The guaranteed analysis is required to give only the minimum content of protein and fat in the food and the maximum content of fiber and moisture. Other nutrients may also be listed but are not required. Having the minimum or maximum level of a nutrient will not provide all the information you need (for example, a minimum fat level of 3% listed on the label does not tell you exactly how much fat the diet contains (it might contain 3% but it usually contains more).
Another issue that commonly confuses pet owners is that the nutrient levels in the guaranteed analysis are listed on an "as fed" basis, which includes the water in the food (therefore, the protein level of a dry food will appear to be much higher than the protein level in a canned food, even if the levels are exactly the same). To compare diets to one another, you must change the numbers to a "dry matter" basis (content of the nutrients without any water).
If you want the exact nutrient content or information on nutrients not listed, call the manufacturer whose name and address must be listed on the label. The contact information for the manufacturer is one of the most useful pieces of information on the label. A company should be able to provide any other nutritional information that you might require.
If a company cannot or will not provide you with a piece of nutritional information, I would consider that to be a red flag and would not recommend that food!
Next Section: Ingredients