Why Do Dogs Eat Grass? The Science Behind This Common Canine Habit
- Kayleigh Adams
- Oct 15, 2025
- 3 min read
Updated: Oct 19, 2025
With the arrival of spring, many dogs, including Hadēs, begin their yearly ritual of grazing on fresh grass.
But is this normal, or should we be worried?
The truth is, grass-eating (also called “pica”) is a very common and mostly harmless behaviour, seen in both wild and domestic dogs. While it can look strange to us, it often has a clear biological basis. Let’s explore some of the science behind why dogs do this.
Enrichment and Instinct
For many dogs, eating grass isn’t a problem at all, it’s simply instinctive behaviour linked to their wild ancestry.
Wild canids such as wolves and foxes have been observed consuming plant matter, including grass, to stimulate digestion and assist in natural cleansing. This behaviour likely evolved because grasses contain fibre and phytonutrients that help move material through the gut.
In domestic dogs, this instinct remains, and spring grass, rich in moisture and slightly sweet-tasting due to higher sugar content, is especially tempting. Chewing grass can also stimulate saliva production and provide sensory enrichment, similar to how chewing toys or licking mats do.
So sometimes, your dog is just satisfying an ancient urge to graze!
Nutritional Self-Selection
Another explanation is nutritional self-selection, where dogs instinctively seek out certain foods to fill minor nutrient gaps.
Grass contains chlorophyll, the green pigment responsible for photosynthesis in plants. While dogs can’t absorb chlorophyll directly from whole grass due to cellulose, the tough plant fibre they can’t digest, chlorophyll itself supports:
Liver detoxification (by aiding phase II conjugation enzymes)
Blood oxygenation and red blood cell health (chlorophyll has a structure similar to haemoglobin)
Anti-inflammatory effects through its antioxidant compounds
Gut health, by promoting the growth of beneficial bacteria
Since dogs lack the enzyme cellulase, they can’t break down plant cell walls efficiently. That’s why grass often reappears in stools looking just as it went in!
If your dog’s diet lacks green foods, they might instinctively try to top up these compounds through grazing, even though it’s not the most efficient method.
To provide bioavailable chlorophyll and plant nutrients, add finely chopped, steamed, or blended greens like:
Kale
Spinach
Broccoli
Green beans
Curly parsley
Spirulina or chlorella powder
These sources are easier for the body to absorb and deliver chlorophyll, magnesium, and antioxidant compounds such as lutein and beta-carotene.
Digestive Upset and the Gut-Brain Connection
Grass eating can also occur when a dog feels nauseous or has mild gastrointestinal discomfort. The rough texture of grass can mechanically stimulate the stomach lining and help trigger vomiting, a natural way for dogs to expel indigestible material, bile, or irritants.
This ties into what scientists call the gut-brain axis, a communication pathway between the digestive system and the nervous system. When a dog’s stomach feels off, sensory signals from the gut may trigger instinctive behaviours like grass eating to self-soothe or relieve nausea.
Common triggers for nausea include:
Empty stomach or bile reflux (especially in the morning)
Eating too quickly
Sudden diet changes
Minor bacterial imbalances in the gut microbiome
If your dog eats grass and vomits immediately afterward, it’s likely a temporary response to stomach discomfort. But if it becomes frequent, it’s worth investigating gut microbiome balance and supporting digestion with prebiotics and probiotics.
Look for signs such as:
Excessive drooling
Lip licking
Restlessness or lethargy
Dry heaving or stomach clenching
These can signal mild nausea, acid reflux, or early digestive inflammation.
The Role of Fibre and Detoxification
Grass provides insoluble fibre, which passes through the digestive system largely intact. Though it doesn’t offer much nutritional value, it helps sweep the intestines, promoting bowel regularity and aiding toxin elimination through the stool.
Some dogs may instinctively consume grass when they need this cleansing effect, particularly after eating something heavy or indigestible.
In this way, grass acts almost like a natural brush for the intestines, helping move along waste products and excess mucus.
When to Be Concerned
Occasional grazing is completely normal, but persistent or frantic grass eating can signal an underlying issue such as:
Gastrointestinal irritation (IBS, gastritis, reflux)
Parasites (worms can irritate the gut lining)
Nutrient deficiencies (particularly minerals like magnesium or trace elements)
Boredom or anxiety leading to repetitive behaviour
If grass eating is accompanied by vomiting, diarrhoea, reduced appetite, or changes in behaviour, consult your vet or a canine nutrition professional.
A Note on Safety
Always ensure your dog’s chosen grass patch is free from pesticides, herbicides, and chemical fertilisers. These substances can be highly toxic, damaging the liver and nervous system even in small amounts.
Avoid roadside verges, public parks, and sprayed lawns. If you’d like to let your dog graze safely, you can even grow a pot of wheatgrass or barley grass indoors, it’s non-toxic and rich in chlorophyll.
More reading on grass eating can be found in the below links.
©️Kayleigh Adams, written for No Bull Just Natural Health For Dogs.
