Can Humans Get Sick From Eating Grass?

Over 3.5 million years ago, early hominins consumed a diet that included grass, but modern humans lack the necessary digestive system. While a lawn is not toxic, consuming it can lead to health problems due to indigestible cellulose, pesticides, and other contaminants.

Quick Summary

Humans can experience stomach upset, tooth damage, and other health issues from eating grass because their digestive system cannot break down cellulose effectively. Contaminants like pesticides also pose a significant risk, making the practice unsafe.

Key Points

• Indigestible Cellulose: Humans lack the cellulase enzyme needed to break down the fibrous cellulose in grass, meaning it passes through the body undigested.

• Digestive Upset: Eating grass can cause bloating, gas, diarrhea, and stomach pain because the human body cannot properly process its tough fibers.

• Harmful Contaminants: Lawn grass is often treated with toxic pesticides and herbicides, and can be contaminated with animal waste carrying pathogens like E. coli.

• Dental Damage: The high silica content in grass acts as an abrasive, wearing down tooth enamel over time, a problem herbivores avoid with specialized teeth.

• No Nutritional Benefit: Despite containing some nutrients, these are locked within indigestible cell walls, so eating grass provides no real energy or vitamins for humans.

• Evolved for a Varied Diet: The human digestive tract is shorter and less complex than that of herbivores, optimized for a varied, omnivorous diet rather than fibrous plants.

Why the Human Digestive System Fails to Process Grass

At the core of the issue is a fundamental difference in digestive biology between humans and dedicated herbivores like cows. The primary component of grass is cellulose, a complex carbohydrate that forms the rigid cell walls of plants. While humans can digest other carbohydrates like starch, we lack the specific enzyme, called cellulase, required to break the chemical bonds in cellulose. This makes grass largely indigestible for us, passing through our system with virtually no nutritional benefit. In contrast, ruminant animals such as cows, goats, and sheep have specialized multi-chambered stomachs and host symbiotic bacteria in their guts that produce cellulase, allowing them to extract nutrients from tough plant matter.

The Role of Cellulose and Lignin

Beyond simple cellulose, grass also contains a tough, woody polymer called lignin. Lignin is particularly problematic for the human digestive system. In high concentrations, it can inhibit the digestion of other fibers and nutrients. While some gut bacteria in humans can partially break down lignin, the process is not efficient enough to liberate significant nutrients. This combination of undigestible cellulose and difficult-to-process lignin means that eating lawn grass is not only pointless from a nutritional standpoint but can also cause considerable digestive distress.

Comparing Digestive Systems: Human vs. Herbivore

Feature	Human Digestive System	Herbivore (Ruminant) Digestive System
Stomach Type	Single-chambered (monogastric)	Multi-chambered (rumen, reticulum, omasum, abomasum)
Cellulose Digestion	Cannot digest; lacks cellulase enzyme	Specialized gut bacteria produce cellulase
Intestinal Length	Relatively short	Long to maximize nutrient absorption from fibrous plants
Chewing Action	Primarily vertical jaw movement	Side-to-side jaw motion for grinding tough fibers
Teeth	Enamel is susceptible to abrasion	Specialized, continuously growing teeth to resist abrasion from silica
Nutrient Absorption	Efficient for varied, omnivorous diet	Inefficient; requires large quantities and specialized processes

Immediate and Long-Term Health Risks of Eating Grass

Eating grass can pose a variety of health risks, from immediate gastrointestinal problems to long-term dental damage and exposure to harmful chemicals.

• Gastrointestinal Distress: Because humans cannot break down cellulose, eating a significant amount of grass will often result in digestive upset. Symptoms can include bloating, gas, stomach ache, diarrhea, or even vomiting as the body attempts to expel the indigestible fiber. In some cases, a large mass of fibrous material could potentially lead to intestinal blockage.

• Tooth Damage: Grass blades, especially tougher types like fescue, contain silica. Silica is an abrasive compound, essentially tiny rock particles, which can rapidly wear down tooth enamel. Unlike grazing animals whose teeth are adapted to continually grow, humans' teeth are not built for such an abrasive diet, and the damage can be permanent.

• Exposure to Pesticides and Herbicides: Most lawns and fields are treated with a variety of chemicals to control pests and weeds. Ingesting these pesticides and herbicides, which are toxic to humans, can cause severe illness, including cancer and birth defects over long-term exposure. The danger is magnified for children, whose smaller bodies are more susceptible to chemical toxins.

• Contamination from Waste and Pathogens: Grass that grows in public areas or yards is often contaminated with animal feces from pets, birds, and other wildlife. This waste can carry harmful bacteria like E. coli or parasites that can lead to infections and food poisoning. Furthermore, the grass itself can harbor various other environmental pathogens that are not meant for human consumption.

• Minimal Nutritional Value: While some grasses like wheatgrass are sold as health food supplements, the typical lawn grass offers no meaningful nutritional benefit to humans. The body expels it as insoluble fiber, meaning there are no usable calories, proteins, or vitamins to be gained. This can lead to starvation and malnutrition if consumed in large enough quantities in place of proper food.

Conclusion

While a single, accidental taste of lawn grass is unlikely to be fatal, the combination of indigestible fiber, abrasive silica, and potential chemical or biological contaminants makes eating grass a dangerous and fruitless endeavor for humans. Our digestive system is simply not equipped to process the cellulose and lignin found in grass, a biological limitation that differentiates us from herbivores. The risks of gastrointestinal distress, dental damage, and exposure to harmful toxins far outweigh any perceived benefit. For nutrition, humans should stick to a balanced diet of fruits, vegetables, grains, and proteins that their bodies are designed to digest.

Frequently Asked Questions

Why can't humans digest grass?

Humans cannot digest grass because they lack the specific enzyme, cellulase, that is required to break down cellulose, the primary component of grass's tough cell walls.

Is eating grass poisonous or toxic to humans?

The grass itself is not inherently poisonous, but it is impractical and can cause sickness due to chemical contamination from pesticides and herbicides, as well as biological contamination from animal waste.

What happens to your stomach if you eat grass?

If you eat grass, your stomach and intestines will struggle to process the indigestible fiber. This often leads to gas, bloating, stomach upset, and diarrhea as the body tries to expel the material.

Can eating grass lead to tooth damage?

Yes, grass contains an abrasive substance called silica, which can wear down the enamel on human teeth over time. Unlike herbivores, human teeth do not continuously regrow to compensate for this wear.

Do humans get any nutrients from eating grass?

No, humans get virtually no nutritional value from eating raw grass. The nutrients are locked within the indigestible cellulose, so the grass simply passes through the digestive system as insoluble fiber.

Why do animals like cows eat grass but humans can't?

Animals like cows are ruminants with a specialized, multi-chambered stomach and gut bacteria that produce cellulase, allowing them to ferment and break down grass efficiently. Humans lack this specialized digestive system.

What is the risk of food poisoning from eating grass?

The risk of food poisoning is high because outdoor grass can be contaminated with pathogens from animal feces, like E. coli and other bacteria, which can cause severe illness if ingested.