What would happen if I only ate grass?

November 23, 2025 •

4 min read

While it may seem abundant, around 30% of a plant's cell wall is made of cellulose, which humans cannot digest efficiently. A diet consisting exclusively of grass would lead to significant health complications, not sustained nourishment. This article explores the drastic and dangerous consequences of what would happen if I only ate grass.

Quick Summary

This article examines the consequences of an all-grass diet for humans, outlining the severe health risks, including malnutrition, digestive upset, and dental damage, that would occur due to our biological inability to properly digest and extract nutrients from grass.

Key Points

Indigestible Cellulose: Humans lack the enzyme cellulase needed to break down cellulose, the primary component of grass, meaning we cannot extract energy from it.
Severe Malnutrition: An exclusively grass diet would lead to starvation, as it provides almost no usable calories, proteins, or essential fats for human consumption.
Digestive Distress: The high fiber content would cause significant digestive upset, including bloating, cramps, diarrhea, and vomiting.
Dental Erosion: The abrasive silica in grass would wear down tooth enamel over time, causing irreversible dental damage.
Contamination Risk: Lawn and field grasses can contain toxic pesticides, herbicides, and other pollutants, posing a poisoning risk.
Evolutionary Difference: Unlike ruminants with complex digestive systems and gut bacteria, our single-chambered stomach is unsuited for a grass-based diet.
Human Diet is Varied: Our diet evolved to rely on nutrient-dense foods, a stark contrast to the low-yield energy source of grass.

Your Digestive System is Not Designed for Grass

One of the most critical reasons humans cannot survive on grass is our digestive system's fundamental architecture. Unlike herbivores, such as cows and sheep, humans do not possess the necessary enzymes or the complex, multi-chambered stomach required to break down cellulose effectively. The digestive systems of ruminant animals host symbiotic bacteria that produce the enzyme cellulase, which breaks down the fibrous cellulose into digestible sugars. Our single-chambered stomach and shorter intestinal tract are optimized for an omnivorous diet, which includes easily digestible carbohydrates, proteins, and fats.

The Indigestible Role of Cellulose

Grass is predominantly composed of water and cellulose, a complex carbohydrate that provides the plant with its structural rigidity. For humans, cellulose functions as insoluble dietary fiber, which, while beneficial in small amounts for promoting bowel movements, passes through the digestive tract largely undigested and provides no energy. When you eat grass, the vital nutrients locked within the plant cells remain inaccessible, making it impossible to meet your body's caloric needs. Instead, you would be ingesting a large amount of indigestible fiber, which would lead to severe digestive distress.

Serious Health Consequences of a Grass-Only Diet

Attempting to subsist on grass would trigger a cascade of dangerous health problems. The immediate issues would involve the digestive tract, but the long-term effects of severe malnutrition are far more concerning.

Acute Digestive Issues: Consuming large quantities of fibrous, indigestible grass would cause severe digestive upset. Symptoms would likely include intense stomach cramps, bloating, excessive gas, and persistent diarrhea or vomiting. The body would struggle to process the tough plant matter, leading to irritation and inflammation of the gut lining.
Severe Malnutrition and Starvation: Despite potentially feeling full, your body would be receiving almost zero usable nutrients from the grass. This would quickly lead to malnutrition, as you would lack essential proteins, fats, and critical vitamins and minerals necessary for survival. Your body would begin to break down its own muscle and fat stores for energy, leading to extreme weight loss and organ damage.
Dental Damage: Grass contains high levels of silica, the same abrasive mineral found in sand and rock. Chewing this tough, abrasive material would cause significant and rapid wear and tear on your teeth, eroding the enamel. While herbivores like cows have constantly growing teeth to counteract this effect, human teeth are not designed to withstand such damage.
Potential for Toxicity: Many common lawn grasses are treated with pesticides, herbicides, and fertilizers that are highly toxic to humans. Consuming these contaminated plants would introduce dangerous chemicals into your body, potentially causing a range of serious health issues, including liver and kidney damage, and could even be fatal.

Comparison of Human vs. Ruminant Digestion


Feature	Humans (Omnivore)	Ruminants (Herbivore, e.g., Cows)
Stomach Chambers	Single-chambered stomach	Multi-chambered stomach (e.g., four chambers)
Cellulase Enzyme	Absent; cannot produce cellulase	Produced by symbiotic gut bacteria
Digestion Process	Relies on enzymes like amylase, protease, lipase to break down easily accessible nutrients.	Utilizes fermentation in specialized stomach chambers (rumen) to break down cellulose with bacterial assistance.
Chewing Method	Chewing facilitates initial breakdown, but no further fermentation of cellulose occurs.	Chews cud (regurgitated, partially digested grass) to further break down fibers for fermentation.
Nutrient Extraction	Extracts nutrients from fruits, grains, vegetables, and meat; cellulose is undigested fiber.	Bacteria break down cellulose into usable fatty acids that the animal can absorb for energy.

The Evolutionary Reason for Our Diet

Our evolutionary path diverged significantly from that of strict herbivores millions of years ago. The development of tools, fire, and a reliance on a varied diet, including cooked foods, allowed our ancestors to extract more nutrients from food with less effort. This shift in diet is believed to have contributed to the development of our larger brains and shorter digestive tracts, as the energy-intensive process of digesting fibrous plants was no longer the primary focus. Essentially, our bodies adapted to a more nutrient-dense diet, leaving behind the need for the specialized digestive systems seen in grazing animals.

Conclusion: A Dangerous and Ineffective Strategy

While the thought of an unlimited food source like grass may seem appealing in a survival scenario, the biological reality for humans is grim. An exclusively grass-based diet would be a starvation diet, leading to severe malnutrition, painful digestive problems, and irreversible dental damage. Unlike grazing animals that have evolved specialized digestive systems and symbiotic bacteria to break down cellulose, our bodies are simply not equipped for the task. The high silica content and potential for contamination further compound the health risks. The best approach for human health is to stick to a varied and balanced omnivorous diet that provides all the necessary nutrients for survival and well-being.

You may be surprised to learn that humans do consume some types of grass family products every day, such as grains like wheat, rice, and corn, but these are highly processed seeds or cultivated varieties, not the fibrous blades of your lawn.

Lists

Short-term effects of eating grass: Digestive distress, stomach cramps, bloating, gas, diarrhea, vomiting.
Long-term effects of eating grass: Severe malnutrition, muscle and fat loss, dental enamel erosion, potential toxicity from pesticides.
What humans lack for digesting grass: The enzyme cellulase, specialized gut bacteria, and a multi-chambered stomach.
Why grass is not a viable food source for humans: Minimal nutritional value, high cellulose content, presence of abrasive silica, and potential for toxic chemical contamination.
How ruminants digest grass: Chewing cud, fermentation in the rumen by bacteria, and a multi-chambered stomach.

Frequently Asked Questions

Cows are ruminants with a specialized, multi-chambered stomach and a symbiotic relationship with gut bacteria that produce the enzyme cellulase. This allows them to ferment and break down the cellulose in grass, a process humans cannot replicate.

For humans, grass has virtually no nutritional value. While it contains some vitamins and minerals, they are locked within the indigestible cellulose cell walls, and our bodies cannot access them.

Eating too much grass would likely cause acute digestive issues, including stomach cramps, bloating, gas, and either vomiting or diarrhea, as the body attempts to expel the indigestible fibrous material.

No, you would not survive long on grass. While it might temporarily fill your stomach, it provides no energy and would lead to eventual starvation. Survivalists prioritize calorie-dense foods, which grass is not.

Wheatgrass juice is digestible because the tough cellulose fiber is removed during juicing, leaving behind the nutrient-rich liquid. However, this is different from eating solid grass blades, which are indigestible.

The fiber in grass is the same cellulose found in other plant-based foods, but its high concentration and tough structure make it difficult for our digestive system. While fiber is beneficial, the disproportionate amount in grass is not ideal and offers no caloric benefit.

Yes, you would eventually die from malnutrition and starvation if you only ate grass. Without a source of usable calories, protein, and fat, your body would enter a state of severe nutrient deficiency, leading to organ failure and death.