What Are Atwater Values and How Do We Use Them?
Learn why we use standard Atwater factors to calculate energy in homemade dog food, and how this differs from the modified values used in commercial pet food.
What Are Atwater Values?
Atwater values are the standard factors used to calculate metabolizable energy (calories) from the macronutrients in food. Named after **Wilbur Olin Atwater**, a 19th-century American chemist who pioneered the science of food energy measurement, these factors tell us how many kilocalories (kcal) of energy can be extracted from each gram of protein, fat, and carbohydrate. When you look at any food label—whether for humans or pets—the calorie count is calculated using these fundamental values. They account for: - The gross energy contained in each nutrient - Losses through digestion (what the body cannot absorb) - Metabolic losses (energy used during digestion itself) Understanding Atwater values is essential for accurately calculating how much food your dog needs, because the energy content directly determines portion sizes.
The Standard Atwater Factors
These are the values used in human nutrition and for highly digestible foods: | Nutrient | Energy per gram | |----------|----------------| | **Protein** | 4.0 kcal/g | | **Fat** | 9.0 kcal/g | | **Carbohydrate** | 4.0 kcal/g | These factors assume approximately **85-95% digestibility**—meaning most of the nutrients are absorbed by the body.
Why We Use 'Human' Atwater Values
When you prepare food for your dog using fresh, whole ingredients, you're providing nutrition that's remarkably similar in digestibility to human food. This is why we use the **standard Atwater factors**—the same values used in human nutrition. Fresh chicken, beef, eggs, vegetables, and other whole foods are easily broken down and absorbed by your dog's digestive system. Studies consistently show that fresh, home-prepared diets achieve **85-95% digestibility**, meaning your dog absorbs the vast majority of the nutrients you provide. The **National Research Council (NRC)**, the gold standard for pet nutrition research, specifically recommends using standard Atwater factors (4.0, 9.0, 4.0 kcal/g) when calculating energy content for home-prepared pet food. This recommendation exists because: - Fresh ingredients maintain their natural structure - Gentle home cooking preserves nutrient bioavailability - Minimal processing means nutrients are more accessible - The food closely resembles the human diet these values were developed for
Modified Atwater Values in Commercial Pet Food
If you've ever looked at commercial pet food calculations or nutrient profiles, you might notice different energy values being used. That's because the pet food industry typically uses **Modified Atwater values**: | Nutrient | Modified Value | |----------|---------------| | Protein | 3.5 kcal/g | | Fat | 8.5 kcal/g | | Carbohydrate | 3.5 kcal/g | These lower values exist for a good reason: **processed kibble has lower digestibility** than fresh food. During extrusion manufacturing, ingredients are subjected to: - **High temperatures** (100-180°C / 212-356°F) - **High pressure** - **Rapid processing** This process, while necessary for shelf stability and food safety in commercial products, reduces the bioavailability of some nutrients. Kibble typically achieves **70-80% digestibility**—meaning more nutrients pass through unabsorbed. The modified Atwater factors compensate for this by assuming less energy is extracted from each gram of food. This ensures commercial pet food labels provide accurate calorie counts for their specific products.
What This Means for Your Dog
When you prepare homemade food, your dog extracts **more energy** from each gram of food compared to kibble. This has practical implications: - **Portion sizes may appear smaller** than kibble portions for the same calorie intake - Your dog gets **more nutrition per gram** of food consumed - Fresh food is often **more satisfying** due to higher nutrient absorption - You may see differences in **stool volume**—less undigested waste means smaller stools We calculate your dog's serving sizes using the standard Atwater factors to ensure accurate energy intake from fresh, homemade meals.
The Science Behind Digestibility
**Digestibility** refers to the percentage of nutrients actually absorbed by your dog's body versus what passes through undigested. It's one of the most important factors in pet nutrition, yet it's often overlooked. ### Why Fresh Food Has Higher Digestibility Fresh, minimally processed foods maintain their natural cellular structure, making nutrients more accessible to digestive enzymes. When you cook at home using gentle heat, you preserve more of this nutritional value than industrial processing methods. Research consistently shows: - **Fresh meat proteins**: 90-95% digestible - **Fresh vegetables** (properly cooked): 85-95% digestible - **Commercial kibble proteins**: 70-85% digestible ### The 10-20% Difference Studies comparing fresh diets to processed alternatives typically find fresh food has **10-20% higher digestibility**. This isn't a small difference—it means your dog could be absorbing significantly more nutrients from the same ingredients when prepared fresh versus processed. This higher digestibility is exactly why the NRC recommends standard Atwater factors for home-prepared diets: they accurately reflect the energy your dog actually receives.
How We Apply This
All recipes in Aylas Kitchen are formulated using the **NRC-recommended standard Atwater factors**: - Energy calculations follow **FEDIAF and NRC guidelines** for home-prepared diets - Our serving size calculator uses these values along with your dog's metabolic weight and life stage - Nutrient profiles are calculated assuming the high digestibility of fresh ingredients **Related articles:** - [What is Metabolic Weight?](/education/what-is-metabolic-weight) - [Understanding Daily Energy Requirement](/education/daily-energy-requirement) - [Activity Factor Explained](/education/activity-factor-explained)