Which is healthier, smelly stool or no smell? If you have this smell, beware of cancer

Expert of this article: Cheng KT, Master of General Medicine, Peking University Health Science Center

This article was reviewed by Meng Qingcheng, chief physician of general surgery at Beijing Aerospace Center Hospital (Peking University School of Aerospace Clinical Medicine), associate professor at Peking University, third-batch health science popularization expert in Beijing, doctor of medicine

High-energy warning ahead: This is an interesting popular science article.

In life, you who have a sensitive sense of smell may have noticed that some people’s feces are “stinky” while some people’s feces have very little odor.

Why does feces smell? What disease signals are indicated by different smells of feces? Can we tell who is healthier by looking at the smelly and non-smelly feces?

Are you ready? Read on.

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How does poop smell occur?

When we ingest food, it slides down the esophagus, stomach, and small intestine, which are responsible for digestion and absorption, into the large intestine, which means that the chyme has been processed by the gastrointestinal tract. In other words, after the food is extracted and the dregs are removed by the human digestive tract, the food residues finally discharged through the anus are the real body of feces.

Normal feces are composed of 3/4 water and 1/4 solid matter. About 30% of these solid matter are intestinal microorganisms from the dead feces field, 30% are "fat intestine stew" mixed with undigested food, digestive juices and desquamated epithelial cells, 10%-20% are inorganic matter, and 2%-3% are protein.

The smell of human feces is closely related to the intestinal microbiome. Microbiologists estimate that under normal circumstances, there are at least 500 different microorganisms in the human gastrointestinal tract, with an order of magnitude of up to 100 trillion and a weight of about 1 kilogram. Most of them are bacteria, but there are also viruses, fungi and protozoa, which are mainly distributed in the ileum and large intestine.

The mission of these powerful intestinal microorganisms is to assist food digestion and prevent the invasion of pathogenic microorganisms. Food fermentation produces carbon dioxide, oxygen, methane, hydrogen sulfide, mercaptan and other gases, which merge into a "heart-stirring" smelly intestinal gas.

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The intestinal microbiota can also produce metabolites such as skatole (one of the ingredients that makes stinky tofu smell so good) and indole (low concentrations have a floral scent, while high concentrations are notorious), which can give your stool a "unique flavor".

Why does poop have different smells?

Feces itself often has a bad smell, but the severity varies, and the human sense of smell may not be able to detect it clearly, so some people describe it as rotten eggs, fish, or garlic.

In life, chefs can cook dishes with unique flavors by adding different types and proportions of seasonings. Similarly, when we consume different types of food every day, the composition ratios of nutrients such as protein, carbohydrates, and lipids are different, which makes the proportions of various metabolites in the excrement different, resulting in individual differences in the smell of feces. This is also the reason why "meat eaters have strong taste and vegetarians have light taste".

In addition, due to the lack of certain digestive proteases in the human body, excessive intake of certain foods, etc., the gastrointestinal processing may not be able to completely wash away the smell of the food itself, so the smell may still remain in the food residue. For example, if you eat too much durian or garlic, your body may excrete stools with the smell of durian or garlic.

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In addition to dietary structure, the odor of stool may also be related to factors such as digestive system or systemic diseases, bowel habits (stool frequency), intestinal flora, etc. For example, constipated people with less frequent bowel movements may have intestinal flora imbalance. Since stool and intestinal bacteria have sufficient opportunities for lingering contact, just like wine, the longer the fermentation time, the more fragrant it becomes, and the stool may also have a stronger odor.

What diseases do different stool odors indicate?

Normal feces discharged by the human body have a slight odor, but it is usually not strong. Even if the odor is strong sometimes, it will generally disappear in a short time.

The abnormal odor of stool can be further divided into fishy, ​​sour or foul. These abnormal odors may be clues to human gastrointestinal diseases.

For example

Fishy-smelling stools may indicate amebic enteritis

A sour-smelling stool may be caused by a disorder involving the breakdown of fatty acids or abnormal fermentation of sugars.

Foul-smelling stools may indicate chronic enteritis, severe dysentery, gastrointestinal bleeding, chronic pancreatitis or pancreatic cancer, or colorectal cancer.

The smell of stool may be a "barometer" of digestive tract health. This is why stool odor is one of the important physical parameters in routine stool examinations in medicine, and it may provide important diagnostic clues especially in the early stages of the disease.

However, it should be noted that the presence or absence of odor in stool alone cannot directly determine whether it is related to intestinal health. Even professionals still need to comprehensively consider the patient's clinical manifestations, parameters such as stool color or characteristics, stool culture, and imaging examination results such as colonoscopy to make a correct diagnosis of the disease.

How can I make my poop less smelly?

In addition to timely treatment of gastrointestinal diseases and maintaining intestinal health, good habits in diet, exercise and bowel movements are also beneficial for deodorizing stools.

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Drink enough water, eat and exercise in a balanced way, and have a balanced diet

According to the recommendations of the 2022 Chinese Dietary Guidelines, the daily water intake for normal men and women is 1700 ml and 1500 ml respectively. Exercise regularly and perform moderate-intensity activities (150 minutes cumulatively) at least 5 days a week.

Control sugar and limit alcohol, eat less oil and salt, avoid overeating, and eat more dietary fiber, including cereals and potatoes (200-300 grams/day), fresh vegetables (300 grams/day) and fruits (200-350 grams/day). It is best to eat 300-500 grams of fish, eggs and 300-500 grams of livestock and poultry meat per week.

Develop good bowel habits

The standing reflex in the morning helps promote large intestine movement and the urge to defecate, so the large intestine is most active after waking up in the morning (men usually defecate between 7 and 8 in the morning, and women about an hour later than men). On the other hand, eating can easily induce the defecation reflex, which is conducive to successful defecation. Therefore, it is recommended to try to defecate in the morning or within 2 hours after a meal.

In addition, you should concentrate when defecating and reduce interference from external factors such as playing with mobile phones and reading. It is recommended that each bowel movement should not exceed 10 minutes.

Healthy living, eating and exercise habits can help maintain stool moisture, stimulate intestinal peristalsis and control stool characteristics, which in turn helps to ensure bowel movement frequency, prevent constipation and improve intestinal flora imbalance, which may reduce stool odor.

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