|
By Steve Brown and Beth Taylor
Pet food regulations do not allow the word carbohydrate on the
label. Human foods are required to list carbohydrates on the label,
however. This major difference makes it difficult to evaluate foods
for dogs and cats. That’s why concerned shoppers must do the
calculations for themselves.
Fortunately, pet food labels provide the information you need to
do them. These calculations are useful for both dog and cat foods
(for this article, the examples we use are for dog foods).
To evaluate the analysis panel of dry, canned and frozen foods,
we suggest using the simple formulas that follow. Once you understand
how they really compare to the natural diet of dogs, you’ll
be able to accurately select the best food for your pet.
The biggest building blocks of dog and cat foods (the macronutrient
content) are protein, fat, moisture and carbohydrate. Their total
must equal 100 percent.
How
the FDA defines how to calculate carbohydrates: Subtract the
weight of crude protein, total fat, moisture and ash from the total
weight (“wet weight”) of the sample of food.
The Ash Content
Ash is sometimes listed, usually for cat foods (some conventional
veterinarians believe ash is a factor in urinary tract disease).
Ash is what remains after the food is burned. It consists primarily
of elements, including calcium, phosphorous, iron, zinc and selenium.
Typically, ash content is in the 5 percent to 8 percent range, on
a dry-matter basis.
A Guaranteed Analysis of pet food is required information
on the labels of treats and foods. Here’s an example of the
typical adult dry food:
- Minimum percentage of crude protein: 26 percent
- Minimum percentage of crude fat: 15 percent
- Maximum percentage of crude fiber: 4 percent
- Maximum percentage of moisture: 10 percent
These numbers tell you the percentages by weight of the macronutrients.
In 100 grams of this food, there are 26 grams of protein (minimum),
15 grams of fat (minimum), 4 grams of fiber (maximum), and 10 grams
of moisture (maximum). Because fiber is considered a carbohydrate,
don’t subtract the fiber when you do your calculating.
These listed figures are a good estimate because most manufacturers
keep the protein, fat and moisture levels close to the listed amount.
Protein and fat look good on the label, and water adds free weight
for the manufacturer.
Here’s a formula to calculate carbohydrate percentage on
an “as fed” basis: 100 – protein – fat –
moisture – ash = Carbohydrate. Using the Guaranteed Analysis
example (100 – 26 – 15 – 10 –
6), this typical dry dog food is about 43 percent carbohydrate by
weight.
Comparing Canned and Fresh Foods
The label of a typical wet food states:
- Minimum protein: 10 percent
- Minimum fat: 8 percent
- Maximum moisture: 75 percent
- Maximum fiber: 3 percent
To compare dry and wet foods, you must remove the water from the
food. What remains is the dry matter (DM): Protein, fat, carbohydrate
and ash. A dry matter analysis tells us the percentage of DM that
is protein, fat and carbohydrate. The following is a three-step
process to calculate carbohydrate percentages on a dry matter basis:
Step 1. Calculate the total dry matter in the food. Subtract the
percentage moisture from 100 percent. If a food is 75 percent moisture,
it is 25 percent dry matter (100 – 75).
Step 2: Divide the listed macronutrient percentage by the dry matter
percentage.
Protein = Divide 10 percent by 25 percent = 40 percent protein
Fat = Divide 8 percent by 25 percent = 32 percent fat
Step 3: Use formula 1 above and calculate carbohydrates (remember
to subtract the ash)
Carbohydrates = 100 percent – 40 percent (protein) –
32 percent (fat) – 6 percent (ash) = 22 percent
Comparing Dry Food With Canned, Fresh
Foods
With these results, now it’s possible to compare the macronutrient
content of dry and canned foods. Chart 1 compares these foods on
a dry matter basis.
A better picture of the overall balance of the diet emerges when
the actual percentage of calories from each nutrient is known. Fat
provides 8-9 kcal per gram, more than twice as much as carbohydrates
and protein, which provide 3.5-4 kcal/gram, depending on the quality
of the food.
Chart 2 compares the percentage of energy provided by protein,
fat and carbohydrate for five different foods: Typical dry food,
canned, frozen, natural diet
and senior dry food. (To calculate percentage of calories provided,
first subtract the percentage fiber figure from the carbohydrate,
since fiber provides no kcal.)
Chart 2 clearly shows the striking difference between the profile
of the natural diet of the dog, and dry or senior foods. Premium
canned and frozen foods provide a more natural macronutrient content,
with fat providing about 50 percent of the calories.
Choosing foods becomes much easier when you know what the balance
of the animal’s natural diet really is! We think almost all
dogs and cats will feel much better eating diets very close to that
natural balance.
For more details on this topic and other label-reading skills,
read our book See Spot
Live Longer.
May your Spot live a long, healthy life!
| 