If feces are the waste products of digestion that animals expel through defecation, for some living beings they act as food or fertilizer, thus promoting the recirculation of nutrients on our planet. Humans have known this for a long time, which is why they use cow manure in fields as fertilizer.
Feces are also useful to science for studying and conserving nature, as they allow tracking species that are difficult to observe directly and obtaining diverse information about the animals that produced them, such as their DNA, what they eat, the level of some hormones such as stress and those related to reproduction.
Fossil feces (fossilized excrement is called coprolites ) allow researchers to investigate the past; for example, thanks to fossilized feces we discovered that our ancestors ate insects . But feces also provide clues for investigating the health of humans and other animals.
We defecate once or twice a day, expelling, on average, between 100 and 250 grams of feces. Therefore, poop is very familiar to all of us , but we often don't know much about it. Let's discover what it's made of, what makes it smell, and other interesting facts about it.
Composition of feces
From a young age, we are taught that we eliminate toxic or superfluous substances through feces. However, in addition to these waste products, other substances are also excreted in our stool.
The composition of our droppings includes:
- 75 % Water.
- Microorganisms, both alive and dead, at 7,5%. These derive from the intestinal microbiota, the set of microorganisms that inhabit our digestive tract and that have established a mutually beneficial relationship with us: it strengthens our immune system, helps digestion and produces useful substances, obtaining food thanks to us. It is estimated that there are about 30 trillion microorganisms (equivalent to about a third of our cells), mainly bacteria, in feces.
- indigestible organic matter derived from food for another 7,5%. The well-known dietary fibers fall into this category.
- Cholesterol and others fat around 3%.
- inorganic substances, such as calcium and zinc phosphate, around 3%.
- Proteins, such as digestive enzymes (the molecules that speed up the breakdown of some foods), about 0,03%.
- There are also dead cells from the intestinal tract, dead leukocytes (white blood cells), and bilirubin. The latter is a reddish-yellow molecule that is derived from the breakdown of hemoglobin and is responsible for the Brown color of our feces.
The composition and color of stool can vary depending on several factors, including diet , the speed of transit through the intestinal tract (which means greater absorption of nutrients and water the slower the transit), and the diversity of microorganisms living in symbiosis with us. In fact, a greater diversity in the gut microbiota is associated with better digestive health.
Dietary fiber is commonly associated with a fundamental condition for the body's well-being: bowel regularity. But that's just one of the benefits of a high-fiber diet. As has become clear in recent years, many other, perhaps still little-known, benefits have been observed, such as its protective role against cardiovascular disease, type 2 diabetes, and colon cancer.
Studying these factors is useful for detecting any intestinal pathology. However, it is not always possible to evaluate them in the laboratory. For this reason, stool grading scales based on appearance have been developed.
Under normal conditions, feces are made up of 75% water and 25% solid material including bacteria, fibers not digested, fat, inorganic material (Calcium y phosphates), mucus, desquamated intestinal cells and some proteins. A significant part of the fecal mass is not of food origin; in fact, stool is also formed during the fast.
What types of dietary fibers are there?
Dietary fiber is, by definition, that component of plant-based food that is not digestible by human endogenous enzymes. In fact, it reaches the large intestine intact, where it is, however, partially digested by the resident gut bacteria. From a chemical standpoint, it is a variety of molecules that are usually roughly divided into insoluble and soluble . Cellulose, lignin, and some hemicelluloses belong to the first group. Examples of soluble fiber include pectins, gums, and beta-glucans.
The different degree of solubility can be attributed to their structure. That of cellulose, formed by many repetitions of a single type of sugar and stabilized by hydrogen bonds in a highly ordered structure, makes access to water very difficult. On the contrary, the lower molecular weight and the presence of branches with free ends to form bonds favor its solubility.
Bristol scale
Features of the Bristol scale:
- stool color: brown due to chemical conversion of bilirubin to urobilin and stercobilin by bacteria and intestinal enzymes.
- Fecal odor: This is the result of bacterial breakdown of proteins in the intestines.
- stool consistency: Soft and cylindrical shape the size of the rectum.
- stool pH: normally neutral or slightly alkaline (6,8 – 7,5).
- amount of stool: 150 to 300 g of feces are produced daily.
The mean passage time of undigested food residues in the human intestine is 50 hours in men and 57 hours in women, with large intra-individual and inter-individual variations (minimum well below 20 hours and maximum above 100 hours).
Among the most widely used stool classifications in research and clinical settings is the Bristol Stool Shape Scale , which divides stool into seven types:
- separated into hard pieces, difficult to evacuate;
- in the form of salami, formed by lumps joined together and very evident;
- salami-shaped, but less hard, with cracks on the surface;
- sausage-shaped, smooth and soft;
- broken into soft pieces, easy to expel;
- in pasty pieces like flakes;
- liquid.
Types 3, 4 and 5 are the most common in healthy people, while types 1 and 2 indicate excessively slow intestinal transit and types 6 and 7 indicate excessively rapid intestinal transit, which does not allow sufficient absorption of the nutrients. nutrients present in food.
Why does poop smell?
Our bodies, through respiration and bodily fluids, release more than 2.000 volatile organic compounds (VOCs). These are gaseous chemicals that also contribute to air pollution. Our feces contain more than 400 of them. Essentially, the odor we associate with feces is partly due to these compounds, derived from the bacterial metabolism that takes place in our intestines.
In particular to:
- Skatole (3-methylindole);
- Mercaptans. Some of these substances are known to be produced by animals such as the skunks and the skunks;
- indole (or benzopyrrole). Interestingly, this ingredient is also used in perfumes! In fact, it doesn't smell bad: it can also be found in the oils of the jasmine and orange plants;
- Hydrogen sulfide, a very toxic compound (but present in very small amounts).
Do you know how strong your poop smells after holiday dinners? Meat, dairy products, and alcohol make bowel movements smellier than those of people with primarily plant-based diets, as they contain sulfates or, in large quantities, are more difficult to digest. Alcohol can also interfere with bowel movements. The use of medications, supplements, certain sugars, and the presence of certain illnesses can also contribute to foul-smelling stools.
But why do we perceive feces as smelly? A chemical substance doesn't smell in and of itself: it's all a matter of the anatomical structures of the olfactory system and brain interpretation. Our perception of the pleasantness of smells varies from culture to culture, from person to person, and from age to age. And, of course, there are differences from species to species: we can think of dogs, who seem much less averse than we are to smelling excrement. It's possible that, as with other animals, the disgust that feces provokes protects us from possible parasites and pathogens contained within them.
What about the feces of other animals?
As with other animal species, the main component of feces is generally water. They often also contain highly visible elements that reflect what the animal has been eating, making a visit to the National Poop Museum (located in Sandown, Isle of Wight, Great Britain) very interesting.
The feces of carnivorous mammals contain remains of the animals they feed on, such as feathers, claws, and exoskeletons. The same is true for other predators, such as crows, in whose droppings small bones or beetle wings can be found. In general, however, bird guano is not easily distinguishable from one species to another: it has a solid, brownish component of indigestible food (the feces themselves) and another liquid, white component, since it is expelled along with urine, rich in mucus and urates, crystals of a white substance (uric acid).