I have read somewhere that it is normal to defecate about once a day. This leads me to think that it takes about 24h for food to pass through the body under normal circumstances.
Now lets say you eat some bad sushi that triggers “the runs” within an hour.
When you then defecate, is it the actual sushi that comes out or is it just the food you ate before the sushi?
Also, how fast could food theoretically go from mouth to anus?
In: 935
As others have already said, food usually takes more than 24 hours to pass through the body, because of two main reasons:
1. The GI (gastrointestinal) tract is very long (30 feet / 9 meters)
2. The movement though the GI tract is extremely slow
The 1st reason is obvious enough, but 2nd in a bit less intuitive. You see, because the main fuction of thr digestive system is the absorption of the nutrients, if you want to apsorb as many nutrients as possible, it is wise to keep the food in the intestines (the part of the GI tract that absorps those nutrients) as long as possible. The mechanism that causes the movement through the GI is called peristaltic movement. It is characterized by the formation of the tight ring that closes the intestines just before the digested food. Then, that ring travells towards the anus and pushes the food forwards. Imanige it like this: fill up a rubber hose with water. Then, form a ring with your fingers at the beginning of the hose and advance your fingers towards the end of the hose. What will happen? The water will shoot out of the hose. Congratulations! You have just imitated the peristaltic movement that happens in your intestines.
However, these movements have to be regulated so our body can absorb as many nutrients as possible. For example, fats and proteins are notoriously difficult to absorb because they take much longer to digest than sugars ( the reason why is beyond the scope of your question, but if you’d like to know more, feel free to ask). Therefore, it makes sense that we would have to slow down our peristaltic movements in order to increase the time spent on digestion, thus increasing the efficiency of the absorption. The speed of peristaltic movement is then regulated in two ways: by hormones and and by nervous system.
The nervous system regulates the speed of peristaltic movement using many reflexes that are “built into” our GI tract. There’s a bunch of them but i’m just gonna mention a few of the big ones
1. The gastrocolic reflex if the ability of the stomach, that just received food, to facilitate bowel movement. By doing so, it helps empty the bowels to make room for the food that just got in the stomach.
2. The ileocolic reflex is the ability of the large intestines that just received food from the small intestines to halt further movement of the small intestines. It does that to stop an overabundance of food in the large intestines because that would lower the efficiency of the nutrient absorption.
3. The renocolic reflex is the ability of the kidneys to completely stop the movevent in the intestines because of some type of trauma such as a kidney stone. The reason for this reflex is poorly explained but it is thought that the damage of the tissue of the kidneys and ureter stop the peristaltic movement in the intestines to prevent further damage, but further research is needed.
Hormonal oversight of the speed of the bowel movement is mainly dependent on the properties of the food inside the intestines. The place that “checks” what the food is made out of is the duodenum, a part of the small intestines that looks like the letter “C” and comes right after the stomach. Depending on the chemicals present in the food, it secretes different hormones that activate different responses in the GI tract. For example, if extremely fatty food comes in the duodenum, it will secrete cholecystokinin (CCK) that will activate the secretion of the bile to help in fat digestion; if the food that comes in the duodenum is very acidic, it will secrete secretin, which stimulates the pancreas to secrete molecules that will neutralize the acidity. It is very important to note, that these hormones also regulate the speed of the peristaltic movement. As we’ve already discussed, fats are difficult to digest. Meaning that we would like to have more time to digest them. Therefore, CCK not only causes the secretion of bile salts that digest fats, but it also slows down the peristaltic movement of the intestines to keep the fats longer in the intestines to digest them properly so they can be ready for absorption.
Now, we’ve finally come to the answer of your bad sushi. When you eat something bad, the first line of defense is actually the taste – if it tastes funny, you probably won’t swallow the bad tasting food. However, some bad food doesn’t taste any different than when it’s edible. Then, the second line of defense is vomiting from the stomach. In a shocking twist, vomiting is not only limited to the stomach, but from further down the GI tract, even up to the point of vomiting feces from the small intestines, which can cause some serious physiological complications such as acidosis. Eww. Thankfully, after the food has passed the stomach, these extreme kinds of vomiting are much more rare than the third line of defense after eating something bad – diarrhea. If the duodenum, or any other part of the intestines, notices the toxins from the spoiled food, it is able to produce massive peristaltic movements that try to expel the toxins as fast as possible. That can even happen in a span of just a few hours. We’ve effectively speedran the digestion process that lasts approximately 48 hours in just a few hours. Note that the spoiled food is the last that exits the bowels because all the food that was eaten prior to the sushi has to leave before the sushi can get to the anus.
Now time for some disgusting talk. Why is diarrhea liquidy, and not solid? It’s because we haven’t given enough time to reabsorb all the water we had in our intestines. Because we expelled the waste in record time after eating spoiled sushi, we’ve sacrificed the time to absorb nutrients in order to protect ourselves. That means that all the water that was contained in the food plus all the water from the digestive juices we have excreted also passed in record time through out intestines. We haven’t given enough time to the large intestines to reabsorb the water.
I know it doesn’t seem like it, but i’ve really tried to keep it ELI5, but this topic is far to complicated to understand without having at least 10 more birthdays. So, if there’s anything that was left unclear, or you want to know more about anything I have written don’t hesitate to ask and i’ll try my best to explain. Cheers.
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