Plant-Based Food for Dogs and Cats

Food production for human consumption that is high in nutritional value, low in water and energy consumption, highly sustainable, and has a reduced carbon footprint is guiding research in this field. The use of food through chemical, physical, and enzymatic processes, for example, aims to reduce waste. At the same time, the coexistence of dogs, cats, and humans has been a constant throughout human history to the point that these animals have become the world's primary interspecies companions, serving roles in protection, work, pest control, and, above all, deep emotional bonding within society.

Today, the global population of dogs and cats is estimated at between 2 and 2.5 billion animals, of which approximately 1 to 1.5 billion live in households and depend on human care. The fact that these animals are carnivores is a challenge, since they are potential competitors with humans for the planet's food resources. At present, this competition is not readily apparent because the industrial production of pet food relies primarily on ingredients that are not used for human consumption, ranging from agricultural residues to animal by-products, positioning pets at the final stage of the agricultural value chain while generating additional income for producers of these raw materials.

This raises an important question: if a paradigm shift were to occur—for example, a reduction in food production with a high carbon footprint and high-water consumption, such as animal-derived products, alongside a transition toward more sustainable production systems based on plant-based foods, algae, insects, and other alternatives—would it still be possible to sustain the current population of carnivores living alongside humans?

In the context of global sustainability, the social and environmental impact of pet food has become strategically important, particularly because pet food relies on animal-derived ingredients (Pedrinelli et al., 2021, 2022). Considering that food production for human consumption already places significant pressure on natural resources, companion animal nutrition adds another complexity to the scenario. Every year, the global food system accounts for 34% of total anthropogenic greenhouse gas (GHG) emissions and is also the primary driver of ocean eutrophication (approximately 78%) and freshwater eutrophication (approximately 95%). In 2013, the Food and Agriculture Organization of the United Nations (FAO) estimated that the livestock sector accounted for 14.5% of global GHG emissions. More recent data indicate that the production of animal-derived foods, which forms the foundation of the pet food industry, is responsible for at least 20% of global anthropogenic emissions.

Within this context of growing concern over global sustainability, the carbon pawprint concept has emerged, adapting the idea of ecological footprint to measure the impact of resource consumption (land, water, and energy) associated with companion animals. Given the enormous global population of dogs and cats, the environmental impact of feeding them is substantial (Knight et al., 2022). Consequently, there is broad consensus that the impact of companion animal nutrition is significant and should be considered within climate change mitigation strategies.

This is not merely an ideological issue, nor is it an attempt to turn carnivores into herbivores. Rather, the question is whether it would be possible to maintain today's companion animal population in a healthy and sustainable manner if animal-derived food resources became less available. Answering this question requires evaluating multiple factors regarding carnivore metabolism and physiology, current and future food sources, the impact of today's carnivore population on sustainability goals, and other relevant considerations.

The Order Carnivora includes thousands of species with very different characteristics. For example, although taxonomy is primarily based on anatomy (anatomical carnivores), feeding behavior in the wild (preferential carnivores), metabolism, and other traits also define different family groups. Thus, although giant pandas (Ailuropoda melanoleuca) are anatomical carnivores, their feeding preferences and habits enable them to thrive on strictly plant-based diets. Dogs (Canis lupus), on the other hand, because of the enormous genetic variability resulting from human intervention and/or geographic isolation, may be classified as "preferential carnivores," "facultative carnivores," or even "opportunistic carnivores." This means they will always prefer meat, but in its absence, they can maintain their health by consuming plant foods naturally available in the environment, such as fruits, leaves, and roots. According to Axelsson et al. (2013), the 52 dog breeds evaluated in a genomic study showed considerable variation in their ability to digest starch. However, all of them possessed significantly more copies of genes associated with starch digestion (from 6 to 24 copies) than the 12 wolf populations included in the study. In contrast to wolves' carnivorous diet, the adaptation to a starch-rich diet represented a crucial step in the domestication of dogs.

Domestic cats (Felis catus), by contrast, retain strong metabolic similarities to their wild ancestors. Over millions of years, they developed metabolic adaptations that enabled them to maximize the utilization of prey composed primarily of protein and fat while suppressing the production of enzymes such as amylase, whose synthesis represented an unnecessary metabolic cost. These adaptations characterize cats as "obligate carnivores" or "metabolic carnivores," meaning that under natural conditions they depend on nutrients found exclusively in animal-derived foods, including arachidonic acid and taurine.

On the other hand, it is well established that pet diets can be formulated and produced using plant-derived ingredients, provided that the necessary nutritional adjustments are made to correct existing nutrient deficiencies and excesses. Understanding the nutrients that make up a plant-based diet is essential for evaluating its applicability in dog and cat nutrition. Although the nutritional requirements of these animals can be met using plant-derived ingredients, formulation requires a careful approach to ensure nutritional adequacy, bioavailability, and an appropriate balance among nutrients (Roberts et al., 2023).

Contemporary scientific literature demonstrates significant growth in both the market for and interest in plant-based dog foods, driven by vegan pet owners who wish to align their personal values with the diets they feed their animals. At the same time, sustainability has become a central pillar of this discussion. Strong evidence indicates that transitioning to nutritionally complete plant-based diets offers important environmental benefits, including substantial reductions in land use, water consumption, and greenhouse gas emissions compared with diets based on animal-derived ingredients.

Finally, plant-based diets for dogs and cats have remained a controversial topic regarding concerns about their nutritional adequacy for carnivorous animals. However, the growing body of scientific evidence suggests that properly formulated vegan diets can be nutritionally complete. In addition to the theoretical evaluation of nutrients and food composition, it is essential to evaluate the long-term health effects of these diets in dogs.

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References
KNIGHT, A. et al. Vegan versus meat-based dog food: Guardian-reported indicators of health. PLoS ONE, v. 17, n. 4 April, 1 abr. 2022. 
KNIGHT, A. The relative benefits for environmental sustainability of vegan diets for dogs, cats and people. PLoS ONE, v. 18, n. 10 October, 1 out. 2023. 
KNIGHT, A.; LEITSBERGER, M. Vegetarian versus meat-based diets for companion animals. Animals, 2016. 
KNIGHT, A.; SATCHELL, L. Vegan versus meat-based pet foods: Ownerreported palatability behaviours and implications for canine and feline welfare. PLoS ONE, v. 16, n. 6 June 2021, 2021. 
KNIGHT, A.; SATCHELL, L. Erratum: Vegan versus meat-based pet foods: Owner-reported palatability behaviours and implications for canine and feline welfare (PLoS ONE (2021) 16: 6 (e0253292) DOI: 10.1371/journal.pone.0253292). PLoS ONEPublic Library of Science, 2021.