Why Do Cats Eat Grass - The Mystery is Solved!

If your cat goes outside, the chances are that you have seen them eating grass. You may have even seen grass in their vomit.

But cats aren't cows, so why do cats eat grass?


Eating grass is a really common activity for cats. In fact, over 7 out of 10 cats are reported by their owners to regularly enjoy tucking into a meal of the green stuff.

There’s a good chance then that your cat is also a grass-muncher, whether you see them eating grass or not!

Why Do Cat’s Eat Grass

Age-Old Theories

  • Dietary deficiencies

  • Hairball elimination

  • An unwell cat making themselves vomit

  • Stress relief

Over the years, there have been a number of theories about why cats eat grass. Pica is the act of eating substances not normally thought of as food, and is often thought of as a marker of a poor diet. The individual (in this case your grass-eating cat!) is thought to be trying to rectify this deficiency by eating something peculiar.

The theory with grass is that it could be being used as a source of folic acid, something found in grass juice, which is important for growth and the intestinal digestive process.

Other proposed motivations behind your cat eating grass include getting rid of hairballs, most likely through vomiting but also by making any hair pass before it starts to clump in the stomach.

Purging the stomach comes next with some thinking that a cat who has eaten something they shouldn’t innately knows to eat grass to make themselves vomit.

And then finally, stress relief is another proposed reason. Just one of many stereotypies that could be performed to potentially release endorphins and help an individual cope with a stressful event.

The Mystery is Solved!

A recent study specifically looked into why cats eat grass. In the vast majority of cases, 91% in fact, the owners said their cat didn't appear to be unwell before they ate grass and didn't vomit afterward either. That pretty much blown the self-induced vomiting theory out of the water!

Instead, the scientists proposed that regular plant-eating by domestic carnivores (that is your cat!) eating grass is a reflection of an innate, in-built behavior passed down from a wild ancestor who regularly ate grass.

This grass-eating behavior has also been shown in large wild cats through the examination of their feces, which has shown a lot of indigestible plant material to be present in their scats.

It is thought that this innate behavior developed to help with the elimination of parasites from the gut.

Eating plants, particularly by eating non-digestible plants, the result is that the intestines have to work more and contract harder. This short-term boost to intestinal motility then results in the elimination, or at least control of, intestinal worms and other parasites.

As well as cats, this behavior has also been shown in primates whereby eating indigestible vegetation purges the system of intestinal parasites.

So there you have it! Cats eat grass because of an inbuilt behavior, with the result being that intestinal parasites are better controlled.

As for helping to get rid of hairballs, it is certainly possible that eating grass does also help with this as well. Although not mentioned in the study, it would make sense that the increased intestinal contractions are also going to help clear out anything else that happens to be within the stomach or intestines.

And as for those cats that are sick after eating grass, it may just be that they are eating the wrong sort of grass or other vegetation that is not completely safe for them to eat.

Cat-owner Advice

The team of scientists investigating the reasons behind cats eating grass even gave some advice to the cat-owning public. Their advice is to provide your cat with a safe form of grass for them to eat. Either planting it in your garden or having it in a readily accessible pot inside.

Safe grass varieties include ryegrass and wheatgrass which you can also buy as seed kits (on amazon here) and indoor “feeders” designed to prevent your cat from tipping it upsidedown or digging and making a real mess indoors. Check out the indoor planters here.

Helping your cat to safely express their natural grass-eating behavior may not only improve their intestinal health, but will also lead to them being less stressed and happier.

Even indoor cats deserve to eat grass!