What is in feces?
Feces, or stool, is the body’s waste product remaining after the digestive system has absorbed most of the nutrients from food and drink. A healthy human's feces is typically composed of about 75% water and 25% solid matter. This solid content is not the nutrient-rich food you consumed, but rather a complex mixture of other substances.
Key components of the solid matter include:
- Dead and living bacteria: These microorganisms make up a significant portion of the solid waste, sometimes 25–54% of the dry weight.
- Indigestible food matter: This primarily consists of dietary fiber, such as cellulose from plant-based foods, that the human body cannot break down.
- Intestinal secretions and shed cells: The body continuously replaces the cells lining the digestive tract, which are then passed in the stool.
- Fats and Cholesterol: Waste products from fat digestion and cellular processes are also present.
- Inorganic substances: These include salts like calcium and iron phosphates, which are not absorbed by the body.
Not all feces are created equal: A comparison
The presence of some nutrients and organic matter in feces leads to a common misconception. It's crucial to distinguish between the potential uses of feces in nature and the significant health risks associated with human consumption. Below is a comparison illustrating the stark difference between human and animal interactions with feces.
| Aspect | Animal Coprophagy (e.g., rabbits, some rodents) | Human Ingestion |
|---|---|---|
| Purpose | Re-digestion of special fecal pellets (cecotropes) to absorb missed nutrients or to acquire beneficial gut microbes. | None. Extremely dangerous and unsanitary practice. |
| Health Impact | Can provide essential vitamins (B and K) and a healthy gut microbiome, which is vital for proper digestion. | High risk of contracting life-threatening diseases, parasites, and infections. |
| Feces Type | Some animals produce specific pellets rich in microbes and nutrients intended for re-ingestion, distinct from their regular waste. | All human waste contains high concentrations of potentially harmful pathogens, regardless of appearance. |
| Safety | An evolved, natural, and necessary behavior for certain species to survive. | Considered a minimally toxic exposure in small accidental amounts, but intentionally eating it is never safe. |
| Controlled Use | Necessary for newborns of species like koalas and elephants to acquire a gut microbiome for digesting vegetation. | Only performed in a sterile, medical setting via fecal microbiota transplants (FMT) for treating severe infections like C. difficile. |
The dangers of consuming feces for humans
For humans, feces is a biological hazard. It is not a nutritional source but a vector for disease transmission. The gut contains a vast and diverse community of microbes, and what is safely contained within the intestines can cause serious illness if ingested orally.
High pathogen and parasite risk
Human and animal feces are filled with pathogens that can cause severe infections when consumed. These include:
- Bacteria: Salmonella, E. coli, Shigella, and Campylobacter are common in fecal matter and can cause food poisoning-like symptoms such as severe diarrhea, vomiting, and abdominal pain.
- Viruses: Hepatitis A and Norovirus can be transmitted through fecal contamination, leading to liver inflammation or severe gastrointestinal distress.
- Parasites: Microscopic organisms like Giardia and Cryptosporidium can cause parasitic infections with symptoms including diarrhea and dehydration.
Fecal transplants vs. casual ingestion
It is important to differentiate between intentional, medically-supervised procedures and the dangerous practice of casual ingestion. Fecal microbiota transplantation (FMT) is a highly regulated medical procedure in which stool from a rigorously screened, healthy donor is transferred to a patient to restore a healthy gut microbiome. This is a complex medical treatment for specific conditions, not a recreational or dietary activity.
Feces as a nutrient source (for plants)
While not edible for humans, feces do contain valuable plant nutrients and have been used as a fertilizer for centuries. Human waste contains essential macro and micronutrients like nitrogen, phosphorus, and potassium, which are crucial for plant growth. However, this requires careful and extensive processing, such as hot composting, to kill pathogens before it can be safely applied to non-edible crops. The use of human waste as fertilizer highlights its ecological role as a source of nutrients for the soil, not as a food source for humans.
Conclusion: Waste is not a source of nutrition
In summary, the notion of consuming feces for nutrition is a dangerous and unscientific idea for humans. Although our waste contains some organic material and traces of nutrients, this is not in a bioavailable form and is overshadowed by the high concentration of harmful pathogens and bacteria. While certain animal species have evolved specific digestive strategies that involve consuming feces (coprophagy), humans have not. The human body is highly efficient at absorbing nutrients, and what is excreted is simply waste. The only safe and beneficial way for humans to utilize fecal matter is through strictly controlled medical procedures or by properly sanitizing it for use as fertilizer. For more information on the gut microbiome's role in health, visit the National Institutes of Health.
