Why do cats eat grass
Cats eat grass primarily for fiber to aid hairball passage, though recent evidence suggests it may also serve as a source of folate or a way to induce vomiting when they feel unwell.
Most cats eat grass to aid the passage of hairballs or to induce vomiting when they feel unwell, driven by a need for fiber rather than hunger. This behavior is common across many "carnivorous" species, yet the exact motivation varies by individual and context.
Fiber and the hairball mechanism
The most widely accepted explanation is that grass provides insoluble fiber that acts as a mechanical irritant to the stomach lining, triggering regurgitation. A 2025 microscopy study of regurgitated matter confirmed that leaf trichomes are often interlocked with hair, suggesting the plant material helps bind loose fur and move it out of the digestive tract. This function supplants the need for cats to nibble on houseplants or lawn grasses, which may be treated with pesticides or fertilizers that are toxic to felines.
Behavioral evidence is mixed
Despite the mechanical theory, surveys of pet owners have not observed specific behavioral changes that definitively support the idea that cats only eat grass when suffering from hairballs. Many cats consume grass without subsequently vomiting, and some do so regularly without any apparent gastrointestinal distress. This suggests the behavior is not solely a symptom of illness but may be a normal part of feline foraging behavior, similar to how other carnivores ingest plants for specific nutrients or to clear their systems.
What is actually in the grass?
Cat grass is typically composed of young cereal grains like wheat, barley, oat, or rye, harvested at the sprout or microgreen stage between 7 and 14 days of growth. At this stage, the grass is rich in soluble fiber, chlorophyll, and water-soluble vitamins, including certain B vitamins. While cats are obligate carnivores, they may seek out these plant materials to supplement their diet with folate or other micronutrients that are less abundant in their standard meat-based diets.
When it becomes a medical issue
While occasional grass eating is normal, persistent vomiting warrants clinical evaluation to rule out gastrointestinal disease. If a cat is vomiting frequently, losing weight, or showing signs of lethargy, the grass consumption may be a symptom of an underlying condition rather than a solution. Owners should distinguish between the occasional regurgitation of a hairball and the repetitive vomiting associated with illness, which requires veterinary intervention.
Safe cultivation and selection
For owners wishing to provide cat grass, it is best to grow it indoors in shallow trays using potting media or hydroponic mats, ensuring the plants are cut or presented within 1 to 2 weeks. The process mirrors growing microgreens, requiring dense sowing, a few days of dark germination with high humidity, and bright light after emergence. It is crucial to avoid using commercial lawn grasses that may have been treated with chemicals, as these can be harmful if ingested by cats.
Why they do not just eat houseplants
Cats often prefer specific grasses over the random assortment of houseplants found in a home. This preference likely stems from the specific texture and fiber content of cereal grasses, which are more effective at aiding digestion than the leaves of ornamental plants. Additionally, providing a dedicated source of safe grass reduces the likelihood of a cat ingesting toxic species like lilies or sago palms, which can be fatal.
In summary, grass eating is a multifaceted behavior rooted in the need for fiber, potential nutrient supplementation, and the mechanical clearing of hairballs. While the exact trigger for individual cats varies, providing a safe, organic source of grass is a practical way to support their natural instincts without risking exposure to toxic plants.