When choosing dog food, pet owners often rely on the Association of American Feed Control Officials (AAFCO) statement on the packaging, which confirms a diet is "complete and balanced" for their dog's life stage.
This designation is meant to be a guarantee of nutritional adequacy.
What if that guarantee has a critical flaw?
A 2025 nutritional analysis conducted by researchers at the University of Nottingham and published in a peer-reviewed journal assessed 25 commercial dry dog foods. The study included 19 meat-based and 6 plant-based formulas. The finding was clear: zero of the 25 diets met all nutritional guidelines set by the European Pet Food Industry Federation (FEDIAF) and AAFCO, despite all carrying the “complete and balanced” claim.
The deficiencies were not random. The research identified two consistent patterns:
- Iodine was insufficient in 24 of the 25 foods.
- B vitamins were significantly deficient in the plant-based foods.
This indicates a potential systemic issue in pet food formulation and processing, not a problem isolated to a single brand or diet type.
This article dissects those scientific findings, explains the regulatory context behind the “complete and balanced” label, and provides a concrete, actionable plan to ensure your dog’s nutritional needs are met.
The Nottingham Study: Methodology and Findings
The University of Nottingham study provides a data-driven snapshot of the commercial dog food market. The researchers’ methodology was straightforward: they acquired 25 commercially available dry dog foods and conducted a laboratory analysis to compare their nutrient profiles against the FEDIAF and AAFCO nutritional guidelines.
The results were quantitative:
Protein and Amino Acids
All 25 foods, including the plant-based ones, contained acceptable concentrations of protein, fatty acids, and essential amino acids.
Iodine
24 out of 25 foods failed to provide sufficient iodine.
B Vitamins
The plant-based foods consistently lacked adequate levels of B vitamins, which are crucial for neurological function, skin health, and energy metabolism.
Andrew Knight, a Professor of Animal Welfare and Ethics at Murdoch University, summarized the implication: “Consumers are expecting that if products are labelled as being nutritionally sound, that will be true, but clearly it’s not true.”
Understanding the "Complete and Balanced" Label
The term “complete and balanced” is a regulatory term, not a measure of optimal quality. In the United States, the AAFCO defines the minimum nutrient requirements for dogs. Pet food manufacturers can achieve this designation through one of two methods:
1. Formulation Method
The diet is formulated to meet AAFCO nutrient profiles on paper, using standard nutrient values for each ingredient. No feeding trials are required.
2. Feeding Trial Method
Dogs are fed the diet as their sole nutrient source for a minimum of six months. The dogs must maintain body weight and show no signs of clinical deficiency.
The Nottingham study suggests that both methods can result in foods that meet the minimum legal standard while still lacking certain nutrients in practice, likely due to variations in ingredient sourcing, bioavailability, or high-temperature processing that degrades sensitive nutrients.
The Two Most Common Nutritional Deficiencies
The study identified two specific and consistent nutritional gaps.
Iodine
Function
Iodine is an essential mineral required for the synthesis of thyroid hormones, which regulate metabolism, growth, and development.
Signs of Deficiency
Unexplained weight gain, lethargy, hair loss, and dull coat.
The Reason for Deficiency
Iodine content in ingredients can vary widely based on the soil they were grown in or the feed given to livestock. Formulations may not adequately account for this variability.
B Vitamins (B12, Riboflavin, etc.)
Function
B vitamins act as coenzymes in critical metabolic processes for energy production, red blood cell formation, and nervous system function.
Signs of Deficiency
Lethargy, weakness, poor coat quality, and neurological issues.
The Reason for Deficiency
B vitamins are water-soluble and sensitive to heat. The high-temperature extrusion process used to create kibble can destroy them. Plant-based ingredients are also naturally lower in several B vitamins.
A Realistic Guide to Evaluating Commercial Dog Food
Given these findings, consumers must look beyond the marketing claims on the bag.
Questions to Ask a Pet Food Company:
“Is your ‘complete and balanced’ status based on formulation or a feeding trial?”
“Do you conduct post-production testing on finished batches of food to verify nutrient levels, particularly for iodine and B vitamins?”
“Do you employ a full-time board-certified veterinary nutritionist (DACVN) on your formulation team?”
Tangible Signs of a Higher Standard:
The company publicly shares the calorie content (kCal per cup) on its packaging.
The company clearly discloses its manufacturing location and quality control processes.
The product has an NASC (National Animal Supplement Council) quality seal if it includes supplemental nutrients.
How to Address Potential Nutritional Gaps
Consult your veterinarian before making any changes to your dog’s diet. The following plan should be discussed with them.
1. Audit Your Current Food
Locate the AAFCO statement on the bag. Note whether it is based on formulation or feeding trials.
2. Contact the Manufacturer
Email the company. Ask: “Can you provide the typical iodine and vitamin B12 content for your [Product Name] from finished product testing?”
3. Discuss Testing with Your Veterinarian
4. Consider Strategic Supplementation Under Veterinary Guidance
For Iodine
A veterinarian can recommend a specific kelp-based supplement that is tested for pollutants and heavy metals (e.g., Vetriscience Sea Thyroid or Iodine from Rx Vitamins). They will provide the exact dosage based on your dog’s weight. Iodine is toxic in excess; professional guidance is non-negotiable.
For B Vitamins
Nutritional yeast is a palatable source. A veterinarian may also recommend a specific pet-safe B-complex vitamin.
5. Monitor Your Dog
Track your dog’s energy levels, skin and coat health, and body weight. Report any changes to your veterinarian.
Navigating Plant-Based Nutrition for Dogs
The Nottingham study confirmed that well-formulated plant-based kibbles can provide adequate protein and amino acids. The deficiencies found were in micronutrients that can be supplemented.
Dogs are omnivores capable of thriving on a variety of diets. For owners seeking a plant-based diet for ethical or environmental reasons, the path is clear:
- Select a commercial plant-based food from a company that demonstrates transparency.
- Work with your veterinarian to implement the action plan above, specifically addressing iodine and B vitamin supplementation.
The Path Forward for Pet Food Standards
This study highlights an opportunity for evolution in the pet food industry. Higher standards could include:
Mandatory Post-Production Testing
Requiring finished product testing for key sensitive nutrients to verify label claims.
Longer-Term Feeding Trials
Extending trial periods to better detect subtle deficiencies.
Increased Transparency
Encouraging brands to publicly share more detailed nutrient analyses beyond minimum requirements.
As consumers, supporting companies that voluntarily adopt these practices can drive broader change.
Move from Concern to Action
Awareness is the first step. Action is the next.
Your most valuable immediate step is to gather information. Contact your dog food manufacturer. Use the question provided above. Their response will provide concrete data to discuss with your veterinarian.
How to Talk to Your Veterinarian: “I read a peer-reviewed study that found iodine deficiencies in 24 out of 25 commercial dog foods. I feed [Your Brand]. I’ve contacted the company for their finished product test data. Based on my dog’s health, would you recommend any specific blood tests or have any concerns about potential deficiencies we should address?”
This approach is collaborative, evidence-based, and focused on your individual dog’s health.
Disclaimer: This article summarizes a specific scientific publication and is for informational purposes only. It is not a substitute for professional veterinary advice, diagnosis, or treatment. Always seek the advice of your veterinarian with any questions you may have regarding your pet's health and nutrition. Never disregard professional advice or delay in seeking it because of something you have read here. The mention of any specific supplement brand is for informational illustration only and does not constitute an endorsement. All supplementation must be approved and supervised by a veterinarian.
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