Eating wood may seem like an odd concept, but you may be surprised to learn that humans can actually digest certain types of wood fiber to some extent. If you’ve ever wondered whether you could eat and digest parts of a tree or wood materials, read on for a deep dive on this unusual question.
The short answer is: humans can digest some types of wood fiber to a limited degree if consumed in small amounts, but our digestive systems are not well equipped to break down most wood components.
An Overview of Wood Composition
Wood is composed of several key components that give it unique properties. The primary building blocks are cellulose, lignin, hemicellulose, and extractives.
Cellulose
Cellulose is the most abundant organic polymer on Earth. It makes up 40-50% of wood by weight. The cellulose molecules bind together to form long chains and fibrous strands that provide the structural framework of plant cell walls.
Lignin
Lignin is a complex polymer that makes up 18-35% of wood by weight. It acts like a glue, binding the cellulose fibers together to provide rigidity and strength. Lignin is what makes wood so tough and dense.
Hemicellulose
Hemicellulose is another important component of plant cell walls. It accounts for 25-35% of wood composition. Hemicelluloses help crosslink the cellulose microfibrils to confer additional structural support.
Extractives
A variety of organic compounds like terpenes, fats, resins, and waxes are extracted from wood during the pulping process. These extractives make up 5-10% of wood. Although a relatively minor component, extractives contribute to wood’s color, odor, and decay resistance.
Human Digestion Capabilities and Limitations
Stomach Acid
The human stomach contains hydrochloric acid, which helps break down food during digestion. This strong acid kills bacteria and pathogens, and denatures proteins in preparation for further digestion (1). The pH of stomach acid is between 1.5 and 3.5, making it highly acidic.
This allows the stomach to break down foods even if we don’t chew them thoroughly beforehand. Pretty amazing, right? !
However, there are some limitations. Cellulose from plant fiber cannot be broken down by our stomach acid or digestive enzymes. While the acid can help break apart the plant matter, our bodies lack the enzymes needed to fully digest components of fiber like cellulose (2).
Enzymes That Break Down Fiber
Humans lack most of the enzymes needed to digest fiber and cellulose found in plant foods. We do produce small amounts of cellulase, but not enough to derive significant nutritional value from digesting most dietary fiber.
Herbivores like cows and termites produce large quantities of cellulase and can gain energy from digesting fiber-rich foods. We humans miss out on their superpowers when it comes to dismantling those crunchy veggies and fibrous fruits!
Our limited enzyme production means most of our dietary fiber passes through undigested (3).
Passage Rate Through Digestive Tract
It typically takes 24-72 hours for food to pass through the human digestive system, depending on the individual. Foods higher in fat, protein and fiber take longer to digest compared to foods high in sugars and carbohydrates (4).
For example, greasy pizza loaded with cheese and meats would likely take 50-65 hours to fully pass through your system. In contrast, a sugary cereal may only take 30 hours start to finish. The rate of digestion determines how much time the body has to absorb nutrients from food.
Nutrient Absorption
Although humans cannot directly digest fiber, it still provides health benefits. Fiber helps regulate digestion, promotes satiety, and feeds the good bacteria in our gut microbiome (5).
While we cannot absorb energy from fiber itself, fermentation of fiber by gut bacteria produces beneficial short-chain fatty acids that can be absorbed and provide energy. So in a roundabout way, fiber digestion ends up producing extra nutrients for us – not too shabby!
Types of Wood Humans Can Partially Digest
Softwoods vs. Hardwoods
When it comes to digesting wood, there is a difference between softwoods and hardwoods. Softwoods like pine, fir, and cedar actually contain small amounts of nutrients and can be partially broken down by the digestive system.
The cellulose and lignin that makes up wood is tough, but softwoods have less lignin, making them slightly more digestible.
Hardwoods like oak, maple, and mahogany contain more lignin and complex carbs that cannot be digested by the human gastrointestinal tract. While both types of wood should not actually be eaten, softwoods stand a better chance at being partially digested before they cause intestinal damage or blockages.
Wood Pulp/Cellulose Powders
Wood that has been processed into a pulp or powder is more digestible than solid wood. Wood pulp is made by removing the lignin from wood via chemical processing, leaving behind just the cellulose fibers. When in powder form, more of the cellulose can be dissolved and fermented in the gut.
That said, a 2018 study showed that the digestibility of wood pulp decreases as the consumption amount increases. So only a small amount of cellulose powder can actually be digested before side effects occur. Too much puts you at risk for intestinal issues.
Ispaghula Husk (Psyllium Husk)
Ispaghula husk, also known as psyllium husk, is a type of edible plant fiber derived from the Plantago ovata plant. It contains a large amount of soluble fiber that can absorb water and partially ferment when consumed. This gives it digestive benefits as a fiber supplement or laxative.
One study in the British Journal of Nutrition showed that around 50-60% of psyllium husk fiber is fermented in the colon, contributing useable calories to the body. So while it contains compounds found in some wood plants, psyllium husk is much more digestible than actual wood due to its soluble fiber content and processed form.
Potental Benefits and Risks of Ingesting Wood Fiber
Gut Health
Some research indicates that ingesting certain types of processed wood fiber may provide benefits for digestive and gut health. For example, studies show that wood-derived xylooligosaccharides (XOS) can act as prebiotics that stimulate the growth of beneficial bifidobacteria and lactobacilli in the intestines.
This may help reduce inflammation and enhance immunity.
Additionally, the fiber in wood can provide bulk to stools and promote regularity. One study found that supplemental wood fiber from Arctium lappa L. plant helped relieve constipation and support healthy bowel movements in subjects with digestion issues.
Weight Management
Some research has explored the potential for wood fiber to assist with weight loss and fat burning. For example, cellulose from wood pulp has been shown to decrease fat digestion and absorption. This may help promote feelings of fullness and appetite control.
Additionally, the prebiotic XOS found in wood materials may enhance satiety hormones, according to some studies. This could aid weight management in overweight individuals when combined with dietary changes.
| Study | Key Findings on Wood Fiber and Weight Loss |
| Nie et al. 2013 | Xylooligosaccharides increased levels of satiety hormones PYY and GLP-1 |
| Weickert et al. 2006 | Supplemental wheat fiber helped overweight women lose weight compared to control |
Toxicity and Obstruction Risks
While processed wood fibers may offer benefits, ingesting non-food materials still poses safety concerns. Even purified wood cellulose may irritate the digestive tract in sensitive people. Plus particles could potentially cause dangerous gastrointestinal obstructions if they accumulate and bulk together.
There are also risks of chemical toxicity with industrial wood products. Pressure-treated lumber contains toxic preservatives like chromium and arsenic that can leach out. Ingesting these chemicals poses threats like nausea, kidney or liver damage, and even cancer.
It’s important to note that research on purified wood derivatives doesn’t necessarily demonstrate the safety of eating wood itself. Any non-food material carries risks when ingested, especially in quantities larger than trace amounts.
Talk to your doctor before intentionally consuming significant amounts of wood fiber.
The Bottom Line
- Wood is primarily composed of cellulose, lignin, and other plant fibers that cannot be broken down by human digestive enzymes.
- Chewing on wood can damage teeth and splinters can puncture internal organs if swallowed.
- Although termites and some rodents have special gut bacteria to digest cellulose, humans lack these microbes.
- Small amounts of wood pulp or sawdust may pass through the GI tract undigested, while larger pieces are unlikely to be broken down.
- Accidentally ingesting wood is not normally harmful, but purposefully eating wood can cause obstructions and should be avoided.
In the end, while wood is not toxic, our human digestive system has simply not evolved to extract nutrients or energy from the tough woody fibers. Stick to eating food and leave the wood for home building and craft projects!
Conclusion
While humans can’t efficiently extract nutrients and energy from most types of wood due to limitations of our digestive system, we do have some capability to break down and absorb certain purified wood fibers.
Understanding what components of wood we may be able to partially digest and how they make their way through our gastrointestinal tract gives insight into this unusual question.
If you found this deep dive on whether humans can digest wood informative, be sure to check back as we explore related questions at the intersection of biology, nutrition and health.
