The Biological Problem: Why We Can't Digest Cellulose
The primary reason humans cannot eat and derive nutrition from common grass is a fundamental difference in our digestive systems compared to herbivores like cows and sheep. The cell walls of grass and other fibrous plants are made of a complex carbohydrate called cellulose. While cellulose is a type of fiber, our bodies lack the enzyme called cellulase, which is required to break down the strong chemical bonds in this molecule and convert it into digestible sugars.
Herbivores, or ruminant animals, have evolved to overcome this challenge. They have multi-chambered stomachs and a symbiotic relationship with specialized bacteria in their gut that produce cellulase. These animals can ferment the grass in their digestive tracts, breaking down the cellulose and extracting energy from it. Humans, with our single-chambered stomach, do not have this capability.
Comparing Digestive Systems
The table below highlights the key differences between how humans and ruminants process plant matter:
| Feature | Human Digestion | Ruminant (e.g., Cow) Digestion |
|---|---|---|
| Stomach Type | Single-chambered | Four-chambered (rumen, reticulum, omasum, abomasum) |
| Cellulase Enzyme | Absent | Produced by symbiotic bacteria in the rumen |
| Digestion Process | Relies on enzymes like amylase for starches; cellulose passes largely undigested | Fermentation process in rumen breaks down cellulose |
| Teeth | Not adapted for continuous grinding of abrasive plant matter | Continually growing teeth adapted to resist abrasion from silica |
| Nutrient Absorption | Efficiently absorbs nutrients from starches, proteins, and fats | Efficiently absorbs nutrients extracted from fermented grass by bacteria |
Significant Health Risks of Eating Grass
Beyond the lack of nutritional benefit, there are several serious health risks associated with consuming lawn grass or other common grasses. These dangers make it a profoundly bad idea to treat your lawn as a food source.
- Pesticide and Herbicide Exposure: Most residential and public lawns are treated with a cocktail of chemical pesticides, herbicides, and fertilizers. Ingesting these substances can lead to poisoning, causing a range of symptoms from mild irritation to severe, long-term health problems.
- Bacterial and Parasitic Contamination: Outdoor grass is frequently exposed to animal waste, including feces from dogs, birds, and other animals. This waste can carry harmful bacteria and parasites, which can lead to serious illnesses if ingested.
- Dental Damage: Grass contains a high amount of silica, a substance found in sand and rocks, which is highly abrasive. Chewing grass would act like sandpaper on your teeth, rapidly wearing down your enamel and causing permanent dental damage.
- Inadequate Calories and Starvation: Even if you were to process grass for some nutritional benefit, the energy required to chew and digest it would far outweigh the minimal calories you might gain. A diet consisting primarily of grass would lead to malnutrition and eventually starvation.
- Potential Toxicity: While many grasses are technically non-toxic, some types contain compounds that can be harmful when consumed in large quantities. For instance, some grasses, like Johnson grass, can produce cyanide during the digestive process.
Not All Grasses Are Created Equal: The Exception of Grains
It is important to differentiate between the grass on your lawn and the many members of the grass family (Poaceae) that are staples of the human diet. These edible forms of grass are cultivated specifically for human consumption, and we consume different parts of the plant.
Common edible grasses (cereals and grains) include:
- Wheat: The seeds (grains) are milled into flour for bread and pasta.
- Rice: The seeds of the rice plant are a dietary cornerstone for billions.
- Corn: A domesticated grass grown for its seeds, which we consume in various forms.
- Oats and Barley: Cereal grains used in porridge, baking, and other foods.
- Wheatgrass and Barley Grass: These are the shoots of young cereal grasses, typically consumed juiced or powdered. This processing breaks down the fibrous cell walls, making the nutrients more available, though the fiber itself is still indigestible.
Processing vs. Chewing: Why Wheatgrass is Different
People sometimes point to wheatgrass shots as evidence that grass is edible. However, this is a flawed comparison. The nutritional benefits of wheatgrass are derived from juicing, a process that mechanically breaks down the tough cell walls and separates the nutrient-rich liquid from the indigestible fiber. You are not eating the fibrous grass itself, but drinking its extracted juice. The fiber, which would cause digestive distress, is discarded.
In contrast, simply chewing and swallowing your lawn grass, which is not cultivated for nutrition and often treated with chemicals, is a completely different, and dangerous, proposition. The abrasiveness of the grass and the indigestible bulk would irritate your digestive system and offer no meaningful benefit.
Conclusion: Stick to Your Salad
While the concept of eating grass might seem like a simple solution for sustenance, the biological realities make it a poor and dangerous choice for humans. Our bodies are not equipped to handle the high cellulose content, and we lack the specialized digestive system of true herbivores. The potential for ingesting harmful chemicals and the risk of damaging your teeth far outweigh any perceived benefit. For greens, humans have a wide variety of safe, nutritious, and delicious options cultivated over millennia. It is always best to stick to foods designed for our consumption rather than attempting to graze your way to a meal. For more information on why humans and ruminants digest differently, see this article from the FDA on how cows eat grass.
