Is it safe for humans to eat grass?

January 9, 2026 •

4 min read

According to research on ancient human diets, our ancestors once included grasses, but modern human physiology is fundamentally unsuited for consuming grass blades. So, is it safe for humans to eat grass? The scientific consensus points to significant health risks and minimal nutritional gain, making it an inadvisable food source for humans.

Quick Summary

Humans lack the necessary enzymes to break down cellulose in grass, making it indigestible and nutritionally worthless. Consumption can lead to digestive distress, dental damage, and potential exposure to pesticides or parasites.

Key Points

Indigestible Cellulose: Humans lack the cellulase enzyme needed to break down grass fiber, making it nutritionally useless.
Significant Health Risks: Eating grass exposes humans to pesticides, herbicides, parasites, and pathogens from animal waste.
Dental Damage: The high silica content in grass is abrasive and can cause long-term wear and tear on human tooth enamel.
Malnutrition and Starvation: Relying on grass as a food source would lead to severe nutrient deficiencies and starvation due to lack of caloric energy.
Toxic Grass Varieties: Some specific types of grass can be acutely poisonous, containing naturally occurring toxins like cyanide.
Herbivore vs. Human Digestion: Grazing animals like cows have multi-chambered stomachs and specialized bacteria to ferment grass, unlike humans.
Edible Grasses Are Different: Common grains (seeds) and juiced wheatgrass are not the same as fibrous grass blades and are processed differently by the body.

The Core Biological Barrier: Cellulose and Digestion

At the heart of the issue is the structure of grass and the human digestive system. The main component of grass is cellulose, a complex carbohydrate that provides its rigid cell walls. While cellulose is a type of dietary fiber, the human body lacks the enzyme called cellulase, which is necessary to break down its beta-glycosidic bonds into digestible sugars.

The Problem with Indigestible Cellulose

Since humans cannot produce cellulase, the vast majority of grass fiber passes through our digestive tract largely undigested. This means it provides no caloric energy or meaningful nutrient absorption. While it can add bulk to stool as insoluble fiber, a diet based on grass would lead to severe malnutrition and starvation, as seen in times of famine. Our digestive system is simply not equipped to extract the nutrients locked within the tough plant fibers.

The Ruminant Advantage: Why Cows Can Eat Grass

Herbivores like cows and sheep can thrive on a grass-based diet due to specialized biological adaptations. Unlike the human monogastric (single-chambered) stomach, ruminants possess a multi-chambered stomach.

This digestive marvel works as follows:

Rumen: The first and largest chamber, housing billions of symbiotic microorganisms (bacteria and protozoa) that produce cellulase.
Rumination: Ruminants regurgitate their food (cud) to re-chew it, further breaking down the fibrous plant material.
Fermentation: The microorganisms in the rumen ferment the cellulose, breaking it down into volatile fatty acids that the animal can absorb for energy.

These processes are completely absent in the human digestive system, highlighting the fundamental differences that make grass an unsuitable food source for us.

Significant Health Risks Associated with Eating Grass

Beyond the lack of nutrition, attempting to consume grass poses several direct health risks for humans.

Key risks include:

Exposure to Pesticides and Herbicides: Many residential lawns and public green spaces are treated with chemical pesticides, herbicides, and fertilizers. Ingesting grass from these areas could lead to chemical poisoning.
Ingestion of Parasites and Pathogens: Grass can be contaminated with bacteria, mold, or parasites from animal feces (pets, wildlife). These pathogens can cause severe gastrointestinal illness in humans.
Dental Damage from Silica: Grass contains high levels of silica, a naturally abrasive mineral. Chewing large quantities of grass would rapidly wear down tooth enamel, potentially leading to long-term dental problems.
Toxic Varieties: Certain types of grass contain naturally occurring toxins. For example, Johnson grass and some ornamental grasses can produce toxic compounds, such as cyanide, when stressed or consumed.
Digestive Upset: The human body's inability to digest the high fiber and lignin content can cause stomach cramps, bloating, nausea, vomiting, and diarrhea.

Comparison of Human vs. Herbivore Digestive Systems


Feature	Human Digestive System	Herbivore Digestive System (e.g., Cow)
Stomach Chambers	Monogastric (Single-chambered)	Multi-chambered (Rumen, Reticulum, Omasum, Abomasum)
Cellulose Digestion	Lacks cellulase enzyme; passes largely undigested	Specialized gut bacteria produce cellulase
Nutrient Extraction	Cannot extract energy from grass fiber	Fermentation by microbes releases volatile fatty acids for energy
Teeth	Omnivorous teeth; easily abraded by grass silica	Adapted for continuous chewing; grow to compensate for wear
Intestine Length	Relatively short intestinal tract compared to herbivores	Long, complex digestive tract for maximum extraction
Dietary Specialization	Omnivorous; relies on varied food sources	Herbivorous; adapted specifically for plants

Understanding 'Edible' Grasses

It's important to distinguish between fibrous grass blades and other members of the grass family that are staples in the human diet. Cereal grains like wheat, rice, corn, and oats are the seeds of grass species, not the blades. These seeds have been selectively bred over millennia to be digestible and nutritious for humans. Similarly, the popular health supplement wheatgrass is consumed as a juice, allowing humans to absorb some of the nutrients without having to process the indigestible fiber. This is a fundamentally different process from eating the raw, fibrous blades of lawn grass.

Conclusion: Best to Leave the Lawn for Grazers

Ultimately, the scientific consensus is clear: it is not safe or beneficial for humans to eat grass blades. Our digestive system, dental structure, and evolutionary history have not prepared us for such a diet. The risks of consuming pesticides, pathogens, and abrasive silica far outweigh the nonexistent nutritional rewards. For healthy, leafy green nutrients, it is best to stick with low-cellulose vegetables that our bodies are well-equipped to digest. The grass is, and should remain, the domain of grazing animals who possess the unique adaptations required to process it safely and effectively.

For more information on the complexities of human digestion, explore research on the differences between our system and herbivores like cows.

Frequently Asked Questions

No, humans cannot get meaningful nutrition from consuming grass blades. Our digestive system lacks the necessary enzymes to break down cellulose, the main fiber in grass, so it passes through largely undigested.

Herbivores like cows are ruminants with multi-chambered stomachs and specialized bacteria that produce the enzyme cellulase. This allows them to ferment and digest grass effectively to extract nutrients, a capability humans do not possess.

Eating a small amount of clean grass is unlikely to cause serious harm, but it offers no nutritional benefit. It may cause mild digestive upset, as the body cannot process the tough fibers.

Dangers include exposure to pesticides and herbicides used on lawns, ingestion of parasites or pathogens from animal waste, dental abrasion from the high silica content, and potential poisoning from certain naturally toxic grass varieties.

No, wheatgrass is the young blade of the wheat plant and is typically consumed as a juice. This process separates the digestible nutrients from the indigestible fiber, unlike eating fibrous lawn grass directly.

While it is technically non-toxic, eating regular lawn grass would not provide enough nutrients to sustain life and could lead to starvation. Furthermore, some specific grass types are inherently poisonous and could cause severe illness or death if ingested.

Yes, some early human ancestors included grasses in their diet, according to a study published in the Proceedings of the National Academy of Sciences. However, their dietary habits and digestive systems were different from modern humans.