Plant-based diets for pets have attracted growing attention in recent years, but one question often comes up first: can dogs and cats actually digest plant-derived ingredients effectively?
Dogs and cats have different nutritional characteristics, and the scientific evidence available for the two species is far from equal. A recent review published in Animals, titled "The Digestibility of Vegan and Vegetarian Diets for Dogs and Cats", examined existing research on the digestibility of vegan and vegetarian diets and plant-based protein sources in dogs and cats.
Figure 1. The Digestibility of Vegan and Vegetarian Diets for Dogs and Cats. Produced by MDPI Academic Video Service (Source: https://encyclopedia.pub/video/1832).
1. A Question About Plant-Based Diets
The review focuses on a specific part of pet nutrition: digestibility—how effectively nutrients from food are digested and absorbed.
The authors searched Web of Science and Scopus for relevant studies published from 2000 onward. After screening the literature and reviewing references, 31 studies met the inclusion criteria. Of these, 22 focused on dogs, two on cats, and seven on both species.
This distribution is important: the evidence base is considerably larger for dogs than for cats.
2. Dogs Provide Most of the Evidence
Across the studies reviewed, digestibility values for vegan and vegetarian diets were generally high and broadly comparable with those reported for conventional meat-based diets.
Five studies specifically measured apparent total tract digestibility (ATTD) of complete vegan or vegetarian pet diets. Across these studies, ATTD values exceeded 80% for dry matter, 85% for organic matter, 80% for crude protein, 89% for fat, 88% for nitrogen-free extract, and 86% for energy.
Individual results varied with diet composition, ingredients, processing methods, and experimental conditions.
For example, one study comparing a vegetarian diet with a meat-based diet in six beagles reported ATTD above 85% for organic matter, 80% for crude protein, 93% for fat, and 88% for nitrogen-free extract.
Another study involving 61 healthy adult companion dogs compared a commercial extruded chicken-based diet with an extruded vegan diet. Crude protein digestibility in the vegan products ranged from 91.6% to 94.2%, compared with 91.7–91.8% for the animal-based product.
Together, these findings indicate that dogs can effectively digest a range of appropriately formulated and processed plant-based diets.
3. The Protein Source Matters
The review also shows why it is difficult to treat “plant protein” as a single category.
The studies examined protein sources from legumes, pulses, grains, and microbial fermentation. Their digestibility varied, and processing could also affect how nutrients become available during digestion.
Soy-derived ingredients provide one example. Different soy products showed differences in the digestibility of essential amino acids, while processing can reduce or inactivate some antinutritional factors.
For commercial pet food, this means that nutritional performance depends not simply on whether protein comes from plants, but also on the specific ingredient, how it is processed, and how it is used in the finished diet.
4. Cats Are Still Less Studied
The evidence for cats is much smaller. Only two of the 31 studies were specific to cats, although seven additional studies included both dogs and cats.
The available research nevertheless provides evidence that cats can digest a number of plant-derived protein sources. One study involving 296 cats found that true total tract protein digestibility increased as the proportion of dietary protein supplied by plant sources increased. Other studies examined plant-derived ingredients and complete diets and also reported relatively high digestibility.
These results are useful, but the limited feline evidence means that conclusions about cats need to remain more cautious than those about dogs.
5. Digestibility Is Only Part of the Story
High digestibility does not automatically mean that a diet is nutritionally complete or appropriate for every animal.
Dogs and cats require specific nutrients in appropriate amounts and proportions, and their nutritional needs vary according to species, life stage, and health status. The review therefore focuses on digestibility rather than claiming that every vegan or vegetarian diet is suitable for every dog or cat.
The authors conclude that the available evidence supports the digestibility of nutritionally sound vegan and vegetarian pet diets. Proper formulation and manufacturing remain essential.
6. What the Studies Really Tell Us
Taken together, the 31 studies challenge the idea that dogs and cats are inherently unable to digest plant-derived proteins.
Vegan and vegetarian diets generally showed high digestibility, and a range of plant-based protein sources could be effectively digested. At the same time, individual ingredients and nutrients sometimes produced different results, and the evidence is much stronger for dogs than for cats.
The findings therefore support a more specific conclusion: plant-derived ingredients can be effectively digested by dogs and cats, but digestibility alone does not determine whether a particular diet is appropriate.
7. What Remains to Be Explored
Most of the available research involves adult animals receiving maintenance diets. Much less is known about puppies, kittens, senior animals, or pets with health conditions. Many studies were also conducted under controlled conditions, making further research in everyday, in-home settings valuable, particularly for cats.
For now, the review provides a clearer picture of one part of the plant-based pet food debate. The available evidence does not indicate that nutritionally sound vegan and vegetarian diets are inherently less digestible than conventional meat-based diets—but there is still more to learn about how these diets perform across different animals and circumstances.