What 31 studies say about plant-based food for dogs

Doges Editorial · 2026-05-17 · 5 min read

A new review published in the journal Animals examined 31 studies on vegan and vegetarian diets for dogs. The conclusion challenges a common assumption: plant-based diets are consistently well-digested — broadly comparable to conventional meat-based food.

If you have ever let your dog work through a stolen broccoli stalk or watched them systematically devour the contents of the vegetable garden, you may already have a suspicion: dogs are more omnivorous than their reputation suggests. Their history, after all, is thousands of years of eating what humans left behind — which included a lot of bread, a lot of scraps, and not always a neat portion of meat.

But the official version has long been simpler: dogs need meat. Vegan and vegetarian pet food, the argument goes, might work in theory, but the dog's gut isn't built for it. A new review, published May 9 in the journal Animals by Andrew Knight of Murdoch University in Perth, Australia, took 31 studies and checked whether that argument holds up.

The question the review set out to answer

Knight's review is specifically about digestibility — how well the dog's digestive system processes and absorbs nutrients from plant-based diets. This is a narrower question than nutritional completeness (which asks whether the diet has everything a dog needs) or long-term health outcomes. Digestibility is the upstream question: can dogs even absorb what's in plant-based food?

The review included 31 studies: 22 specific to dogs, two to cats, and seven applicable to both. They covered a wide range of designs — short-term feeding trials, long-term observations, different breeds, different plant protein sources including soy, legumes, pulses, grains, and proteins produced through microbial fermentation. The question asked of each: were the nutrients in plant-based diets being absorbed?

What the numbers show

The review's findings were consistent across the breadth of those 31 studies. Vegan and vegetarian diets for dogs showed digestibility values that were high — and broadly comparable to what researchers typically find with conventional meat-based diets.

In the five studies that measured what scientists call apparent total tract digestibility (ATTD) — a standard measure of how much of a diet is actually absorbed — values exceeded 80% for dry matter, 85% for organic matter, 80% for crude protein, 89% for fat, and 86% for energy. These are not marginal numbers. They suggest that when dogs are fed a well-formulated plant-based diet, their digestive systems handle it effectively.

Digestibility values of veg*n diets were consistently high and broadly comparable to those of conventional meat-based diets.

— Andrew Knight et al., Animals (May 2026)

Why this might not surprise evolutionary biologists

Dogs diverged from wolves somewhere between 15,000 and 40,000 years ago, and the early period of that divergence almost certainly happened around human settlements — around cooking fires, refuse heaps, and the edges of agricultural fields. One genetic marker of that transition stands out: dogs have significantly more copies of the AMY2B gene than wolves do. AMY2B codes for salivary amylase, the enzyme that begins starch digestion in the mouth. Wolves barely have it. Dogs have expanded it.

That expansion is thought to have been a key adaptation to the human diet — to a world where starchy, plant-derived food was suddenly available in volume. Dogs didn't just tolerate carbohydrates. They evolved toward them.

The AMY2B story gets more specific when you look at the numbers. Wolves typically carry two copies of the gene. Domestic dogs have between four and thirty copies — and the variation tracks closely with how long their ancestors lived alongside early humans. Dogs from agricultural regions, where grain dominated the food supply for thousands of years, tend to have more copies than dogs from pastoral or nomadic populations. Evolution left a record, and it's written in their saliva.

The caveats that matter

The review is careful about what it is and isn't claiming. Digestibility — the ability to absorb nutrients — is not the same thing as nutritional completeness. A diet can be highly digestible while still being nutritionally incomplete: deficient in certain amino acids, vitamins, or minerals that a dog needs to stay healthy over time.

Knight notes that vegan and vegetarian diets for dogs need to be carefully formulated to be nutritionally sound, and that not all commercially available plant-based dog foods meet those standards. In the United States, the AAFCO (Association of American Feed Control Officials) provides nutritional guidelines that well-formulated diets should meet. Checking for AAFCO compliance on a label is the simplest first step any owner can take.

These findings support the use of nutritionally sound veg*n pet diets. Such diets are not normally significantly less digestible than conventional meat-based diets.

— Andrew Knight et al., Animals (May 2026)

What this does and doesn't tell owners

For dog owners who have been curious about plant-based diets — whether for environmental reasons, animal welfare concerns, or because their dog has developed a sensitivity to certain proteins — this review removes one of the most common objections. "Dogs can't digest plant-based protein" is not supported by 31 studies examining the question directly.

What it doesn't do is tell owners that vegan food is categorically better. Knight's review makes no such claim. Individual dogs vary, protein sources vary, and the difference between a well-formulated plant-based diet and a poorly formulated one is significant. The study's message is more modest, and probably more useful: digestibility is not the reason to say no.

The broader picture

There is a growing segment of the pet food market moving toward plant-based options — driven partly by owners who don't want their environmental footprint routed through the livestock industry, and partly by dogs who do better on novel proteins when conventional sources cause problems. This review gives that market better scientific grounding on at least one key question.

The conversation about what to feed dogs has always been tangled up with identity — what kind of owner you are, what you think a dog fundamentally is, whether carnivore is destiny or starting point. Knight's review doesn't resolve that conversation. It just clears away one piece of the argument that wasn't resting on much evidence to begin with.

Next time your dog eats a carrot from the ground on a slow morning walk, their gut will handle it just fine. That, at least, is now in the data.