Lori,
Of the top of my head.....I don't buy it. First off Guaranteed Analysis is worthless. It doesn't tell you anything, just what the minimum or maximum percentage of the contents is. It is NOT exact.
I trust Janet and Binky's formula. I'll find a site and post the explanation of why GA means nothing.
(I think it all comes down to "they" are not saying the same thing that we are saying when it comes to carbs.... It may be a case of both formulas are "right", but their formula doesn't work in FDMB language....details below.)
Plus, they contradict themselves. First they say:
as these are true numbers for each flavor, while the Guaranteed Analysis numbers are averages.
And then they say:
This is an easy formula, and once you've done it a few times, you will be able to look at the GA and pretty much know what the carb content is based on the values given.
In the first statement they say GA is not reliable because it's just an average. Then they tell you to take that unreliable number and you'll "pretty much know what the carb content is"??? I think it's as accurate as pin the tail on the donkey if that's the "exactness".
This is from J & B's site, so you know where she got her numbers.
Numbers based on "as fed" or "actual" analysis, not "guaranteed" analysis, supplied by the manufacturers.
This is what is missing from their calculations as far as I can tell:
Assumptions: Protein and carbohydrates contain 3.5 kcals per gram, and fat contains 8.5 kcals per gram.
Here is Janet's formula, which is not the same as theirs. They don't mention that I can see, anything about percentage of
calories from carbs. Just a carb percentage, which is not the same thing. Her's is all about calories, and fat, protein and carbs have different values as far as calories per gram of food.
They aren't comparing apples to apples.
Q. How do you calculate the numbers on the table?
A. The numbers on the table are expressed as "percent of calories" (protein, fat, carbohydrate) or "amount per 100 calories" (fiber, phosphorus), based on as-fed information provided by the manufacturer. For pet foods, I follow the usual assumption that protein and carbohydrate each contain 3.5 calories per gram, and fat contains 8.5 calories per gram. You can use this Excel spreadsheet to see how the calculations are done, or read the longer explanation:
1.) Obtain "as fed" or "dry weight" values of protein, fat, carbohydrate, fiber, and phosphorus from manufacturer. Cross check: if you also have values for water and ash, the values of protein, fat, carbohydrate, fiber, ash, and water should add up to 100%. None of them should be negative.
2.) Calculate the amount of protein, etc, in 100 grams of food by dropping the percent sign. (Example: if a food is 9.5% protein, 100 grams of that food will contain 9.5 grams of protein.)
3.) Calculate total calories by multiplying protein by 3.5, fat by 8.5, and carbohydrate by 3.5, and summing the results.
4.) Calculate percent of calories from protein by dividing 3.5*protein by total calories. Calculate percent of calories from fat by dividing 8.5*fat by total calories. Calculate percent of calories from carbohydrate by dividing 3.5*carbohydrate by total calories. Cross-check: these numbers should add up to 100%, except for rounding error.
5.) Calculate grams of fiber per 100 calories by dividing fiber by total calories and multiplying by 100.
6.) Calculate mg of phosphorus per 100 calories by dividing phosphorus by total calories and multiplying by 100,000. (The extra 1000 is to change the units of phosphorus from grams to milligrams.)
More from Janet:
Q. Can I get the carbohydrate content from the numbers on the label?
A. Not in the United States of America. First of all, it's not listed on the label. Second, you can't calculate it from the label because manufacturers aren't required to put average values of protein, fat, etc. on the label. They are only required to put "guaranteed" minimum and maximum values on the label. Sometimes these values are close to what's actually in the food, and sometimes they are quite different. But in any event they are, by design, inaccurate.
If you live in a country which has consumer-friendly laws on what should be on pet food labels, carbohydrate content may be listed, or you may be able to calculate it by adding the values of protein, fat, water, fiber, and ash, and subtracting that sum from 100% to get "as fed" carbohydrate. But in the USA, you're likely to get grossly inaccurate values following this method.
Q. Why aren't the numbers on your table the same as what's on the label?
A. Because I chose to express the numbers on a per-calorie basis, see above, which I believe makes it easier to compare foods to each other. The values on the label are "wet weight" values -- they express the amount of each nutrient per 100 grams of food.
The example they showed, which says 11% carbs, is not the same as whatever number Janet comes up with because she's talking percentage of
calories. You could take any variety off J&B's list and come up with a different number using their formula. But it's the same food. Perhaps both numbers are "real", but it doesn't matter to "us" because when we tell somebody "less than 7% carbs" we mean less than
7% of the calories contained in the food are from carbs. When they say 11%, they aren't saying
11% of the calories.... I think the fundamental difference is that they don't weight their numbers on the fact that carb's and protein are 3.5 kcal/gram and fat is 8.5 kcal/gram?
Does that help any?
Carl
