4 and the answer is how many hidden carbs there are. Try it on the foods in your fridge and you will see how it works. Tuna in spring water is exact, use that to practice the formula and you will get an understanding of it.