Why Your Feces Have Those Color

Did you know that the delicious burgers you have in your hand will become nutrients as well as waste products? To be candid, there are also foods that we eat that are more of waste and less of nutrients. By digesting food, the body breaks it into different types of nutrients and waste products. We will be looking at the waste part of it in the post, and not the nutrient part of it.

As undigested remnants of food make their way from the stomach to the colon, they undergo a transformation into what we recognize as feces. This metamorphosis is made possible through the rhythmic contractions of the intestinal walls, which extract water from the waste materials. Additionally, a community of bacteria plays a crucial role in the final stages of digestion. These bacteria aid in breaking down complex food molecules, releasing methane and ammonia gases, notorious for their pungent and disagreeable odor, which can enhance the scent of the departing waste which is the feces.

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In the breaking down of proteins in the body, sulfur compounds such as hydrogen sulfide are released. The byproduct from protein breaking down has a rotten egg smell. For fat, the breaking down can produce short-chain fatty acids which releases the pungent smell you get in feces. Now that the cause of fecal smell has been identified, how do feces get its color.

The lifespan of a red blood cell is approximately 120 days. Upon their natural demise, they undergo a process known as hemolysis, giving rise to a yellow-orange pigment. This byproduct is subsequently transported to the liver. The bile, a digestive fluid stored in the gallbladder and produced by the liver. The yellowish-green or dark greenish-brown hue of bile results from bilirubin, a vital component responsible for digesting and absorbing fats.

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When we consume fatty foods, the gallbladder contracts, releasing bile through the bile duct into the duodenum. Bilirubin is also released into the intestine, where intestinal bacteria act upon it, breaking it down into a brown pigment. It is this transformation that imparts the characteristic brown color to our feces.

In the intestine, some of the Bilirubin is converted to urobilinogen by intestinal bacteria, and some are reabsorbed by the bloodstream which is then excreted by the kidney via urine which then gives urine its yelllow color. The color of feces can differ, depending on the amount of bilirubin in the intestetine and how it interacts with other components in the digestive system. Food type can also determine the color of feces as they affect the production of bile and the metabolizing of bilirubin.

Notably, certain dietary choices can give rise to alterations in fecal color, while foods like garlic and onions, containing sulfur compounds, may be absorbed into the bloodstream and subsequently excreted in feces, intensifying their odor. Diets rich in fiber can lead to the production of larger, softer stools by promoting the movement of stool through the digestive tract and supporting the growth of gut bacteria, which can impact fecal odor.

Our feces' color, odor, and consistency are influenced by a variety of factors, including our dietary choices, hydration levels, medications, gut microbiome, and overall health. These multifaceted aspects collectively contribute to the unique characteristics of our waste products, reminding us of the intricacies of the human digestive system.

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Reference

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https://www.hsph.harvard.edu/nutritionsource/carbohydrates/fiber/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7215946/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8006275/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6040266/
https://microbiomejournal.biomedcentral.com/articles/10.1186/s40168-019-0704-8
https://www.sciencedirect.com/topics/medicine-and-dentistry/urobilinogen
https://www.ncbi.nlm.nih.gov/books/NBK470290/