How are dogs’ and cats’ digestive systems different? Let’s break down how their dietary needs differ.

When you live with both a dog and a cat, you may find yourself wondering, “Can’t they eat the same food?” or “My cat ate some dog food—is that okay?”

Both are familiar pets that share our homes, but in fact, their digestive systems and nutritional needs differ considerably.

Here are three things you’ll learn in this article:

• Why dogs are called “omnivores” and cats “carnivores,” and how their digestive systems differ
• How their nutritional needs differ—especially their protein needs—and why cats need taurine
• How their eating habits differ, and what neither dogs nor cats should be fed

This article draws primarily on the Ministry of the Environment’s “Pet Food Guidelines for Pet Owners.”

Dogs are “omnivores,” cats are “carnivores”—their lifestyles with humans shaped the difference

The Ministry of the Environment’s guidelines sum up the difference between dogs and cats as follows:

• Dogs are omnivores: They became increasingly omnivorous as they lived alongside humans over many generations.
• Cats are carnivores: They have retained their carnivorous nature despite living alongside humans.

“Omnivore” here means an animal that can eat both meat and plants and obtain nutrients from them. It does not mean “can eat anything without a problem.” As we’ll explain later, dogs also need more protein than humans do.

Dogs have adapted to digest starch more easily

Dogs are thought to have evolved from ancient wolves as they began living alongside humans. Wolves primarily eat meat, but dogs have gradually changed since then.

A study published in the scientific journal Nature in 2013 closely compared the genes of dogs and wolves. The researchers found dog-specific changes in genes involved in digesting starch—a component abundant in rice, bread, and potatoes—and metabolizing fat. The study reported that dogs digest starch more easily than wolves.

The researchers suggest that being able to thrive on a starch-rich diet, as well as the meat-based diet of wolves, was an important early step in dogs’ adaptation to living with humans.

Cats still have digestive systems suited to digesting meat

Cats, by contrast, are descended from carnivorous wildcats. According to materials from the Japan Pet Food Association, cats remained carnivores after being domesticated, and this is reflected in their digestive systems.

• Short digestive tract: The digestive tract—the passage food travels through—is about four times the length of the body, considerably shorter than in omnivores and herbivores.
• Well-developed small intestine, but relatively modest large intestine: This structure is suited to digesting and absorbing the protein and fat in meat.
• Almost no cecum: The cecum is a pouch-like part at the junction of the small and large intestines. As a result, cats cannot make good use of the dietary fiber found in plants.

In other words, a cat’s digestive system is better suited to digesting and absorbing protein and fat from meat than to processing plants.

Cats cannot taste sweetness

There’s another interesting difference. According to the Ministry of the Environment’s guidelines, dogs love sweet foods, but cats cannot taste sweetness. They are also said to lack the enzyme needed to break down fructose, a sugar found in fruit and other foods.

Even if your dog craves sweets, be careful not to give it too much sugar or fruit, as these can contribute to obesity.

Nutritional needs differ too: cats need especially large amounts of protein

Like humans, both dogs and cats need to get protein, fat, carbohydrates, minerals, vitamins, and other nutrients from food. What differs is the proportion they need.

Even with the same calorie intake, their protein needs differ

The Ministry of the Environment’s guidelines include a graph comparing the recommended amount of protein in a 1,000-kcal diet. In other words, it compares how much protein each needs when eating the same number of calories.

• Humans (ages 30–49): 23 g for men, 25 g for women
• Dogs: 45 g
• Cats: 65 g

By this calculation, dogs need about twice as much protein as humans, while cats need even more—about 1.4 times as much as dogs (the figures for dogs and cats are based on standards set by the Association of American Feed Control Officials, or AAFCO).

The same guidelines also compare the proportion of nutrients in an average diet. Protein makes up 18% of a dog’s diet and 26% of a cat’s; fat makes up 5.5% and 9.0%, respectively (as a percentage of weight, excluding water). Cats’ diets contain a higher proportion of protein and fat than dogs’ diets do.

Taurine is essential for cats

Another important component of cat food is taurine. Taurine is a nutrient that plays a role in the body and is found in abundance in seafood and animal organs.

Humans and dogs can produce taurine in their bodies. However, according to the Ministry of the Environment’s guidelines, cats cannot produce enough taurine on their own. A deficiency may lead to health problems such as eye disease (retinal atrophy) and heart disease (dilated cardiomyopathy).

That’s why cats need to get taurine from their food. This is especially important if you mainly feed your cat homemade meals.

Choose food made specifically for dogs and cats

Given these differences, it’s generally not recommended to have a dog and cat share the same food.

Dogs and cats need different proportions of protein and fat, and cats also need taurine. Dog food is made to meet dogs’ needs. As a general rule, feed dogs food made for dogs and cats food made for cats.

If you have both pets, it may help to feed them in separate places or at different times so they don’t eat from each other’s bowls.

The Ministry of the Environment’s guidelines recommend choosing “complete and balanced” food as the mainstay of your pet’s daily diet. Complete and balanced food is formulated to provide the right balance of nutrients to maintain health when served as the main daily meal with fresh water. Check the label and follow the recommended serving amount.

Eating habits differ too: dogs eat “a lot at once,” while cats eat “small amounts many times”

Dogs and cats also have different eating habits. The Ministry of the Environment’s guidelines recommend feeding them in ways that suit each animal.

Dogs: Divide the daily amount into several meals

Dogs have stomachs large enough to hold a full day’s worth of food at once. As a result, they tend to eat whatever is in front of them until they’re full.

If you feed your dog only once a day, it may gulp down the food and choke, or gain weight. Divide the daily amount into several meals.

Cats: Let them eat small amounts several times a day

Cats tend to eat small amounts many times throughout the day and night.

Recommended options include dividing the daily amount into two or three meals, or leaving out dry food so your cat can eat whenever it wants. If you leave food out, keep the bowl clean and replace the food regularly. Wet food and homemade meals, which contain more moisture, spoil easily, so remove any leftovers promptly.

Always provide fresh drinking water

According to the Ministry of the Environment’s guidelines, water makes up 60–80% of a dog’s or cat’s body. They get most of the water they need—90–95%—from drinking water and food.

Dry food in particular contains little moisture, so always keep fresh water nearby. For cats, it’s recommended to place water bowls in several locations.

Foods you should never give to dogs or cats

Some foods that are harmless to humans can be harmful to dogs and cats. The Ministry of the Environment’s guidelines list the following as foods to avoid:

Food	What the guidelines say
Onions, green onions, garlic chives, and garlic	Contain substances that destroy red blood cells. These substances are not broken down by cooking, so take care with processed foods such as hamburgers, as well as cooking liquid and extracts.
Chocolate	May cause vomiting, diarrhea, seizures, and other symptoms.
Gum and other products containing xylitol	Even small amounts may cause low blood sugar, vomiting, and other symptoms in dogs.
Chicken bones	Can splinter lengthwise into sharp pieces and injure the throat or digestive tract.
Raw seafood (squid, octopus, shrimp, crab, etc.)	In cats, it may lead to vitamin B1 deficiency and related health problems. Always cook it thoroughly.
Grapes and raisins	Can cause kidney failure. In particular, do not feed grape skins.

Other foods listed as requiring caution include liver (if fed in excess), spinach, coffee and tea, raw meat, spices, raw egg whites, dried sardines, and nori seaweed.

Human leftovers and foods such as ham may also contain too much salt for dogs and cats. If you want to give them cheese, choose a product made specifically for dogs or cats.

If your pet accidentally eats something it shouldn’t, or seems unwell, don’t try to assess the situation on your own—contact your regular veterinary clinic right away.

Frequently asked questions

Q. My cat ate a little dog food. Is that okay?

Dog food is formulated for dogs, so its nutritional balance differs from what cats need. The main concern is if this happens every day. Take steps to prevent it from becoming a habit, such as using separate bowls or feeding them in different places. If your cat seems unwell, consult your veterinarian.

Q. If dogs are omnivores, can they eat the same food as humans?

That’s not recommended. Dogs need more protein than humans, and human food may contain too much salt for dogs or ingredients they must not eat, such as onions. As a general rule, feed your dog food made for dogs.

Q. Can I feed my cat vegetables or fruit?

As a general rule, choose food made for cats. Cats cannot make good use of dietary fiber and are said to lack the enzyme needed to break down fructose. Some fruits, such as grapes and raisins, must not be fed to cats (see the table above). If you want to add something to your cat’s diet, consult your regular veterinarian about whether it’s safe and how much to give.

Summary: Even if they’re both pets, their diets should be treated separately

Here are the three key takeaways:

• Dogs are omnivores; cats are carnivores. Dogs have adapted to digest starch more easily, while cats still have short digestive tracts suited to digesting meat.
• Their nutritional needs differ. For the same calorie intake, cats need more protein than dogs and must also get taurine from their food.
• Their eating habits differ too. Divide a dog’s daily food into several meals, while allowing a cat to eat small amounts throughout the day. Always provide fresh water.

One thing you can do today is check your pet’s food package to see whether it says “for dogs” or “for cats” and “complete and balanced,” and to confirm the recommended serving amount.

You may also find these related articles helpful.

• Supporting your dog’s or cat’s gut health: Get started by adding a spoonful to their food
• What is gut flora? A simple guide to “good, bad, and opportunistic bacteria”

Add a little kestose to your dog’s or cat’s food

The information above is general information about the physiology and diets of dogs and cats. It does not demonstrate the effects of kestose.

Nakaya Shoten’s kestose is a food product made with 100% kestose, a type of oligosaccharide. It is a simple oligosaccharide made up of three sugar units and has a mildly sweet taste (30 sachets of 3 g each).

The sources cited in this article do not discuss giving kestose to dogs or cats. If you choose to give it to your pet, start by sprinkling a very small amount over its regular food and monitor how it responds. Depending on the pet, it may cause loose stools. If this happens, stop giving it and consult your veterinarian. For pets with existing medical conditions or other health concerns, consult your regular veterinarian first.

• Kestose, 3 g × 30 sachets (single purchase)
• Kestose, 3 g × 30 sachets (subscription)

For details such as pricing, please see the product page.

This column provides general information about food products and is not intended to treat or prevent disease. If your pet has a pre-existing condition or you have concerns about its health, please consult your regular veterinarian before adding this product to its diet.

Sources

• Ministry of the Environment, “Pet Food Guidelines for Pet Owners: Protecting the Health of Dogs and Cats” (revised 2018) https://www.env.go.jp/nature/dobutsu/aigo/2_data/pamph/petfood_guide_1808.html
• Japan Pet Food Association, “Pet Food Sales Advisor” training materials (sample), Cat digestive system https://petfood.or.jp/assets/kentei_assets/pdf/sampletxt_02.pdf
• Axelsson E, et al. “The genomic signature of dog domestication reveals adaptation to a starch-rich diet.” Nature 495:360–364 (2013) https://www.nature.com/articles/nature11837