[Reading Science] Is It Healthy to Feel the Urge to Poop Right After Eating?

There are people who feel the urge to defecate immediately after eating. Is this person someone who digests well and is healthy?
Photo by YouTube screen capture

[Asia Economy Reporter Kim Jong-hwa] Sometimes, after enjoying a hearty meal with family over the weekend, you may feel an immediate urge to have a bowel movement. Does this mean that the food you just ate has already been digested and is signaling your body?

Bowel movements are very important. All living organisms must excrete waste to survive. Humans have both urination and defecation. Urination occurs frequently, about 3 to 5 times a day, while defecation usually happens once or twice a day, and sometimes only once every few days.

In such cases, when you suddenly feel the need to defecate right after eating, many people think, "Digestion must be really fast," or "The food I just ate must have already been digested." Is this thought correct?

The immediate urge to defecate after a meal is not a signal that the food just eaten has been digested. It takes about 16 to 30 hours for food to be digested and turned into stool. This is a relatively long process. If you feel the urge to defecate right after eating, that signal is actually coming from food you ate yesterday or the day before. In other words, it is from food consumed at least 16 hours earlier.

When food enters the mouth, it undergoes mastication, where it is crushed and mixed with saliva containing digestive enzymes, then passes down the esophagus. The esophagus moves food to the stomach through muscular movements, taking about 30 seconds to reach. Once in the stomach, the food mixes with gastric juices and continues to be churned until it becomes almost liquid; this digestion process in the stomach takes about 4 to 6 hours.

The digested food then moves to the small intestine, which is 5 to 6 meters long. The villi in the small intestine absorb nutrients over 5 to 7 hours. The remaining residue moves to the large intestine, which is about 1.5 to 1.6 meters long, where water is absorbed. This process takes about 10 hours.

Once the residue, now dehydrated, accumulates sufficiently in the large intestine, it is finally expelled as stool. Even for people with fast digestion, it takes about 16 hours before stool can be excreted. Therefore, an immediate urge after eating signals that dehydrated residue has accumulated in the large intestine, not that the food just eaten has been digested.

Bowel movement frequency varies from person to person, and even for the same individual, the timing can differ. Differences in personal eating habits and digestive ability affect this, but also the digestion times of various nutrients in food differ. For some, it takes 16 hours, while for others it can take up to 30 hours for food to be excreted as stool, nearly twice the time, due to these reasons.

For example, 100 ml of milk consumed every morning contains about 3 grams of protein. Of this, 20% is whey protein and 80% is casein protein. Whey protein is digested in about 15 to 30 minutes, but casein protein takes 2 to 8 hours to digest.

Villi inside the small intestine. These villi absorb nutrients from the digested food.
[Photo by YouTube screen capture]

Water digestion time also varies depending on the nutrient type. Plain water, when the stomach is empty, passes through the stomach without delay. Sports drinks or juices are absorbed within 15 minutes, but absorption time varies depending on the type of fruit juice. Juices with soft pulp like orange, grape, or grapefruit are absorbed in 20 to 30 minutes, while those with firmer pulp like apple or pear take about 40 minutes.

In other words, the harder the food consumed, the slower the digestion speed, and people with indigestion or weak stomachs generally take longer.

People who feel an urge to defecate immediately after every meal are likely to have "Irritable Bowel Syndrome" (IBS). This condition involves insufficient intestinal motility, leading to improper digestion, and sometimes food eaten just moments ago is expelled as stool without proper digestion.

IBS can be triggered by stress or overeating and is one of the most common digestive disorders, affecting about 7 to 15% of the global population. Although severe abdominal pain may occur, symptoms usually disappear after bowel movements, and it is not life-threatening. However, if symptoms persist for years, it is advisable to seek treatment.