Plant-based diets

As people become more aware of their health, nutrition, and environmental impact, many have shifted towards a plant-based diet and more resource-conscious lifestyle. Some pet owners have even chosen to extend their own beliefs and preferences to their pets, opting for plant-based diets for their dogs and cats as well. Plant-based pet diets are becoming increasingly popular, with the help of marketing pitches that explain why plant-based pet food is healthier, more sustainable, and more ethical. However, these claims are often unfounded and have no real basis in science. Pet owners who are considering plant-based pet foods should seek to understand the nutritional implications of feeding these diets to their pets.

Definitions

Vegetarian diet

A diet made without meat or fish, but may still contain eggs or dairy

Vegan diet

A diet made without any animal products

Plant-based diet

A diet consisting of mainly plant products and containing little or no animal-source products. This term can be used to describe vegetarian or vegan diets, and is the term that will appear throughout this article.

Why do people choose plant-based diets for their pets?

Pet owners often choose to feed their pets plant-based diets for similar reasons as to why they chose the lifestyle themselves. Vegetarianism and veganism are incredibly personal lifestyle choices. They may work well for some people, and not so well for others. Even so, it is very difficult for vegetarians to have complete and balanced diets; studies have shown that humans who consume diets low in animal ingredients are deficient in several nutrients.

Environmental awareness

Many people believe that farm animals, namely cattle, are to blame for climate change and greenhouse gas production. However, according to the EPA, agriculture makes up less than 10% of total greenhouse gas emissions in the US, with livestock being less than half that (~4%). Transportation, electricity, and industry are all much bigger contributors of emissions waste (77% between all three).

Some people believe that food animal production is incredibly wasteful. Over the years, however, selective animal breeding, better management, and improved farming practices have allowed farmers to produce more product (meat, milk, eggs) using less animals, land, feed, and water. This is an incredible example of how science and agriculture have worked together for the good of the US population’s nutrition.

Another common argument against animal agriculture is that it takes more land to raise livestock than crops. While animal agriculture does make up about ⅔ of all agricultural land, this is because most agricultural land is non-arable, meaning that crops couldn’t be grown on the land even if the animals weren’t there.

It is also important to note that livestock are not competing with humans for food. They eat plants that humans and other animals cannot consume. For example, they eat grass as well as byproducts from the corn, cotton, and soy industries. Byproducts of these industries are cornstalks (principal product: corncob), cotton hulls (principal product: cotton fiber), and the leafy part of the soy plant (principal product: soybean). Livestock recycle our “leftovers,” ensuring these byproducts are not wasted.

Finally, it is important to remember that pet food is an essential part of animal agriculture. The parts of slaughtered animals that are not used for human food, textiles, medicine, or other industries are used in pet foods. These parts, such as internal organs, bones, and meat meal, would be wasted if not for the pet food industry. Re-purposing these byproducts is an awesome form of recycling. (To learn more about this topic, visit By-products and meat meal.) 

Ethical considerations

Another common reason people choose to abstain from eating animal products is due to ethical concerns. Many vegetarians do not wish animals to die for their sake. However, in regards to dogs and cats–with few exceptions–livestock are not slaughtered specifically for pet foods. Animals are slaughtered for human consumption and the by-products are recycled into pet food.

There are dozens of laws and regulations nationally and state-to-state that ensure animal welfare and safe handling in farming and slaughter. The OIE defines animal welfare as: “how an animal is coping with the conditions in which it lives. An animal is in a good state of welfare if it is healthy, comfortable, well nourished, safe, able to express innate behavior, and if it is not suffering from unpleasant states such as pain, fear, and distress. Good animal welfare requires disease prevention and veterinary treatment, appropriate shelter, management, nutrition, humane handling and humane slaughter/killing.” Welfare regulations ensure the animals raised for meat, milk, and eggs in the US are treated with care and respect.

Health concerns

Many people believe that a plant-based diet is healthier than eating animal products. There have been many studies performed in human health/nutrition that tell us to eat less meat and more animal products. However, these studies are incredibly conflicting, and a meta-analysis in 2020 confirmed that there is currently no definitive scientific evidence showing that eating meat is harmful to human health.

Furthermore, even if there were data showing meat is bad for humans, this could not be extrapolated to dogs and cats. Dogs and cats have much different nutrient requirements than we do, and it is inappropriate to suggest that they should eat the same as humans.

Concerns with plant-based diets

Species requirements

Dogs are omnivores, meaning that the nutrients they require can come from both plant and animal sources. Dogs have no specific requirements for animal-source nutrients. However, cats are obligate carnivores, meaning they have requirements for certain nutrients that are only found in animal ingredients (e.g., taurine and arachidonic acid). This means that while dogs technically can survive on a fully plant-based diet, cats cannot.

Digestibility and bioavailability

Digestibility refers to how well an animal’s digestive system can break down an ingredient and absorb its nutrients. Studies have shown that animal-source ingredients are more digestible than plant-source ingredients.

Bioavailability refers to how well an animal’s body can utilize the nutrients present in an ingredient. Studies show that several nutrients are more bioavailable when they come from animal-source ingredients.

Nutrition

To gain a better understanding of the nutritional needs of dogs and cats, visit Nutrient requirements. 

Protein

Plants are low in percent protein, i.e., most of the plant is made up of other nutrients such as carbohydrate and fiber. Plants also have lower chemical scores and biologic values than do animal-source ingredients, due to their limiting amino acids. This does not mean that plants are poor sources of protein, however. Plants can be an excellent source of complementary protein when used in conjunction with animal proteins, but when plants are the sole source of protein, many different plants must be used to balance all the essential amino acids that our pets require in their diets.

Plants also have a lower protein digestibility than do animal-source proteins. Therefore, plants require extra cooking and processing so they can become more digestible.

Taurine is an amino acid of concern with plant-based diets. Dogs technically do not require taurine; they can synthesize it from its precursors methionine and cysteine. However, cats do have a dietary requirement for this nutrient, which is only found in animal proteins.

Fat

Arachidonic acid is a fatty acid that is found only in animal fat sources. Arachidonic acid is required by cats.

EPA and DHA are two of the Omega-3 fatty acids. The best source of these nutrients is fish oil, though they can be found in algae (which is technically not a plant). These fatty acids are required by growing (puppies and kittens) and reproducing (pregnant and lactating) animals.

Fiber

Fiber is a big concern with plant-based diets. These diets often have very high levels of fiber, much higher than traditional diets. Of course, this is because many plants are high in fiber.

High fiber decreases total digestibility of the diet, as well as protein digestibility. This can lead to problems with digestion and nutrient deficiencies. High fiber also increases bile acid secretion, which degrades the amino acid taurine, and could lead to taurine deficiency in both dogs and cats. Finally, high fiber may also decrease uptake of certain minerals, such as calcium, magnesium, and phosphorus.

Vitamins

Vitamin A comes in two forms: beta-carotene (from plants) and retinoids (from animals). Dogs have the ability to convert beta-carotene from plants into retinol (vitamin A). However, cats do not have this ability and thus require animal-source retinoids in their diets.

Vitamin D also comes in two forms: D2 (from yeast and fungi) and D3 (from animals). Technically, vitamin D2 can be converted to D3, but there is not enough scientific evidence showing that dogs and cats have the ability to do this sufficiently. Thus, they require vitamin D3 in their diets.

Vitamin B12 is found only in animal ingredients. However, it can be made synthetically and supplemented into the diet.

Minerals

The bioavailability of several minerals, such as iron, zinc, magnesium, and phosphorus is very poor when they come from plant sources. This is due to their chemical formulations.

The presence of certain compounds in plants such as oxalates and phytic acid also cause decreased absorption of minerals such as calcium, zinc, iron, and manganese.

The importance of complementary nutrients

While diets made with only plant products may not be ideal for dogs and cats, this isn’t because the plants themselves are bad for our pets. Dogs and cats require over 40 nutrients in their diets, all in different proportions. Some of these nutrients come from animals, others from plants, and together they complement one another and balance the nutrition in the diet. When a diet is made with both plant and animal ingredients, and is formulated properly, they form a complete and balanced diet.

Types of plant-based diets

Homemade

Homemade diets can work wonderfully for many pets when formulated and prepared correctly. However, most homemade diets, especially plant-based diets, are not nutritionally complete and balanced. Pet owners seeking to feed homemade diets must consult with a board-certified veterinary nutritionist to ensure the diet is complete and balanced. To learn more, please visit Homemade diets.

Commercial OTC

There are several commercial over-the-counter plant-based dog and cat diets on the market today. While these diets may show they meet AAFCO formulations, there are no feeding trials showing that dogs and cats can thrive on these diets. There is also not enough research showing their safety; in fact, studies have actually shown that many OTC plant-based diets are not complete or balanced, their nutrient levels do not meet AAFCO guidelines, and many of their labels do not comply with AAFCO regulations.

Therapeutic

To gain a better understanding of what therapeutic diets are, the science behind them, and how they are regulated, click here. 

There are only a few therapeutic plant-based diets on the market today. They are produced by science-based pet food companies who employ board-certify veterinary nutritionists and perform research and feeding trials on their diets. There is extensive scientific research showing the safety and digestibility of therapeutic diets. These diets are often a good choice for pets with digestive conditions, or with allergies to multiple animal ingredients (see Food allergies for more information).

It is important to remember that we should not anthropomorphize our own beliefs onto our pets. Dogs and cats are not humans, and they do not have the same nutrient requirements or preferences that we do.

It is best to avoid commercial over-the-counter plant-based diets for both dogs and cats. However, some pets may require a therapeutic diet to treat certain health conditions. It is best to speak with your pet’s usual veterinarian if you are concerned about your pet’s health.

If you are adamant about feeding your pet a plant-based diet, it is best to choose a diet formulated by science-based pet food manufacturers. Visit How to pick a pet food, part 1 to learn how to evaluate pet food companies. Pets who eat plant-based diets should visit the veterinarian at least twice per year, to ensure they are staying healthy on these diets.

Another great alternative for pet owners who are against feeding meat to their pets is to get an herbivorous animal such as a rabbit or guinea pig.

Resources

Primary literature