Feces, also known as poop, are the solid waste material remaining after the body absorbs nutrients from food. This is the body’s primary method for expelling indigestible matter and other unneeded byproducts. This process is a fundamental aspect of digestion, ensuring the removal of substances that could otherwise accumulate.
The Body’s Waste Production
Food transforms into waste as it moves from the mouth, through the esophagus, to the stomach. Here, digestive enzymes and acids break food down into a semi-liquid mixture called chyme. This chyme then moves into the small intestine, where the majority of nutrient absorption occurs, including vitamins and minerals.
As this digested material progresses into the large intestine, water absorption becomes its primary function. The large intestine reclaims significant amounts of water, essential for compacting the waste. This process gradually forms the solid waste known as feces by removing excess liquid from the indigestible residue.
The colon’s muscular contractions, called peristalsis, propel this compacting waste towards the rectum. This movement allows for efficient water extraction and the final shaping of the stool before elimination through the anus.
What Poop Contains
Human feces are primarily composed of about 75% water, with the remaining 25% consisting of solid matter. This solid portion is a complex mixture, not just undigested food. A substantial part of the dry solid matter comprises dead bacteria, originating from the gut microbiome, which play a significant role in digestion.
Beyond bacteria, feces also contain indigestible food matter, such as cellulose and other fibers. Shed cells from the intestinal lining, mucus, and bile also contribute to its composition. Bile pigments, particularly bilirubin derivatives, are responsible for the characteristic brown color of feces. Other components include small amounts of protein, fat, and inorganic substances.
After It Leaves the Body
Once feces leave the body, their disposal depends on the system in place. In urban and suburban areas, waste enters a vast network of sewer pipes that transport wastewater to a centralized sewage treatment plant.
At these plants, wastewater undergoes multiple stages of treatment to remove contaminants. Initial steps screen out large objects, followed by primary treatment where solids settle into sludge. Secondary treatment uses biological processes, often involving microbes and aeration, to break down remaining organic matter.
The treated water is then disinfected before being returned to rivers or the sea. The sludge is further processed, sometimes used as fertilizer or for energy generation.
In rural areas without municipal sewer systems, septic systems are commonly used. A septic tank collects household wastewater, allowing solids to settle as sludge and lighter materials to float as scum. Naturally occurring bacteria within the tank break down some waste.
The liquid then flows into a drain field, where soil acts as a natural filter, removing contaminants before the water re-enters the groundwater. In natural settings, feces decompose through bacteria, fungi, and insects, returning nutrients to the soil.
Understanding Poop’s Appearance
The appearance of feces, including color and consistency, offers clues about digestive health. Normally, human feces are light to dark brown, a color derived from bile pigments like stercobilin and urobilin. Color variations can be attributed to diet, such as green leafy vegetables or certain food dyes leading to green stools, or beets causing red hues.
However, changes like black or tarry stools might indicate bleeding in the upper gastrointestinal tract. Pale or white stools could suggest issues with bile production, while yellow, greasy stools may point to excess fat due to absorption problems.
Consistency is another important indicator, often assessed using the Bristol Stool Chart. This chart categorizes stool into seven types, ranging from hard, separate lumps (Type 1, indicating constipation) to entirely liquid (Type 7, indicating diarrhea). Types 3 and 4, described as sausage-shaped with cracks or smooth and soft, are generally considered healthy and easy to pass. Deviations from these normal types can signal digestive disturbances. While temporary changes are common, persistent alterations in color, consistency, or frequency may warrant attention.