What are these numbers? Nutrition Math 101
Calorie Content
Thankfully as of 2015, pet food guidelines now include calorie statements, but with a grace period for all companies to change their labels by January 2017. This means complete and balanced pet foods (but not necessarily all treats) will have calories on the back of the package by weight (kilocalories per kilogram) and volume (kilocalories per cup or can). Unless you weigh your pet’s food, kilocalories per kilogram (or kcal, which is the same as 1 Calorie just like human foods) isn’t very helpful.
Knowing the kcal per cup, however, can be helpful in deciding how calorie-dense you want your pet’s food to be. If you want your pet to have more volume of food or you’re looking to slim your pet down, aim for pet foods that are around 300 kcal per cup or less. Similarly, look for dog food that is around or under 300 kcal per large (13 oz) can or cat food under 150 kcal per medium (6 oz) can.
In order to figure out how many kcals your pets needs per day, our blog on counting calories can help guide you with a calculator: https://sites.tufts.edu/petfoodology/2016/02/how-much-should-i-feed-my-dog-or-cat/.
Guaranteed Analysis
The guaranteed analysis on pet food labels cannot be used to compare pet foods as they’re written. For example, a food with 21% minimum protein on a guaranteed analysis means that for every 100 lbs of pet food, at least 21 lbs will be protein. That’s not helpful if you have foods with different calorie content, moisture content (think can vs dry), or fiber content. Also, remember these numbers are in maximum or minimum values, so there could be more than 21% protein, that’s just the guaranteed minimum based on the label guidelines.
The good news, though, is if a food is complete and balanced with an AAFCO Statement and made by a company that meets quality control criteria (see more on this here: https://vetnutrition.tufts.edu/2016/01/important-information-you-could-be-misreading-on-the-pet-food-label/), your food has all the necessary nutrients your pet needs in the right proportions. If you still want to compare protein or fat between foods, here are the math steps to take.
- Select a nutrient you want to compare and find the guaranteed analysis percentage (common nutrients to compare include protein, fat, and fiber):
Diet A: Adult Dry Dog Food
Protein (Min): 25.0%
Diet B: Adult Canned Dog Food
Protein (Min): 8.0%
- Find the calorie density (kilocalories per kilogram) on the label:
Diet A: Adult Dry Dog Food
3,606 kcal/kg
Diet B: Adult Canned Dog Food
1,198 kcal/kg
- Do a quick calculation (divide percentage by calorie density then multiply by 1,000):
Diet A: Adult Dry Dog Food
25.0% Protein / 3,606 kcal/kg x 1,000: 6.9 grams of protein per 100 kcal
Diet B: Adult Canned Dog Food
8.0% Protein / 1,198 kcal/kg x 1,000: 6.7 grams of protein per 100 kcal
Voila! Now you can compare these two diets on the same scale.
Update August 2017: We now have a calculator that will do the math for you. Check it out!