10 interesting facts about poop and the digestive system

... that I learned from reading Giulia Enders' (mostly) excellent Gut: Inside Story of Our Body's Most Underrated Organ
  1. No matter what you eat, poop is almost always some shade of brown because of the breakdown products from red blood cells. It's the same reason why pee is always some shade of yellow.
  2. The bacteria on our tongues help breakdown what we eat and contribute to what we taste. Since every individual has a different composition and amount of different bacteria, no foods will taste exactly the same to two different people. (This in addition to the difference in taste as a result of perception.)
  3. A food's 'aftertaste' is the result of slightly slower acting bacteria living on the tongue that breakdown / release (flavour) compounds after we've already swallowed.
  4. The reason we crave/like sweet desserts after a meal is that they have the practical function of providing the gut with a hit of easily digestible sugars whilst the complex fat and proteins in your dinner are broken down (a process that can take hours).
  5. 3/4 of poop is water. 1/3 of the solids in poop is made up of bacteria (the other parts are 1/3 indigestible plant fibre and 1/3 actual bodily waste products)
  6. You empty 1/3 of your bowel each day. If you've been ill and suffered diarrhoea, it can take three days to fill your bowel and poop normally again. This is called the Three Day Rule. Most people don't wait long enough and worry that their bowels are in worse shape than they actually are.
  7. If a baby is born via a Cesarian section, and therefore not exposed to its mother's (specifically placed) vaginal bacteria on its way out, it'll take the child around 7 years to develop a comparatively 'normal' level and composition of important gut bacteria, making it more susceptible to allergies and asthma in the meantime.
  8. Gut bacteria have a real and direct effect on our mood and behaviour by digesting, releasing or preoccupying different molecules, hormones and neurotransmitters. Look up Toxoplasma gondii and prepare to be scared/amazed.
  9. The brain and digestive system are very heavily and tightly interconnected, and our gut more generally has a strong influence on our mood (see above; everyone at one time or other has been 'hangry'). It might be more accurate to say 'I feel and then think, therefore I am'.
  10. Smell is the only sense that can't be activated when dreaming. Weirdly/paradoxically, it is also the best sense for triggering memories.