Does grass give energy?

December 21, 2025 •

3 min read

While cows and other grazing animals can survive entirely on grass, humans cannot extract any meaningful energy from it due to our unique digestive systems. This fundamental biological difference means the answer to the question, "Does grass give energy?" depends entirely on the species in question and the method of processing.

Quick Summary

Humans cannot obtain energy from eating grass due to lacking the necessary enzymes and digestive structure to break down cellulose. Conversely, herbivores use symbiotic bacteria in their specialized digestive tracts to ferment grass into usable energy. Furthermore, grass can be a significant source of energy through modern biofuel and biogas production.

Key Points

Human Inability: Humans cannot get meaningful energy from grass because our digestive system lacks the enzyme cellulase to break down its tough cellulose fibers.
Herbivore Specialization: Herbivores like cows rely on symbiotic microorganisms in their multi-chambered stomachs (rumen) to ferment grass into usable volatile fatty acids for energy.
Biofuel Potential: Grass is a promising renewable energy source, converted into biomass pellets for combustion or used in anaerobic digestion to produce methane-rich biogas.
Dietary Role: For humans, the most important contribution of the grass family is through the consumption of its seeds, which are the grains (wheat, rice, corn) that form a staple part of our diet.
Energy Inefficiency: Even for animals that can digest it, grass is a low-energy density food, requiring herbivores to eat large quantities for most of their waking hours to survive.

The Fundamental Difference: Humans vs. Herbivores

At the core of the issue lies a carbohydrate called cellulose, a tough, fibrous material that makes up the cell walls of plants. For humans, cellulose passes through our digestive tract mostly undigested, functioning only as a form of dietary fiber that aids in the movement of food. We lack the enzyme, cellulase, which is required to break down cellulose into the simple sugars our bodies use for energy. This is in stark contrast to herbivores.

How Herbivores Extract Energy from Grass

Animals like cows, sheep, and goats, known as ruminants, have evolved a complex digestive system perfectly suited for a grass-based diet. Their stomachs are multi-chambered, with the rumen acting as a large fermentation vat where billions of symbiotic microbes reside. These microorganisms are the key, as they produce the cellulase enzyme needed to digest cellulose.

The process begins when the herbivore chews and swallows the grass, sending it to the rumen.
The microbial community then begins the slow process of fermentation, breaking down the tough plant fibers.
The herbivore will later regurgitate and re-chew the material, known as cud, to further aid in the breakdown.
The microbes convert the cellulose into volatile fatty acids (VFAs), which the animal's body can absorb as its primary energy source.
Because grass has relatively low energy density, herbivores must spend a significant portion of their day eating large quantities to meet their nutritional needs.

Modern Applications: Grass as a Biofuel

While not suitable as a direct energy source for human consumption, grass has a promising future in renewable energy. The energy-rich biomass of grasses can be harvested and processed to create sustainable fuel sources.

Biomass Combustion: Certain perennial grasses, like Miscanthus x giganteus and switchgrass, are grown specifically as energy crops. Once harvested and dried, these grasses can be baled and burned in specialized power plants to generate heat or electricity. The process is considered carbon-neutral because the carbon dioxide released during combustion was initially captured by the grass as it grew.
Anaerobic Digestion: A process similar to the fermentation in a cow's stomach, anaerobic digestion involves placing organic material like grass cuttings into a sealed tank. Microorganisms then break down the material in the absence of oxygen, producing biogas (primarily methane) and a nutrient-rich byproduct called digestate. The biogas can be used for heat, electricity, or as a natural gas substitute.

Other Ways Humans Consume Grass-Family Plants

It's important to remember that not all plants in the grass family (Poaceae) are indigestible for humans. In fact, many are cornerstones of our diet. Humans primarily consume the seeds of these grasses, which are far more nutrient-dense and lack the tough cellulose structure of the blades.

Cereal Grains: Common grains like wheat, rice, corn, oats, and barley are all members of the grass family. For centuries, humans have cultivated and consumed the energy-rich seeds of these grasses.
Culinary Herbs: Some grass varieties are used for flavor, such as lemongrass in many Asian cuisines. While the leaves are used, they are not consumed for energy.
Wheatgrass Juice: Some people consume wheatgrass in a juiced form. This process removes the fibrous cellulose, allowing the body to absorb the sugars, vitamins, and minerals. However, the nutritional output is modest compared to other foods.

Comparison Table: Human vs. Herbivore Digestion


Feature	Humans	Herbivores (Ruminants like Cows)
Primary Diet	Omnivorous (diverse)	Herbivorous (specialized in plants)
Key Enzyme for Cellulose	Absent (No cellulase)	Present (Produced by symbiotic microbes)
Digestive System	Simple, single-chambered stomach	Complex, multi-chambered stomach (e.g., rumen)
Ability to Absorb Energy from Grass Blades	Negligible	High, via fermentation
Energy Acquisition	Fast, high-energy foods	Slow, low-energy density foods

Conclusion

So, does grass give energy? For humans, the answer is a definitive no, at least not directly from the blades of your lawn. Our physiology lacks the specialized tools to break down the tough cellulose fibers that contain energy. However, for herbivores equipped with symbiotic gut bacteria and a multi-chambered stomach, grass is their main energy source. In a broader, modern context, grass offers significant energy potential as a renewable biofuel, processed into pellets or biogas. Ultimately, whether grass provides energy is a matter of both biological and industrial capability, not inherent nutritional content. While we shouldn't start grazing, we can certainly appreciate the role of grasses in sustaining life and powering our world in a cleaner way. To learn more about the role of grasses as a biofuel source, consider reviewing resources like the Open University's biofuel sections.

Frequently Asked Questions

Humans are unable to digest the cellulose in grass because we do not have the necessary enzyme, cellulase, or the specialized digestive tract found in herbivores that can break down this complex carbohydrate.

Cows, as ruminants, have a specialized four-chambered stomach. In the first chamber, the rumen, symbiotic bacteria and other microbes ferment the cellulose in grass, converting it into volatile fatty acids that the cow's body can absorb and use for energy.

Yes, certain types of fast-growing grasses like switchgrass can be cultivated as energy crops. The harvested grass biomass can be burned for heat and electricity or processed through anaerobic digestion to produce biogas.

Wheatgrass juice is different from eating grass directly. When wheatgrass is juiced, the fibrous, indigestible cellulose is removed, leaving behind the liquid containing sugars, vitamins, and minerals that our bodies can absorb.

If a human eats grass, it will pass through the digestive system mostly undigested. It provides no significant nutritional energy, and consuming large amounts could lead to digestive upset. The silica in grass is also very abrasive and can damage human teeth.

Yes, humans consume many plants from the grass family, including the seeds of cereals like wheat, rice, and corn. Other examples include bamboo shoots and culinary grasses like lemongrass.

Grass does contain some nutrients like vitamins and minerals, but for humans, they are locked within the indigestible cellulose fibers. Juicing can extract some of these, but eating the blades whole provides no practical nutritional benefit.