? Food calculations are confusing me-help?

I thought I understood it, but when I calculate food carb %'s, I am getting different numbers than the charts here and the discussions I see. Can I get some help clarifying this?

Manufacturers don't list carbs. So, taking available numbers, which would be weight %, for protein, fat, fiber, moisture, and ash, whatever's left is assumed to be the carbs, right? 100-(everything else)=% carbs as weight.

Things listed after the basics, like breaking it down to omega3oils and stuff don't count, since they would be included in the crude fats, crude protein, etc, right?

Take out the water, and that's how much actual foodstuff is there. What I would call "% solids". So, to compare, for example, how much protein is in a canned food to a dry food (yes, dry is evil, but this is for understanding), you would recalculate percentages based on the adjusted dry weight.

But the best way is to compare it as calorie values, the % calories of protein, fats, and carbs. To do that, you multiply by the number of calories per gram of each, 4 for protein and carbs, 9 for fats (there are more precise numbers, yes?) and then do your percentages of total calories for each category.

Have I made any mistakes in my assumptions? If not, then how come I get much higher numbers for the Fancy Feast classic pate's than are on the official chart here and that people talk about? Here's a screenshot of a couple that I did.



where am I going wrong?

 

Hi, for pet foods a modified Atwater formula is generally used. So, protein and carbs are x 3.5, and fat is x 8.5.

Even so there are different ways of comparing the carb values of pet foods...
Some just use the calories from carbs per 100g of food for example (so of course you'll get very different values for wet and dry foods). But here (and I think on Catinfo.org) we compare by 'percentage of calories' from carbs.
To get that you divide the calories from carbs per 100g by the total calories per 100g, and then multiply by 100.

When calculating percentages of calories from carbs it shouldn't make any difference whether you use wet or dry values. To illustrate, let's say you have a dry food that has 30% of its calories from carbs. You add some water and mix it into a soupy mush. The percentage of calories from carbs in that food is still 30%, because the water doesn't affect the distribution of calories.

I'm not sure if I've explained that well... Have only had my first cup of coffee of the day, haha!

Eliz

 

That's what I'm doing. But I come up with much higher % carbs for the Fancy Feast canned foods than are listed in the master chart.
Here's the same chart as above, but with the 3.5 and 8.5 kcal multipliers instead of 4 and 9, and an expanded value (added the decimal) for the % carbs for better accuracy:


Label % carbs is calculated by subtracting the other components from 100.
% solids is adding up the protein, fats, fiber, ash, carbs.
As # Calories is the Label % (ingredient) multiplied by 3.5 for protein and carbs, 8.5 for fats. This would be the calories per 100g.
Cal/100g is the addition of calories for protein, fat, carbs.
As % Calories is the As # Calories divided by the Cal/100g, then multiplied by 100 to express it as a percentage.

So why are my calculated % calories from carbs coming out higher?

 

Are you using the guaranteed analysis values to do the calculation? If so the you calculations will be different since the guaranteed analysis values are min and max values. Dr Pearson's table is based on information obtained from the various food manufacturers of actual measured values in the food.

 

Aha.... Yes indeed, as Larry says above, if your label values are in 'guaranteed analysis' you'll need to contact the manufacturer for the current as-fed values.

Eliz