Navigating Dietary Fiber Testing in Pet Food: How to Choose the Right Method for Your Product

Introduction

The pet food industry is undergoing a significant shift, driven in part to the recent Pet Food Label Modernization (PFLM) initiative from the Association of American Feed Control Officials (AAFCO).

One of the most impactful changes: Dietary fiber is now a required component on pet food labels—replacing the outdated "crude fiber" metric in the guaranteed analysis panel.

This isn’t just a labeling technicality. It marks a fundamental step toward more accurate and meaningful nutritional data for pet owners, veterinarians, and formulators alike. But with several dietary fiber testing methods on the table—and each measuring different components—how do manufacturers choose the right one?

Here’s what you need to know about dietary fiber in pet food, how it’s tested, and how to select the best analysis method for your product or ingredient.

Why Dietary Fiber Matters 

Dietary fiber is a non-digestible carbohydrate that plays a critical role in digestive health, satiety, and microbiome support—for both humans and pets. Unlike crude fiber, which primarily quantifies the insoluble portion of fiber, dietary fiber encompasses a broader and more relevant spectrum of components. These include soluble fiber, insoluble fiber, resistant starches, and low molecular weight fibers—also known as fibers that are soluble in aqueous ethanol during analysis—more on these later.

With PFLM now requiring dietary fiber on pet food labels, accurate testing is essential to reflect the nutritional profile of both finished products and raw ingredients.

Crude Fiber vs. Dietary Fiber: A More Complete Picture

Prior to AAFCO’s adoption of PFLM in 2023, pet food products only needed to declare crude fiber on their guaranteed analysis panel. Crude fiber is determined using a method developed over a century ago and captures only a limited portion of insoluble fiber—excluding soluble fiber, resistant starches, and other low molecular weight fiber types.

AAFCO’s decision to require total dietary fiber (TDF) reflects a growing industry consensus: crude fiber is no longer nutritionally informative. As a result, labels are now evolving to reflect fiber content that more closely aligns with its actual impact on animal health.

Understanding the Main Types of Dietary Fiber

To select the right testing method, it’s essential to first understand what types of fiber your formula contains. Here’s a quick breakdown:

Choosing the Right Method for Dietary Fiber Testing in Pet Food

With dietary fiber now a required component on pet food labels under AAFCO’s Pet Food Label Modernization, selecting the correct testing method is critical. There are several laboratory methods available to quantify dietary fiber in pet food. The best choice depends on your product type, ingredient composition, and desired fiber claims.

Key Considerations for Method Selection

• Product Type: Wet, dry, raw, or baked products may behave differently during analysis.
• Ingredient Profile: Whole grains, legumes, added prebiotics, and functional fibers require comprehensive methods.
• Labeling Goals: Are you aiming to meet minimum compliance, or do you want to highlight specific health benefits?

Also consider working with a lab experienced in pet-specific matrices, as fiber measurement can vary significantly compared to human food analysis.

Common Methods for Dietary Fiber Testing

AOAC 991.43: AAFCO’s Recommended Method of Quantification

AOAC 991.43, also known as the Lee Method, is AAFCO’s recommended method for dietary fiber testing in pet foods. This enzymatic-gravimetric method has been used for many years for animal food and feed ingredients. Many considerations were factored into the decision to recommend AOAC 991.43 for dietary fiber. To simplify the thought process, the method was selected because it is appropriate for the majority of products, given the types of fibers present, and is already widely utilized. Therefore, there was less need for new method implementation at both regulatory and third-party laboratories.

The two-part method quantifies total dietary fiber as the sum of soluble and insoluble dietary fiber—or it can report the two components separately. It is designed to capture high molecular weight fibers, which are the most prevalent types in most traditional formulations.

Best for:

• Routine labeling for PFLM compliance
• Products without high levels of prebiotic or synthetic fiber additives
• Typical dry, canned, or raw pet foods using conventional ingredients like grains, vegetables, or cellulose

Other Dietary Fiber Testing Methods

While AOAC 991.43 is suitable for most products, it may not capture all fiber types present in more complex or functional formulations. Depending on your goals—especially if you’re using modern or innovative ingredients or targeting specific marketing claims—you might need a more comprehensive method.

1. AOAC 2009.01
2. AOAC 2011.25
3. AOAC 2017.16
4. AOAC 2022.01
5. Custom Testing Combinations

For a deeper dive into these testing methods, watch our on-demand webinar:

Dietary Fiber in Pet Food: Differentiating Methods and Selecting the Best Fit for your Formula.

Final Thoughts: Fiber with Purpose

As dietary fiber becomes a required element in the guaranteed analysis, pet food manufacturers are facing a new level of scrutiny—and opportunity. Selecting the right fiber testing method not only ensures compliance with AAFCO’s Pet Food Label Modernization but also allows for a more transparent, health-forward narrative for pet owners.

Whether you’re launching a new high-fiber formulation or simply updating your labels, accurate dietary fiber testing is no longer optional. It’s the new standard.

Need help selecting the right method?

Work with a lab partner experienced in dietary fiber testing for pet food today. 

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