Making sustainable choices means helping conserve the planet’s limited resources. Can the way we feed our companion animals be both healthful and sustainable?

It is no secret that our planet and its inhabitants are facing a climate crisis. In August of 2021, the United Nations Intergovernmental Panel on Climate Change released its latest report, showing that human influence has warmed the atmosphere, oceans, and land to unprecedented levels over the past 2,000 years.1 As a result, we are seeing daily news reports of extreme temperatures; extended droughts, fires, storms, and flooding; and planetary, human, and animal suffering.

It is easy to become overwhelmed and feel despair. What can be changed, and how can we even comprehend the enormity of the crisis facing our planet? And how can any of this relate to how we choose to feed our companion animals?

The topic of a “sustainable diet” for humans, let alone our companion animals, is a deep and complicated subject, often emotionally charged and wrought with many opinions. I think we can all agree, however, that we want our animals to thrive and be healthy. I believe many of us also want our planet to heal, and to see the humane treatment of all animals, including those consumed by humans and our carnivorous dogs and cats.

In this article, I will attempt to illustrate the current scientific evidence and concerns that guided me to change not only the way I am feeding my own animal companion, but what I am recommending to clients as well. Keep in mind that this is a vast topic, and it’s beyond the scope of this article to illuminate every facet of the environmental, health, and ethical concerns as they pertain to feeding our companion animals.


Growing, harvesting and processing food, all of agriculture, is part of the human activity that is warming the planet. To what extent does animal-based agriculture contribute to the problem? The wealth of climate science is now immense, and many reports and studies measure many parameters. One paramount contribution to global warming is greenhouse gas (GHG) emissions. Estimates of the GHG levels (methane, carbon dioxide, nitrous oxide, fluorinated gases) produced by animal agriculture vary, but almost all point to meat, dairy, and egg production, as well as crops grown solely for animal consumption, as major contributors to the overheating of our planet. Probably the most quoted figure, from a major study done by the United Nations several years ago, puts emissions from animal agriculture at 14% of all GHG.

But now, an extensive new (2021) University of Illinois study of the entire food production system worldwide, published in Nature Food, has upped that percentage considerably. Their model-data integration approach took into account full consistency between subsectors, providing explicit estimates of production and consumption-based GHG emissions worldwide from plant- and animal-based human food in circa 2010 (mean of the 2007 to 2013 period). Researchers collected detailed data on a wide variety of both animal and plant food production from 200 countries.

Their conclusion is that nearly 60% of all GHG can be traced to our food supply systems, and animal products account for almost twice as many emissions as all plant-based foods combined.2 In the elapsed decade, with population growth and rising demand for animal foods, the emissions have risen higher yet, surpassing even those of the fossil fuel and transportation industries.3

Food system inputs beyond GHG emission include land use, deforestation, loss of habitat, depletion of freshwater resources, and pollution of aquatic and terrestrial ecosystems through excessive nitrogen and phosphorus accumulation and use. In addition to requiring more land than plant crops to produce the equivalent protein energy, animal production has considerably greater impacts on water and fossil fuel use, erosion, greenhouse gas emission, fertilizer and pesticide use. The conversion rate of plant-based to animal calories per kg is about 2:1 for poultry, 3:1 for pigs, farmed fish, milk and eggs, and a most inefficient 7:1 for cattle. These are calculations carried out by the United Nations Environmental Program for the calories lost during animal food production.

Over 70 billion animals are slaughtered each year to keep up with the demand for meat. The biggest consumers are rich, mostly Western countries, while developing nations are emulating Western appetites. Animal products are expensive, yet the meat industry still receives huge government subsidies, especially in the United States.

There is a current, encouraging interest in animal-involved regenerative agriculture. But in recent years, the regenerative agriculture movement seems to be driven by those who are promoting meat consumption. If animal-involved regenerative agriculture were used worldwide in the place of concentrated animal feeding operations (CAFOs), that would be a great improvement.

The scientific evidence is clear that the more overall meat consumption is reduced, the more our environment will have a chance to regenerate and heal. Regenerative crop agriculture, restoration of grasslands and forests, and rewilding are of course greatly needed to restore the health and carbon-storing ability of our soils.

See sidebar at bottom left for a look at where companion animal meat consumption figures in all this.


Many guardians of companion animals are interested in plant-based diets for their dogs and cats because of the environmental impacts and humane concerns discussed above. But can dogs and cats eat healthy plant-based diets, or at least significantly fewer animal protein sources? Current research indicates they can, and more studies are coming.

A 2016 article comprehensively reviews the evidence of four studies that examined the nutritional adequacy of vegetarian diets for cats and dogs.5 To obtain additional information, they surveyed 12 pet food companies, and examined the nutritional soundness of meat-based companion animal diets, reviewing the evidence concerning the health status of vegetarian, carnivorous, and omnivorous companion animals. The authors concluded that both cats and dogs may thrive on vegetarian diets, but they must be nutritionally complete and reasonably balanced. They recommended that guardians should also regularly monitor urinary acidity and correct urinary alkalinization through appropriate dietary additives, if necessary.

Another study from the primary author looked at palatability.6 Based on guardian-reported behaviors, the results indicated that vegan pet foods are generally at least as palatable to dogs and cats as conventional meat or raw meat diets, and do not compromise their welfare when other determinants such as nutritional requirements are adequately provided.

Clinical trials are, of course, needed. A 2009 study was the first to demonstrate the potential of a meat-free diet being nutritionally adequate for exercising dogs.7 In a 16-week controlled experiment, a meat-free diet maintained hematological characteristics in sprint-racing sled dogs (Siberian Huskies). Importantly, these findings pave the way for commercial pet food manufacturers to produce nutritionally adequate meat-free diets for dogs.

Dr. Tonatiuh Melgarejo, a clinician-scientist at Western University of Health Sciences in California, and his team of scientific collaborators, are soon publishing their results from a first-of-its-kind plant-based nutrition feeding trial in companion dogs. Fifteen clinically healthy dogs aged one to nine years were followed for a year while being fed a nutritionally-complete commercial plant-based diet. These dogs had all been previously fed a meat-based diet. The dogs were allowed to live at home with their human companions, so were not caged in a laboratory. They were routinely examined and followed with relevant tests to study cardiac function (echocardiogram), blood (serum) chemistry and hematology, as well as vitamin and amino acid profiles and microbiome measurements, accumulating hundreds of biomarkers. A preliminary summary reveals that all these dogs remained clinically healthy at the end of 12 months. The study results so far look promising, and support the idea that dogs can live as healthily, if not healthier, on plant-based diets as they can on meat-based diets. What is particularly helpful is that this study has produced a significant amount of valuable new data.8

If an animal has chronic health issues, transitioning to plant-based diets may take time and patience, but this is true for any feeding change. Using holistic healing modalities can aid in the transition.

I don’t see that novel “meat alternatives” are needed to feed and nourish our companion animals. Healthy and sustainable food already exists in the form of legumes, grains, nuts, seeds, vegetables, and fruits. Much knowledge has been accumulated from those who have been feeding plant-based diets for decades, whether they use a commercial complete diet or one that is home-prepared.10 Today, more clinical research is advancing our understanding of feeding plant-based diets to dogs. Many recipes, supplements, and commercial brands are available to help an animal guardian make the change, and more are on the way.

In closing, navigating our global situation and implementing ways to try and change the course of our climate crisis can feel overwhelming. To reference Jane Goodall’s work and teachings around hope, we can, every single day, make a choice to buy or do something that has a lower impact on our environment. We can choose something we care about and that is doable, right now. Choosing to feed our animal companions a plant-based diet, or at least significantly less animal protein, is a step we can take right now without the need for developing new speculative technologies. That choice would allow care for all animals, and take us a step forward to helping heal the Earth.

1 AR6 Climate Change 2021:The Physical Science Basis. Intergovernmental Panel on Climate Change. August 9, 2021.

2 Xu X, Sharma P, Shu S, et al. Global greenhouse gas emissions from animal-based foods are twice those of plant-based foods. Nat Food. 2021; (2): 724-732.

3 Knight A.

4 Okin GS. Environmental impacts of food consumption by dogs and cats. PLOS ONE. 2017; 12(8).

5 Knight A, Leitsberger M. Vegetarian versus meat-based diets for companion animals. Animals. 2016; 6(9);57.

6 Knight A, Satchell L. Vegan versus meat-based pet foods: Owner-reported palatability behaviours and implications for canine and feline welfare. PLOS ONE. 2021; 16(6).

7 Brown, W, Vanselow, B, et al. An experimental meat-free diet maintained haematological characteristics in sprint-racing sled dogs. British Journal of Nutrition. 2009;102:1318–1323.

8 Personal Communication, 28 Sep 2021, with Tonatiuh Melgarejo, DVM, MS, PhD; Tenured Professor of Translational Medicine and Antimicrobial Resistance; College of Veterinary Medicine, Western University of Health Sciences, Pomona, CA. Dr. Melgarejo is also the co-founder of the Western U True One Medicine Initiative (TOMI), which serves to advance species-spanning medicine through evidence-based research and ethical decision-making in science, hereunder the study of plant-based nutrition in companion dogs.

9 Pitcairn, R. Feeding the dog in the 21st century. Dog’s Naturally Magazine. March/April 2015.

10 Pitcairn, R, Pitcairn, S. Dr. Pitcairn’s Complete Guide to Natural Health for Dogs and Cats. 4th ed. Rodale, 2017


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