How should pet parents calculate macronutrients?

Understanding the composition of diets helps pet parents determine the primary energy source - Canine nutrition researcher and professional sled dog racer, Dr. Mark Roberts, Ph.D., explains how to calculate macronutrients— and how a low-carb diet for dogs can help.

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KEY TAKEAWAYS:

  • The "as fed" basis on food labels includes moisture content, which can limit comparison accuracy. Converting to dry matter basis offers a clearer comparison.

  • Metabolizable Energy (ME) measures the energy available from each macronutrient in a diet. Fat provides more energy per gram than protein and carbohydrates.

  • The dry matter basis approach is aligned with AAFCO's nutrient profile standards, ensuring a reliable assessment of a diet’s completeness and balance.

Introduction

Looking at the contribution each macronutrient (i.e. protein, fat, carbohydrates) makes to a diet is something pet parents should do when comparing diets. By doing so, they will facilitate an understanding of whether a dog, for example, is relying primarily on carbohydrates or fat as its main energy source. Additionally, determining the protein content of a diet is beneficial, as its contribution can impact on factors such as muscle repair, growth, and immunity. In canine nutrition, two methods are commonly used to calculate the macronutrient composition of a diet: 1) dry matter basis, and 2) the percentage of energy derived from each macronutrient.  

What is Dry Matter Basis?

Dry matter basis can be described as an expression of nutrients with any contribution from moisture completely removed from a given diet. This is different to the guaranteed analysis information on a dog food product, which is referred to as being on an “as fed” basis. This means that the nutrients on a dog food label reflect what the food is when provided to a dog. Although helpful, this information limits the ability to compare the protein, fat, and carbohydrate content of a diet with those of varying moisture content, such as freeze-dried and canned foods (which contain significantly more water).

The advantage of converting the as-fed basis to dry matter basis is that it enables a direct comparison between products, regardless of moisture content. Another advantage of the assessing nutrients on a dry matter basis is that the American Association of Feed Control Officials (AAFCO) uses this approach in their dog food nutrient profile (1), regarding a diet being complete and balanced. Thus, a clear and direct assessment of the nutrient levels in a dog food can be performed with the nutrient profile.

Energy Sourced from each Macronutrient

Calculating the energy derived from each macronutrient is commonly referred to as metabolizable energy (ME) or simply as energy, for example, 40% protein ME or 40% protein as energy. The ME of diets can be determined through direct estimation, which consists of the difference between digestible energy from a diet and energy loss through the urine of a dog. However, because direct estimation is costly and time consuming (2), indirect estimation is more commonly applied. This involves modified Atwater factors, whereby protein and carbohydrate provide 3.5 kcals per gram and fat 8.5 kcals per gram (3). This method accounts for the determined digestibility of each macronutrient and thus the energy it provides.

Similar to dry matter basis, metabolizable energy removes any contribution moisture has to a diet; however, it also provides additional nutritional insights. Since dogs need a certain amount of energy to function, the overall contribution each macronutrient makes to this is important. For example, a diet with a higher protein content than fat on a dry matter basis might provide much lower metabolizable energy from protein compared to dietary fat, due to fat containing over double the amount of energy.

Conclusion

In summary, using the dry matter basis and metabolizable energy methods to assess different dog foods has advantages. By utilizing both, you can easily compare macronutrients with other diets, while also determining how much energy from each macronutrient a dog have access to.

References

1.    AAFCO. The AAFCO Official Publication. The Association of American Feed Control Officials, Inc.; 2024.

2.   Saldarriaga, J. D., Posada, S. L., & Trujillo, J. H. A. (2017). Assessment of energy content in dog foods. Archivos de zootecnia, 66(254), 279-286

3.   Atwater, W.O. 1910. Principles of nutrition and nutritive value of foods. Department of Agriculture. Farmer’s Bulletin. Washington, D.C. 142 pp.

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