How Are Water and Other Fluids Digested In The Human Body?

Water and other fluids follow the same journey as other types of food, but in their case, the process involves absorption, rather than digestion.

We know that the food we eat goes straight down our esophagus (a.k.a., the food pipe) and into our stomach after we’ve swallowed it. We have already covered the entire journey of food, starting from when it enters the mouth and ending when it is excreted from the body, in this article.

However, we’ve recently had several readers ask us what happens to water and other fluids, like tea, coffee, alcohol and other beverages that we regularly consume. Do they follow the same route as the ‘solid’ food, or do they have a different, quicker route for digestion, primarily because they’re liquids?

Lots of water in our gut

Humans typically consume around 2 liters of dietary water on a daily basis through various means, including drinking water directly or via food and other beverages. Additionally, the volume of gastrointestinal secretions (including gastric, salivary, pancreatic, intestinal and biliary) amounts to around 8 liters, which means that 10 liters of fluids enter the intestines every day (Source). That’s quite a significant amount of fluid to be processed—or more specifically, absorbed—within the body.

When talking about digestion/absorption of the stuff that we consume, the first thing you should always remember is that everything we eat goes to the stomach through the same route—the esophagus. Liquids like water, tea and alcohol do not take a different route.

that-water-has-a-different-route-to-reach-the-stomach-meme

The initial digestion stage is akin to putting your entire meal (liquids included) in a blender. Just as in the blender, everything we consume gets mixed together and forms a gooey mess inside the stomach. However, just so you know, the breakdown of the food begins before that, when it is inside the mouth itself. Our teeth pulverize the food mechanically, while the saliva present in the mouth chemically breaks down fat and starch. This happens for solid foods that contain large complex molecules, such as proteins and carbohydrates.

Absorption of water molecules

Water, on the other hand, is a very simple molecule, so our body doesn’t have to break it down into smaller, simpler molecules. As a matter of fact, water molecules are so small that they have no problem diffusing through the cell membrane of human tissues. This cell membrane consists of small channels or pores through which water and ions, like sodium, passes inside the cell, meaning that water is directly absorbed through the epithelial cells that cover humans’ intestinal tract. In short, this means that the small intestine is responsible for absorbing of most of the water that we consume.

The role of the small intestine in the absorption of liquids

Fortunately for us, the small intestine is more than up to the task. It’s quite an extensive organ, boasting a length of around 20 feet (6 meters). It also has a huge inner surface area of roughly 250 square meters—the size of a tennis court! (Source) This large surface area helps in the quick and efficient absorption of water and other fluids.

Of the almost 10 liters of water that enter our stomach every day, 80-90% is absorbed by the small intestine. The remaining 10% (amounting to 1 liter of water) is passed on to the large intestine, which reabsorbs as much water as it can from the waste materials that are ready to be excreted out of the body as fecal matter.

Absorption of other liquids

The non-water fluids that we usually consume on a daily basis are nothing but chemicals suspended in water. Fruit juice, for example, mostly consists of water and sugar, along with several other ingredients, like preservatives, vitamins and minerals in small quantities. The sugar will get broken down by enzymes in the mouth and the small intestine, where they will also get absorbed into the body. The vitamins may or may not be broken down, but will eventually be absorbed in the small intestine; the same goes for the minerals.

For drinks like tea and coffee, it is a similar process. The sugar and fat, if milk is used, will begin its breakdown in the mouth. The stomach will churn everything, and begin to break down proteins, again from milk that might be present. Once the food reaches the small intestine, the vitamins and minerals will be absorbed. Teas and coffee also contain chemicals classified as antioxidants, some of which might be absorbed into your body. Amino acids are also a part of tea and coffee, and they meet their absorbed fate in the small intestine.

When alcohol (ethanol) is consumed, it first enters the stomach, where it can be absorbed into the bloodstream. If there is food already present in the stomach, the absorption of alcohol into the bloodstream slows down considerably, as it can’t be moved to the small intestine immediately. On the contrary, if one has alcohol on an empty stomach, the absorption of alcohol into the bloodstream takes only a few minutes.

However, alcohol absorption is linked to other foods as well. Eating a high-fat or protein-filled meal before drinking decreases alcohol absorption. One reason is that eating such food delays the transition of food from the stomach to the small intestine, something called gastric emptying. Scientists still debate this, as the exact reason and mechanism are still unknown.

All in all, everything that we consume in our diet is broken down to its bare constituent molecules through digestion. Therefore, it doesn’t matter whether you’re having a sumptuous meal or a simple glass of juice; everything is treated more or less the same way after it has been ingested.

References

  1. Vivo Colostate
  2. The University of New Mexico
  3. The Alcohol Pharmacology Education
  4. Canadian Medical Association Journal
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Ashish is a Science graduate (Bachelor of Science) from Punjabi University (India). He spends a lot of time watching movies, and an awful lot more time discussing them. He likes Harry Potter and the Avengers, and obsesses over how thoroughly Science dictates every aspect of life… in this universe, at least.

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