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What is the composition of human feces?

What is the composition of human feces?


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Are there any studies or general information on the composition of human feces?

I'd specifically like to know the percentage of carbohydrates and amino acids relative to the amount that was ingested in diets of various types and amounts.

Any additional facts are also welcome.


This is a bit hard because the usual composition statements are a combination of different types of molecules.

Most of faeces are, by dry weight, bacteria (30%), undigested food and fiber (30%), fat (10%-20%), inorganic matter( 10-20%), other protein(2-3%). (reference)

As you can see the bacterial portion contains proteins (amino acids) and other types of molecules. the inorganic matter includes bilins which are part of the used up hemoglobin from red blood cells which have been retired.

There's also a lot of variation from one sample to the next - 10% seems pretty common here as you can imagine). What makes faeces so dangerous is the bacterial portion, which can pose quite a health risk.


The exact chemical composition of human flatulence varies from one person to another, based on his or her biochemistry, the bacteria inhabiting the colon, and the foods that were eaten. If the gas results from ingesting air, the chemical composition will approximate that of air. If the fart arises from digestion or bacterial production, the chemistry may be more exotic. Farts consist primarily of nitrogen, the principal gas in air, along with a significant amount of carbon dioxide. A typical breakdown of the chemical composition of farts is:

  • Nitrogen: 20-90%
  • Hydrogen: 0-50% (flammable)
  • Carbon dioxide: 10-30%
  • Oxygen: 0-10%
  • Methane: 0-10% (flammable)

A National Human Feces Bank

You’ve heard of blood banks, but did you know that there is now a national non-profit banking system for human feces? “Why?”, you might ask. Well, it turns out that fecal transplants (either by nasoduodenal tube or by bowel lavage) are quite effective at treating recurrent infections of a particularly dangerous type of gastrointestinal infection.

The gastrointestinal infection in question is caused by a bacterium called Clostridium difficile. Under normal conditions, C. difficile is just one of thousands of types of normal bacteria that inhabit the gut. When most of the gut bacteria are wiped out, for example by the use of antibiotics, C. difficile may take over, producing a toxin that causes recurrent diarrhea. Infections by C. difficile kill more than 12,000 Americans a year, according to the CDC. C. difficile infections are not very responsive to antibiotics, making them difficult to treat.

Last year, research showed that fecal transplants were much more effective at treating infections of C. difficile than the best antibiotic treatment available. Apparently, by reintroducing a wide variety of normal bacteria back into the gut, fecal transplants prevent C. difficile from gaining a sufficient advantage to make the patient sick.

Until now, though, there was not been a source of standardized preparations of human feces. Patients had to rely on fecal donations from relative or friends, which some patients consider a little embarrassing. In addition, health professionals were on their own in terms of preparing and administering donated feces.

A national human feces bank seems like an idea that could work, despite the “yuck” factor. We’ll see how (or whether) it gains widespread support from patients and health professionals.


The secret to the speed

What else did we learn? Bigger animals have longer feces. And bigger animals also defecate at higher speed. For instance, an elephant defecates at a speed of six centimeters per second, nearly six times as fast as a dog. The speed of defecation for humans is in between: two centimeters per second.

Together, this meant that defecation duration is constant across many animal species &ndash around 12 seconds (plus or minus 7 seconds) &ndash even though the volume varies greatly. Assuming a bell curve distribution, 66 percent of animals take between 5 and 19 seconds to defecate. It&rsquos a surprisingly small range, given that elephant feces have a volume of 20 liters, nearly a thousand times more than a dog&rsquos, at 10 milliliters. How can big animals defecate at such high speed?

The answer, we found, was in the properties of an ultra-thin layer of mucus lining the walls of the large intestine. The mucus layer is as thin as human hair, so thin that we could measure it only by weighing feces as the mucus evaporated. Despite being thin, the mucus is very slippery, more than 100 times less viscous than feces.

During defecation, feces moves like a solid plug. Therefore, in ideal conditions, the combined length and diameter of feces is simply determined by the shape of one&rsquos rectum and large intestine. One of the big findings of our study was that feces extend halfway up the length of the colon from the rectum.


Laboratory testing of feces

Feces will sometimes be required for microbiological testing, looking for an intestinal pathogen or other parasite or disease.

Biochemical tests done on feces include faecal elastase and faecal fat measurements, as well as tests for faecal occult blood.

It is recommended that the clinician correlate the symptoms and submit specimens according to laboratory guidelines to obtain results that are clinically significant. Formed stools often do not give satisfactory results and suggest little of actual pathologic conditions.

Three main types of microbiological tests are commonly done on feces:

  • Antibody-antigen type tests, that look for a specific virus (e.g. rotavirus).
  • Microscopic examination for intestinal parasites and their ova (eggs).
  • Routine culture.

Routine culture involves streaking the sample onto agar plates containing special additives, such as MacConkey agar, that will inhibit the growth of Gram-positive organisms and will selectively allow enteric pathogens to grow, and incubating them for a period, and observing the bacterial colonies that have grown.


What is the composition of feces?

Contains undigested food residues, mucus, millions of bacteria and just enough water to allow their smooth passage.

This answer is only partially corrrect and does not address the question properly.

While feces do contain millions of bacteria, feces do not always contain enough water to facilitate smooth passage.

In addition, fecal matter is composed of a plethora of toxic chemicals that are the waste products of the bacterial action that goes with food decomposition.

Those toxins are referred to frequently in medical literature but never identified.

At the same time, those same chemicals are root causes of virtually every degenerative health condition and many mental conditions as well.

This is well known to medical scientists but they aren't doing the work to figure out exactly what the chemicals are. This is important because when a bowel blockage occurs, the toxic chemicals pass through the colon walls into the blood stream causing physiolical havoc.


Materials and methods

Population recruitment, sample collection, and DNA purification

Healthy adults 18 to 40 years old were recruited at two academic centers [10]. Fifteen and 18 body habitats were collected from enrolled males and females, respectively. The sites sampled included anterior nares, oropharynx (two specimens), oral cavity (seven specimens), skin (four specimens), stool, and vagina (three specimens per female) [10]. The Manual of Procedures and the Core Microbiome Sampling Protocol are available at the Data Analysis and Coordination Center for the HMP [99], as well as dbGaP [100]. Genomic DNA was isolated from the collected samples using the MO Bio PowerSoil DNA Isolation Kit (MO BIO laboratories, Inc., Carlsbad, California, USA) [10].

Sequencing and binning of 16S rRNA genes and read processing

Detailed protocols used for 16S rRNA bacterial gene amplification and sequencing, using the 454 FLX Titanium platform and kits (Roche Diagnostic, Corp., Indianapolis, Indiana, USA), are available on the HMP Data Analysis and Coordination Center website [99], and are also described elsewhere [10]. In brief, sequences were processed using a data curation pipeline implemented in mothur [10, 101] starting with quality trimmed for homopolymer runs and a minimum 50 bp window average of 35. Any sequences not aligning against the appropriate subset of the SILVA database [102] were removed, as were chimeric sequences. Resulting sequences were processed using a data curation pipeline implemented in mothur [10, 101]. Remaining sequences were classified with the MSU RDP classifier v2.2 [29] using the taxonomy maintained at the RDP (RDP 10 database, version 6). Definition of a sequence's taxonomy was determined using a pseudobootstrap threshold of 80% [10].

16S rRNA gene dataset post-processing and quality control

A table of read counts from the 16S rRNA bacterial gene pipeline was created by summing clade counts from the three regions and was further processed for removing low-coverage samples. Firstly, those taxa not supported in the whole dataset by at least two sequences in at least two samples were removed. Then, the quality control procedure compared, for each sample, the read count of the most abundant taxon t and the highest abundance value that the same taxon t achieved in the entire dataset. If the former term of the comparison is <1% of the latter, the sample was discarded. Second, third, and fourth time-point samples from the same subjects were discarded. The resulting dataset of read counts containing 2,105 samples is reported in Additional file 12, which represents 210 ± 7 samples per body site. Further analysis of the dataset was performed using the per sample normalization to relative abundances. In the text, mean values are presented with standard deviation. The number of subjects with samples in the digestive tract retained for the 16S rRNA-based analysis was 209 post-quality control, from which 147 had sample data for all 10 body sites post-quality control. Unless otherwise noted, only first visit samples were used in all analyses.

Biomarker discovery and visualization

The characterization of functional and organismal features differentiating the microbial communities specific to different body sites in the digestive tract was performed using our method for biomarker discovery and explanation called LEfSe [30]. LEfSe, publicly available [103], couples a standard test for statistical significance with a quantitative test for biological consistency, finally ranking the results by effect size. Briefly, it first uses the non-parametric factorial Kruskal-Wallis test to detect features (taxonomic clades or metabolic pathways) with abundances that differ below a significance threshold among groups of samples. Biological consistency is subsequently tested using the unpaired Wilcoxon rank-sum test among all pairs of sample groups in our case this occurred between single body habitats. Finally, linear discriminant analysis (LDA) with bootstrapping is then used to rank differentially abundant features based on their effect sizes. A significance alpha of 0.05 and an effect size threshold of 2 were used for all biomarkers discussed in this study. Organismal and functional biomarkers are graphically represented here on hierarchical trees reflecting the RDP taxonomy [29] for 16S rRNA gene data and the KEGG BRITE hierarchy [49] on KEGG modules for metagenomic functional data.

Clustering and statistical significance of four groups of body site habitats

For assessing bacterial community structure similarities between different samples and body sites, we compared the relative abundances of every pair of samples in our dataset using the Bray-Curtis measure of beta diversity [31]. The comparisons have been summarized in terms of within- and between-group averages as reported in Table 1 moreover, statistical significance has been tested for within versus between group distances, providing strong support (all P-values <10 -20 ) for the clustering of all four groups in distinct community structures. A multidimensional scaling analysis was then performed on the Bray-Curtis diversity matrix and the four groups were denoted with different colors for highlighting the clustering structure (Additional file 4).

Whole genome shotgun sequencing, read processing, and community metabolic profiling

Whole genome shotgun sequencing employed the Illumina GAIIx platform (Illumina, Inc.) as previously described [10]. The number of samples and nucleotide content from 98 subjects is summarized in Additional file 12. The abundances and presence (or absence) of pathways in these metagenomic data were inferred using the HUMAnN pipeline (HMP Unified Metabolic Analysis Network) [48]. Briefly, the metabolic and biomolecular potential of each sample was profiled starting from the 100 bp Illumina sequences after quality and length filtering. Reads were mapped to KEGG v54 orthologous gene families (KEGG KOs [49]) using MBLASTX (MulticoreWare, St. Louis, MO, USA), an accelerated translated BLAST implementation, using default parameters and a maximum E-value of 1. Hits were mapped to abundances of each KO using up to the 20 most significant hits, weighted by the quality of each hit (inverse blastx P-value) and normalized by the length of the hit gene. Pathway information was then recovered by assigning KO gene families to KEGG modules (representing small pathways of approximately 5 to 20 genes) using a combination of MinPath [104], filtering of pathways not consistent with the BLAST-derived taxonomic composition of the community, and gap filling of likely missing enzymes. The resulting KO and KEGG module relative abundances were used in the presented analysis. Further details of the HUMAnN methodology, its software implementation, and an extensive validation of each computational step appear in [48].

Data accessibility

The datasets used in these analyses were deposited by the NIH Common Fund Human Microbiome Consortium at the Data Analysis and Coordination Center (DACC) for the Human Microbiome Project. Specifically, the downloadable packaged datasets are the 16S rRNA gene dataset [105], phylotype-classification of the 16S rRNA gene dataset [106, 107], Human Microbiome Illumina whole genome shotgun reads [108], and the metabolic reconstruction tables [109]. The phylotype classification processed for normalization and quality control is available in Additional file 7.


Can COVID-19 spread through fecal matter?

Early studies show evidence of COVID-19 genetic material in fecal matter, but more work is needed to determine if the virus can be spread through stool, according to a new review paper from a Rice University epidemiologist.

"Potential Fecal Transmission of SARS-CoV-2: Current Evidence and Implications for Public Health" will appear in an upcoming edition of the International Journal of Infectious Diseases and is available online. The paper reviewed an ever-changing body of literature on detection of the novel coronavirus in fecal matter of COVID-19 patients.

"Most of the studies that have been done so far are picking up viral RNA in the feces rather than infectious virus," said E. Susan Amirian, an epidemiologist with Rice's Texas Policy Lab and the study's lead author. "However, a few studies have showed that infectious virus may be present in stool samples."

Amirian said the mere presence of genetic material is less worrisome than if infectious amounts of viable virus are found in stool in future studies, as that would imply it is possible for it to be transmitted to others through feces. She said if future research continues finding viable virus in stool, this could have important implications, especially for those working in the restaurant industry, nursing homes, day cares, etc.

"Ultimately, more research is needed to determine whether exposure to stool is spreading this virus and making the pandemic worse," Amirian said. "But given this possibility, it behooves us to be more careful, especially in settings where people have an increased risk of morbidity and death due to COVID-19."

Amirian said there's no downside to exercising an abundance of caution in following good personal hygiene practices until we know more.

"There are plenty of other diseases out there that are transmitted through fecal contamination, including hepatitis A and norovirus," she said. "Following a high level of precaution will help just in case COVID-19 can be spread this way."


Ancient human faeces reveal gut microbes of the past

Matthew R. Olm is in the Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California 94305, USA.

You can also search for this author in PubMed Google Scholar

Justin L. Sonnenburg is in the Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California 94305, USA and at the Center for Human Microbiome Studies, Stanford University School of Medicine.

You can also search for this author in PubMed Google Scholar

The microbial cells that inhabit the human gut, collectively called the gut microbiota or microbiome, have key influences on our metabolic and immune-system biology 1 , 2 . Many microorganisms are passed down over the generations 3 , 4 . However, the gut microbiota (tracked by analysing the microbial DNA in faeces) can be radically reshaped within days to months of certain events, such as immigration into a different country 5 or antibiotic treatment 6 . Defining which microbes were once part of our evolutionary history and have since been lost might provide a key to understanding the relationship between microbes and human health. Writing in Nature, Wibowo et al. 7 address this issue by turning to a microbial ‘time machine’: palaeofaeces. By using DNA sequencing to study the microbiomes of human stool samples that are 1,000–2,000 years old, this study provides valuable insights into gut microbes from a time before industrialization.

Read the paper: Reconstruction of ancient microbial genomes from the human gut

The human microbiome is a malleable component of our biology that adapts to specific circumstances, for example displaying seasonal variation corresponding to food availability 8 . Although this malleability offers a potential avenue for the treatment of human diseases linked to microbiota, it is also a vulnerability. Many aspects of industrialized life, such as antibiotic use and a fibre-deficient Western diet 9 , 10 , have a negative effect on gut microbes.

Which core microbes and microbial functions from the pre-industrial microbiota were lost as societies became industrialized? Certain broad bacterial groups (referred to as ‘volatile and/or associated negatively with industrialized societies of humans’ (VANISH) taxa) are highly prevalent in present-day Indigenous populations living traditional lifestyles, but are rare or absent in industrialized populations 10 . There are also numerous bacterial taxa (referred to as ‘bloom or selected in societies of urbanization/modernization’ (BloSSUM) taxa) that have the opposite pattern 10 . Whether present-day non-industrialized populations have microbiotas that are similar to those of humans who lived thousands of years ago has remained an open question, until now.

Wibowo et al. report DNA-sequencing analysis of 15 samples of palaeofaeces collected from the southwestern United States and Mexico. Seven of these samples were excluded for further study because of poor-quality DNA or evidence of soil contamination, or because the sample was found to come from a canine host. The age of the eight remaining samples was determined using carbon dating, and analysis of DNA damage revealed hallmarks that confirmed the antiquity of the material (ancient DNA has specific characteristics of degradation). The human origin of these samples was validated by microscopic analysis of dietary remains present in the palaeofaeces and by evidence of human mitochondrial DNA.

Identifying gut microbes that affect human health

The high quality of the data generated enabled the authors to detect known microbial species and to discover previously unknown microbes through the reconstruction of microbial genomes. A total of 181 of the 498 reconstructed microbial genomes were classified as gut derived and had extensive DNA damage, consistent with an ancient origin, and 39% of the ancient genomes offered evidence of being newly discovered species.

Wibowo and colleagues compared their data from the ancient gut samples with data from a collection of previously sequenced stool samples from present-day populations with industrialized and non-industrialized lifestyles. The species Treponema succinifaciens, a microbe in the Spirochaetaceae family shown to be lost from industrial populations 8 , was present in palaeofaeces, as were other VANISH taxa that were absent in industrialized samples and prevalent in non-industrialized samples. BloSSUM taxa, including the species Akkermansia muciniphila (which degrades human mucus), were more abundant in the industrialized samples than in the non-industrialized samples and the palaeofaeces. Together, these results support the idea that features of non-industrialized microbiomes are similar to the microbiomes of our human ancestors, and that industrialized populations have diverged from this microbial signature (Fig. 1).

Figure 1 | A comparison of ancient and modern human gut microbes. Wibowo et al. 7 analysed the DNA of gut microbes found in 1,000–2,000-year-old human palaeofaeces, and compared this with the DNA of gut microbes in faecal samples from present-day individuals from industrialized and non-industrialized societies. The authors used a statistical method called principal component analysis to compare the patterns of bacterial species present in the samples from each individual. This approach distributes data points corresponding to each individual’s sample along two axes, termed PC1 and PC2. Samples that are more similar to each other are grouped more closely together on the graph. This analysis reveals that the samples of palaeofaeces are distributed among those from individuals living in non-industrialized societies, indicating a similarity of gut-microbe profiles between ancient humans and modern humans living traditional lifestyles — both of which are distinct from the microbial profile of people in industrialized societies. (Figure based on Fig. 1b of ref. 7.)

The authors moved beyond focusing on species identity: they compared the genes, and the predicted functions of the proteins encoded by those genes, for the microbes in palaeofaeces with those found in present-day samples. Both the industrialized and the non-industrialized present-day samples had a greater prevalence of antibiotic-resistance genes than did the palaeofaeces, a finding consistent with the ancient microbes being from before the era of antibiotic use. Palaeofaeces had a high prevalence of genes encoding proteins that can degrade the molecule chitin, a component of insect exoskeletons. This finding is consistent with human consumption of insects, known to be a component of ancestral diets. Insect ingestion was confirmed by the authors’ microscopy analysis of material in the palaeofaeces. The authors report many genes that were particularly prevalent in industrialized samples, including those involved in the degradation of mucus in the human gut.

Wibowo and colleagues’ study is a remarkable technical achievement. They were able to recover high-quality DNA from microbial organisms that lived thousands of years ago, probably because of the good preservation possible in the dry desert environment in which the samples were located. Multiple independent lines of evidence authenticated the sample age and the human origin of the faeces. Having these ancient DNA sequences available in the public domain will undoubtedly benefit scientists for years to come.

Bacterial species singled out from a diverse crowd

However, DNA-sequence-based analyses do have limitations when the results are not paired with validation by other types of laboratory experiment. Using computational tools to predict information about proteins encoded by DNA is an imperfect method under ideal conditions, and is particularly tricky when analysing gene functions for previously unknown organisms, such as those discovered in this study. Moreover, microbiomes are highly variable between individuals and between populations. Analyses of more palaeofaeces from a wider range of timescales and locations will be needed to better understand general and population-specific features of ancient human gut microbiomes.

The authors found notable differences in the composition and function of microbes in palaeofaeces compared with those of microbes in present-day faeces. The higher prevalence of mucus-degrading species and genes in industrialized microbiomes than in ancient and non-industrialized ones is probably driven by Western diets, which often lack sufficient dietary fibre to support once-numerous fibre-degrading microbial species 11 , 12 . Given the links between the microbiome and the immune system, these differences might be connected to the rising rates of autoimmune, inflammatory and metabolic disorders in industrialized populations 9 , 10 .

Wibowo and colleagues’ work indicates that there are now two viable alternatives to time travel for understanding the composition of ancient microbiomes. Palaeofaeces enable the direct investigation of ancient microbiomes, but the sample age limits the further measurements and experiments that can be performed. Importantly, this study validates that present-day Indigenous populations living traditional lifestyles have similar microbiome compositions to those of ancient humans. It is essential to acknowledge that most of these present-day populations are marginalized, lead a vulnerable existence, and require exceptional protections to ensure they are not exploited. With ethically conducted research, these modern populations might open a window on our microbial past.

Nature 594, 182-183 (2021)


The Value of Human Feces

Human excreta are comprised of two basic components, urine and faeces. When urine and faeces are kept apart, they have different properties, are produced in different quantities, and require different care in processing. Published figures indicate that more than 1 kg of urine is produced daily, while less than 150 g of faeces, including moisture, is produced daily. 11 These figures, of course, vary by type of diet, location, age, activity and health status.

Urine contains nearly 80% of the total nitrogen found in excreta (Table 1). Urine also contains two-thirds of the excreted phosphorous and potassium. The majority of the carbon excreted, up to 70%, is found in faeces. The quantities shown above may suggest that excreta contain few nutrients. Each person urinates annually about 4 kg of nitrogen, 0.4 kg of phosphorous, and nearly 1 kg of potassium total excretion is 4.5 kg of nitrogen, more than a half kg of phosphorous, and 1.2 kg of potassium. In an urban setting of 10 million people, this equates to 45 million kg of nitrogen, nearly 6 million kg of phosphorous, and more than 12 million kg of potassium. It also represents 10 million litres of nutrient rich and mostly sterile water that is excreted. The water that is not flushed by 10 million people equates to 0.15 km3 of water saved by using ecological sanitation, fresh water that could be used for other purposes, such as food production, without risk of infection. Other elements, such as calcium and magnesium, are excreted in nearly equal amounts in urine and faeces. There are many other nutrients found in human excreta, but they are not shown above. Although using only urine is valuable, both urine and faeces should be recovered and recycled to avoid long term depletion of soils.

Elements (g/ppd) Urine Faeces Urine + faeces
Nitrogen 11.0 1.5 12.5
Phosphorous 1.0 0.5 1.5
Potassium 2.5 1.0 3.5
Organic carbon 6.6 21.4 30
Wet weight 1,200 70-140 1,200-1,400
Dry weight 60 35 95
Table 1: Select components found daily in human excreta per person 12

Globally, 2 billion hectares have been degraded since World War II, 23% of globally used land. 13 If only agriculture land is considered, 38% is degraded. Most of the degradation had occurred in Asia, Africa and South and Central America. The two main causes of degradation are loss of topsoil from water erosion and fertility decline. In Africa alone, 8 million tons of nutrients are lost every year, representing US$ 1.5 billion per year. 14 Annual depletion of NPK (N+P2O5+K2O) per hectare from African soils varies from less than 30 kg/hectare to more than 60 kg/hectare. The excreta from 10 people during the course of a year could return more than 60 kg/hectare to soil, restoring fertility. The effects of soil degradation and loss of fertility on food consumption, agriculture income and national wealth are significant.

Failure to restore soil fertility over the last several decades has been speculated as a cause of reduced nutrient content of North American and British foods. A recent sampling of foods showed 20-40% less calcium, iron, and Vitamins A and C than was the case several decades ago.15 Exactly why this is occurring is not known, but modern agricultural methods do return all nutrients it takes from the land. Conventional agricultural practices consider soil a way station for nutrient uptake by plants, not a viable living organism where plants grow and thrive. Recycling a whole range of nutrients, as well as organic carbon, to the land is needed for a healthy, balanced soil.



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