Can Cats Eat Natto?

No, cats shouldn't eat natto—and the reasons might surprise you. Natto is fermented soybeans with a sticky, stringy texture and a very strong smell. That smell attracts some cats, making them curious about this weird human food. But curiosity doesn't mean it's safe. Natto is packed with nutrients that humans value—vitamin K2, protein, probiotics—but cats don't process soy the same way humans do. Their digestive systems aren't designed for fermented plant proteins. What makes natto a health food for humans makes it a digestive nightmare for cats.

Natto is not toxic in the way chocolate or grapes are toxic. A tiny taste won't poison your cat. But it's not safe as a regular food or even as an occasional treat. The fermentation process that makes natto beneficial for humans creates compounds that cats can't digest well. Cats lack the gut bacteria to break down fermented soy properly. The result is often gas, bloating, diarrhea, or vomiting. Many commercial natto products also come with sauce packets that contain soy sauce (high sodium), mustard, or other seasonings—all problematic for cats. Even plain natto without seasonings is problematic because of the soy itself.

Most people don't intentionally feed natto to cats. It's usually curiosity—your cat smells the strong, pungent odor of natto and investigates. Some cats are attracted to fermented smells the same way they're attracted to fish. A few owners wonder if the probiotics in natto might help their cat's digestion, or if the protein content makes it a good supplement. But natto's benefits are specific to human biology. The probiotics are strains that support human gut health, not feline gut health. The protein is plant-based, which cats can't utilize as efficiently as animal protein. And the vitamin K2, while beneficial for humans, isn't something cats need to supplement—they get adequate vitamin K from their diet.

Natto comes in various forms, all problematic for cats.

Cats are obligate carnivores designed to eat meat, not fermented plants. Natto is soybeans that have been fermented with bacteria—specifically Bacillus subtilis. This fermentation creates compounds like nattokinase and increases vitamin K2 content. For humans, these are health benefits. For cats, they're just difficult-to-digest substances their bodies don't know what to do with. Cats lack the digestive enzymes to efficiently break down plant proteins. The fermentation makes it even harder because the molecular structure has changed. The sticky, stringy texture of natto can also be uncomfortable in a cat's mouth and throat. Some cats may vomit just from the texture alone, before digestion even begins.

Problems can occur even from small amounts.

No. This is a common misconception. The probiotics in natto—primarily Bacillus subtilis—are beneficial for human gut health. They help humans digest food, support immune function, and may have other health benefits. But cats have completely different gut bacteria than humans. The probiotic strains that help humans don't colonize feline intestines the same way. If your cat needs probiotics, there are cat-specific formulations that contain strains like Enterococcus faecium or Bifidobacterium that actually work in feline digestive systems. Giving natto for probiotics is like giving fish food to a cat because they both eat—it doesn't work that way.

If you're interested in natto because of probiotics, there are much better ways to support your cat's digestive health. Cat-specific probiotic supplements contain strains that actually colonize feline guts. These come in powder or capsule form that you can mix with food. Some high-quality cat foods include probiotics in their formulas. Pumpkin puree (plain, not pie filling) can help with digestive issues. But before adding any supplement, talk to your vet. Your cat might not need probiotics at all. Healthy cats eating quality cat food typically have balanced gut flora without supplementation.

Absolutely not. Kittens have even more sensitive digestive systems than adult cats. Their gut bacteria are still developing, and fermented soy could cause severe digestive upset.

If your cat had a small taste of plain natto, they'll probably have some digestive upset but be okay. Watch them closely.

Generally no. Fermented foods are popular health foods for humans—kimchi, sauerkraut, natto, kombucha. But cats don't benefit from fermented foods the way humans do. The fermentation process creates compounds and bacteria that humans can utilize but cats can't. Fermented vegetables are doubly problematic because cats are carnivores who don't digest plant matter well, and the fermentation makes them even harder to digest. Some fermented foods like kimchi or sauerkraut also contain high sodium, garlic, or other ingredients that are dangerous for cats. If you want to support your cat's gut health, use cat-specific probiotics, not fermented human foods.

Soy is not toxic to cats, but it's not ideal either. Some commercial cat foods include soy as a protein source, usually in lower-quality brands. Cats can digest some soy, but not as efficiently as animal protein. Soy contains phytoestrogens—plant compounds that mimic estrogen—which may affect hormone levels in large amounts. Some cats develop allergies to soy. Fermented soy like natto is even more problematic because the fermentation process changes the protein structure. If your cat needs protein, it should come from animal sources—meat, fish, or eggs—not from soy products. Quality cat food uses animal protein as the primary ingredient.

No. Cats synthesize their own vitamin K in their intestines and get adequate amounts from their diet. Vitamin K2 is important for humans—it supports bone health and cardiovascular function. That's why natto, which is extremely high in K2, is considered a superfood for humans. But cats don't have the same vitamin K requirements. They produce vitamin K through gut bacteria and get enough from meat-based diets. Supplementing with natto isn't necessary and could potentially cause digestive problems that outweigh any theoretical vitamin benefit. If your cat has a medical condition requiring vitamin K supplementation, your vet will prescribe an appropriate form—not natto.