The now-omnivorous dog is descended from a carnivorous species, but has since evolved to metabolize carbohydrates, fat, and fiber and remain healthy on a diet lower in protein. Could they give up on meat even more? With over 500 million pet dogs in the world, it’s a significant question. And it’s certainly not one dog owners should take lightly.
A previous 2023 review found no detrimental effect of a vegan diet in dogs, let alone a vegetarian one, though the researchers noted that studies tend to have a small sample size. Now, a groundbreaking study from the University of Nottingham has more data to paint a nuanced view.
The comprehensive nutritional study found that no plant-based diet fulfills all the nutritional requirements of dogs, though some do come very close. But here’s the kicker: neither did meat-based diets. In fact, plant-based diets were very similar to the meat-based ones.
Why is This Even a Question?
Reducing meat consumption is one of the most sustainable decisions you can take. We tend to think about using biking or using public transit, but even giving up meat once in a while could have a significant positive impact. There’s also the ethical component of not wanting animals to suffer and be killed for our consumption.
The half a billion dogs we keep as pets are also a part of that problem. As plant-based diets become increasingly common, many dog owners are wondering if they can also feed their pets plant-based food. The market has, of course, adapted. There are plenty of plant-based alternatives you can opt for. Yet, this new market is a nutritional wild west, and owners are understandably very concerned. Are these diets actually healthy?
The new study acquired 31 different brands of complete dry dog foods from UK supermarkets. They divided them into three groups:
- 19 standard meat-based foods (based on poultry, lamb, and beef);
- 6 plant-based foods;
- 6 specialized veterinary diets designed for dogs with kidney or urinary problems.
The researchers then analyzed these foods in the lab to measure their content of proteins, amino acids, fats, minerals, and vitamins. They then compared the findings to the benchmarks set by the European Pet Food Industry Federation to see how they fare.
Plant vs Meat
The study has good news for dogs on a plant-based diet. Researchers assumed these foods would be nutritionally inferior to their meat-based counterparts, particularly when it comes to protein. That didn’t turn out to be the case.
The protein analysis in plant-based foods was basically identical to that in meat-based foods. Furthermore, the quality of the protein also held up. Proteins are made of building blocks called amino acids, and not all amino acids are the same. Ten of these are considered “essential” for dogs, meaning their bodies can’t produce them and they must be obtained from the diet. Many critics of plant-based foods say these diets can’t provide the full profile of essential amino acids, but that’s not what the study found.
Four out of the six plant-based foods met all the requirements. In fact, the average concentration of high-quality amino acids was actually higher than in many of the meat-based diets. The results suggest that plant-based diets can, in fact, deliver the protein that dogs need.
But the victory wasn’t total. Just as human vegans must be mindful of certain nutrients, so too must the makers of vegan dog food. The study uncovered two consistent weak spots in the plant-based formulas: iodine and B vitamins.
Just one out of the six plant-based foods had enough iodine in it. This mirrors well-documented challenges in human plant-based diets. Similar results were found for vitamin B12, which is virtually absent in plants and plays an important role in nerve function and the formation of blood cells. But overall, B-vitamin compliance was poor across the board.
The good news is that these aren’t insurmountable problems. The researchers note that these deficiencies “could easily be supplemented.” Your dog can eat a plant-based diet, and with some minor supplements, he can be perfectly fine. Tellingly, the only plant-based food that contained adequate iodine listed seaweed and dried algae — both potent natural sources of the mineral — as key ingredients. It’s a clear roadmap for manufacturers: with thoughtful formulation and targeted supplementation, a plant-based diet can be fully complete.
The Surprising Problem
While the plant-based results offered a mix of good news and clear warnings, the study’s most alarming discovery came from an entirely different corner of the pet food world: the specialized diets vets prescribe for sick dogs.
Canine kidney disease can be a devastating diagnosis. As the kidneys fail, they struggle to filter waste products from the blood, particularly those generated from protein metabolism. For this reason, veterinarians often prescribe “renal diets,” which are purposely formulated to be low in protein and phosphorus to reduce the kidneys’ workload. These foods are labeled as “complete,” guaranteeing they provide all the necessary nutrients despite their reduced protein content.
Yet again, that’s not what the study found.
A striking 66% of the veterinary renal diets were deficient in one or more essential amino acids. Four of the six special foods failed to meet the minimum guidelines. One diet, designed to help a sick animal, was actually below the minimum for six different essential amino acids — the very building blocks of life. The most common deficiency was in threonine, an amino acid crucial for gut health and immune function.
This finding is deeply troubling. Essential amino acids are, by definition, essential. Feeding a diet that is chronically deficient in them to an already sick dog is a recipe for disaster. The researchers warn that such a diet could exacerbate existing health problems or even create new ones. A dog owner, following their vet’s advice and paying a premium for a prescription diet, could be unknowingly feeding their pet food that is starving them of the fundamental components needed to repair tissues, support metabolism, and maintain life.
The study suggests that while reducing total protein is the goal of these diets, manufacturers are failing to ensure that the remaining protein is of high enough quality to provide the non-negotiable essential amino acids. The authors point out that in human medicine, patients with kidney disease on low-protein diets are often given supplements of these amino acids to prevent malnutrition. And this step seems to be missing in the formulation of these canine foods.
The Main Takeaways
In the end, the study’s broadest and perhaps most important conclusion was that no food is perfect. We can, and should, do much better. Not a single one of the 31 products tested met 100% of the guidelines for all nutrients analyzed. When the researchers tallied the final score, the report card was sobering. Only 55% met all amino acid guidelines, a dismal 24% met all B-vitamin guidelines, and a mere 16% passed for all major and trace minerals.
This doesn’t mean your dog is in immediate danger. Many of the shortfalls were minor or isolated instances unlikely to cause clinical signs of malnutrition unless fed exclusively over very long periods. But it’s not acceptable either. The data paints a clear picture of an industry that is underdelivering. The word “complete” on the bag is more of an aspiration than a guarantee.
For dog owners, the message is not to panic, but to become more critical consumers. A plant-based diet can be a perfectly healthy choice, provided the manufacturer has paid close attention to iodine and B-vitamins. For those whose dogs are on veterinary diets, it may be time to have a frank conversation with your vet about these findings and the potential need for amino acid supplementation.
