In a 2024 study published in PLOS, the investigators enrolled 15 clinically healthy dogs from Los Angeles County households to evaluate clinical, hematological and nutritional parameters in dogs over a year. The plant-based diet included pea protein as a main ingredient.
“We tackled one of the most challenging clinical scientific questions: why attempt to fix something that isn’t broken?” said Dr. Tonatiuh Melgarejo, DVM, Phd, an author on the study. “Our goal was to demonstrate that clinically healthy dogs on a meat-based diet would remain clinically healthy after 12 months on a well-balanced vegan diet.”
Twelve months is equivalent to seven dog years.
Quarterly physical exam results combined with monthly histories reported by pet owners confirmed that the dogs remained healthy during the study.
“We measured thousands of parameters, including serum chemistry panel markers, complete blood count, urinalysis, lipid and water-soluble vitamins, plasma free amino acids, cardiac biomarkers, body weight and body condition scores—essentially everything," Melgarejo said. “Interestingly, at the end of the year, the dogs were healthier based on these parameters.”
For most of the participating dogs, vitamin D levels were insufficient at the start of the study. These levels normalized in most dogs at six months and all dogs at 12 months, achieved solely on a plant-based diet without supplementation. Melgarejo told NutraIngredients that this finding was “extraordinary and unprecedented in veterinary medicine.”
According to a study that appeared in Metabolites, “dogs and cats have differences in vitamin D metabolism compared to other mammalian species, as they are unable to perform vitamin D cutaneous synthesis through sun exposure.”
They are dependent on the dietary consumption of this nutrient.
The Western University study, which cost nearly $300,000 to conduct, may be the most expansive investigation into plant-based diets for dogs, Melgarejo said.
Netflix fame
Interest in the Western University study has reached beyond academia. A documentary short released in January on Netflix outlined the study’s findings but also ventured into the economic and environmental impact of feeding pets a meat-based diet.
According to the film in which Melgarejo appears, the amount of meat used for dogs and cats is equivalent to the meat consumption of the entirety of Italy. If pets had their own country, it would be the fifth largest meat-eating country in the world. It is estimated that 30% of the total carbon footprint for food production in the United States comes from dog and cat food.
There is a wide array of options for a vegan diet, Melgarejo said.
“During a trip to Italy, I observed many foods that are available in the United States but are not typically part of a dog’s diet,” he added. “These include amazing anti-inflammatory fruits rich in vitamins C and D. For instance, I saw dogs eating mandarins.”
There are several areas in Italy known as blue zones, a term coined by journalist Dan Buettner, a National Geographic Explorer and Fellow. After an expedition to Okinawa, Japan in 2000 to investigate longevity in the country, Buettner set out to find other regions of the world with reportedly long lifespans.
“If people in these regions are living longer, are their dogs as well?” Melgarejo said. “I have had the privilege of traveling to 46 countries, where I have observed a wide variety of diets for dogs. From Egypt to Thailand, Indonesia to Mexico, Patagonia, and various countries in Asia, the diets are remarkably diverse. In many regions, dogs primarily consume vegan diets due to the economic constraints that limit access to animal products. For instance, in Mexico, some dogs subsist on simple meals of tortillas and beans.”
