Is There Nutritional Value in Eating Grass?

According to ancient findings published in the Proceedings of the National Academy of Sciences, our ancestors once consumed grass, but today's common lawn grass holds virtually no nutritional value for humans. So, is there nutritional value in eating grass? The short answer is no, due to our unique digestive system and the high cellulose content of grass.

Quick Summary

This article explores why humans cannot derive nutrition from eating grass, focusing on the roles of cellulose, the lack of specific enzymes, and the differences between human and herbivore digestive systems. It also details the risks of consuming grass and distinguishes between regular lawn grass and edible cereal grasses.

Key Points

• Cellulose is Indigestible: The primary reason humans cannot derive nutritional value from common grass is the inability to digest cellulose, its main component, due to lacking the necessary enzyme, cellulase.

• Digestive Systems Differ: Unlike ruminants such as cows, humans have a single-chambered stomach and lack the symbiotic gut bacteria required to ferment and break down cellulose.

• Risks Outweigh Benefits: Consuming lawn grass can cause digestive distress like bloating and diarrhea, lead to severe tooth wear from high silica content, and risk exposure to pesticides and parasites.

• Not a Survival Food: In a survival scenario, eating grass provides negligible energy and nutrients and is not a sustainable solution for human health.

• Cereal Grasses Are Different: Edible cereal grasses like wheatgrass are consumed in processed forms (juices, powders) and provide concentrated nutrients; they are not comparable to chewing raw lawn grass.

• Focus on a Varied Diet: For optimal health, a varied diet of fruits, vegetables, grains, and other suitable foods is essential, as the human digestive system is uniquely adapted for such diversity.

The Core Problem: Indigestible Cellulose

The primary reason humans cannot get any nutritional value from eating common grass is the high concentration of cellulose. Cellulose is a complex carbohydrate that forms the rigid cell walls of plants. While it is a form of sugar, the glucose units are linked together by beta-glycosidic bonds, which the human digestive system lacks the enzymes to break down. The specific enzyme needed, cellulase, is absent in humans.

The Human Digestive System vs. Ruminant Digestion

To understand why we can't eat grass, it helps to compare our digestive tract to that of a ruminant animal like a cow. The difference is stark, and it perfectly illustrates our biological limitations.

The Human Digestive System:

• A simple, single-chambered stomach.
• A relatively short intestinal tract.
• Relies on enzymes like amylase, protease, and lipase to break down starches, proteins, and fats.
• Lacks the cellulase enzyme needed for cellulose digestion.
• Processes cellulose as insoluble fiber (roughage) that adds bulk to stool but provides no energy.

The Ruminant Digestive System (e.g., Cows, Sheep):

• A multi-chambered stomach, including the rumen.
• The rumen houses trillions of symbiotic bacteria and microbes.
• These microbes produce cellulase to break down cellulose through fermentation.
• Ruminants regurgitate and re-chew their cud to further process the tough plant fibers.
• Absorbs nutrients, primarily volatile fatty acids, that are byproducts of microbial fermentation.

The Health Risks of Eating Grass

Beyond the lack of nutrition, consuming common lawn grass can pose several health risks for humans. It is not an effective survival tactic and can lead to serious health problems.

• Digestive Distress: Attempting to eat large quantities of grass can lead to digestive issues such as bloating, gas, stomach cramps, and diarrhea, as the undigested fibrous material irritates the digestive tract.
• Tooth Wear: Grass contains a high amount of silica, a hard, abrasive compound that can cause significant wear and tear on human tooth enamel over time. Grazing animals have teeth that are adapted to this constant abrasion, but human teeth are not.
• Exposure to Chemicals and Parasites: Lawn grass is often treated with pesticides, herbicides, and other chemicals that are toxic to humans. It can also harbor bacteria, fungi, and parasites from animal waste, presenting a risk of illness.
• Nutrient Deficiency: Relying on grass for nutrition would inevitably lead to severe deficiencies in essential proteins, fats, and vitamins, potentially causing malnutrition and starvation.

Common Grass vs. Edible Grasses

It's important to differentiate between common lawn grass and edible cereal grasses, which are commonly found in supplements like wheatgrass and barley grass powders. While both are members of the same family, their uses and nutritional availability are completely different.

Feature	Common Lawn Grass (e.g., Kentucky Bluegrass)	Edible Cereal Grasses (e.g., Wheatgrass, Barley Grass)
Digestibility	Highly indigestible for humans due to high cellulose content.	Processed into powders, juices, and supplements, making their nutrients accessible.
Nutrient Availability	Locked within cellulose walls; provides zero meaningful nutrition to humans.	Concentrated source of vitamins (A, C), minerals, antioxidants, and amino acids.
Consumption Method	Not meant for human consumption.	Consumed as a juice shot or added to smoothies/supplements, not eaten raw.
Cellulose Content	High. Acts as roughage, passing through the system mostly unchanged.	Significantly lower in processed forms, and not consumed in large, unprocessed quantities.
Growth Stage	Mature, fibrous leaves.	Harvested at an early, vegetative stage for peak nutrient density.

Conclusion

While a cow's ability to thrive on a diet of grass might make it seem like a viable food source, it is not for humans. Our digestive biology, which lacks the enzyme cellulase, makes it impossible to extract any meaningful nutrition from the abundant cellulose in grass. Attempting to do so can lead to health problems ranging from digestive upset to dental issues caused by abrasive silica. While edible cereal grasses like wheatgrass and barley grass offer real health benefits in their concentrated, processed forms, eating the grass from your lawn is a futile and potentially dangerous activity. For those looking for plant-based nutrition, a diverse diet of fruits, vegetables, and grains remains the optimal and safest path.

To learn more about the differences in dietary needs between humans and other animals, consult reputable biological and nutritional resources.

Optional Outbound Link: For more information on the intricate science of human digestion, explore the educational resources from the National Institute of Diabetes and Digestive and Kidney Diseases.

Frequently Asked Questions

Why can't humans digest grass?

Humans cannot digest grass primarily because we lack the enzyme cellulase, which is required to break down cellulose, the tough carbohydrate that forms the cell walls of grass.

Can eating grass make a human sick?

Yes, eating grass can cause health issues, including digestive upset such as bloating and diarrhea, dental damage from abrasive silica, and illness from pesticides or parasites present on the grass.

Do herbivores have a different digestive system from humans?

Yes, herbivores like cows have specialized digestive systems, often with multiple stomach chambers (a rumen), that house symbiotic bacteria capable of fermenting and digesting cellulose.

Is wheatgrass the same as lawn grass?

While both are grasses, they are harvested and consumed differently. Wheatgrass is harvested young and processed into juice or powder to make its high nutrient content accessible. Common lawn grass is fibrous and indigestible.

What happens if a human eats a large amount of grass?

Consuming a large amount of grass will likely result in gastrointestinal distress, as the indigestible cellulose passes through the system largely unchanged. In extreme cases, it can cause blockage or damage to the intestinal tract.

Does grass have any beneficial nutrients for humans at all?

Common grass provides no beneficial nutrients to humans in its raw form. The high cellulose content locks away any vitamins or minerals, making them unavailable to our digestive system.

What is cellulose and why is it indigestible for humans?

Cellulose is a complex carbohydrate that provides structural support for plants. Humans can't digest it because our bodies lack the specific enzymes to break its beta-glycosidic bonds, causing it to pass through as insoluble fiber.