Biology Forum Physiology drink water, orange juice or Cola before eating?

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    • #5530

      Any biology book will tell you that it is not good to drink water before you eat because "gastric juice is dilluted and digestion will be harder". What does that mean? The enzyme quantity is the same, isn’t it? why does the extra water count?
      Few people can actually reason through it if you ask me. According to my own opinion, there are 2 things that contribute to this:
      1. pepsin has an optimum pH around 2-3; the adding of water will increase the pH from 2 to 4-5(depending how much water you drink, of course)
      2. the extra solvent will decrease the rate of the substrate molecules hitting the enzyme molecules.

      Ok, now the pH of Cola, according to them, is 2.71. When i measured myself, i got 2 on the nose. The pH of orange or lemon juice can be even lower, about 1.5-2.

      My question is, is number 2 enough to actually make a difference or because the pH is so close to that of the gastric juice your digestion will be ok.

    • #53700

      I definately understand where you’re coming from. I like the hypothesis. I definately think that different substances you drink before eating would have an effect on digestion. Even a small difference in pH can mean a big difference in digestion. The enzymes responsible for digestion may have similar pH numbers to the consumed substance, however the purpose of the enzymes can be completely different.

    • #53811

      Hmmm…..what I think is like this…
      Drink water before eating of while eating have either good and bad effect. If you drink it too much, well, as you’ve said…it will raise the pH of gastric juice thus lowering the optimality of pepsin enzyme. Beside, by the raised pH, it’s also possible to have some pathogenic bacteria which don’t killed by gastric juice.
      If we don’t drink before eating, it will be hard for us to swallow the food…it’s too "dry" in esophagus.

      Second, how about cola…well, based of the cola’s pH, it’s possible for us to get our pH lowered to 1.5 – 2….but remember that the thing that makes cola become acidic is carbonic acid, H2CO3 which will get dissociated into H+ and bicarbonate ions…which then, will get dissociated again into CO2. I think that, by excessive amount of CO2 is not good for our somach, especially before eating because there’ll be a pressure difference which indirectly affect the diaphragm and causing "hiccups"…"lol"

      But, I don’t think that the pH of cola is about 2…wow, it’s about 100 times more acidic compared to vinegar….
      Oh, any info about the sucralose (chlorine derivative from sucrose) which is used in cola?? "mrgreen"

    • #53836

      I was thinking about what you said victor. When i measured the pH however, and i got 2, i said "Hey, even if i got it wrong and it is about 3, it is still much more acidic than mineral water which has a similar CO2 concentration according to my tongue CO2 detector 😀 "
      After some research, i realised that Cola contains H3PO4 which actually gives it’s incredible acidic pH. So i did an experiment: shaked all the CO2 out of the Cola and then measured the pH. Still somewhere between 2 and 3. So the H2CO3 has only a minor contribution.

      About the fact that the esophagus is too dry if you don’t drink some water. Well, the esophagus mucose membrane secrets mucus. But it depends on what you eat. If you eat raw flower, yeah, you should drink some water with it :d

    • #53893

      ahhh.. now i know, ty!

    • #89515

      I didn’t see he asked for the aphrodisiac drug 🙄

      When I read the question, I immediately thought that too much water may increase the gastric volume thus making digestion slower, but then I realized what if the situation is depending on our health conditions? what if certain people with metabolic alklosis or acidosis conditions have to be watched for the type pf food that they eat since it might alter also their acid-pH balances? well, just an idea 😉 .

    • #89520

      lindow 195 must love aphrodisiacs!

      Have you heard of what?!
      Watch it MrMistery.

    • #89527

      I see that many really like to open up other topics huh? 😉

    • #89535

      sorry about that. Just spam that went unnoticed.

    • #89854


    • #91066

      Any biology book will tell you that it is not good to drink water before you eat because "gastric juice is dilluted and digestion will be harder". 🙄

      ??? Where ARE these s***ty textbooks, I’ve NEVER seen this. This is nonsense.

      The FACT is, if your stomach acid is diluted by food or drink, IT JUST MAKES MORE.
      Your stomach is not a passive beaker in chemistry class – it is a living organ and it adjusts to its environment.

    • #106317

      and i think it should also depend on the person himself, how he feels.. if drinking water with meals, before meals, or after meals is not harmful for him then everything is ok )

    • #107184

      It is a complete untruth that you should not drink water with a myth. It is an urban myth that was started that has no factual basis. If you drink water, the stomach has the ability to detect pH. The actual process is much more complex mechanically, but that doesn’t need to brought into the discussion. Pepsin is the active form of a protein called a zymogen which is enzyme that has to be cleaved to be activated. Pepsin as well as other enzymes (enzymes are all proteins but not all proteins are enzymes) such as trypsin start off with -ogen at the end of their name. Pepsinogen and trypsinogen. They are cleaved by the hydrochloric acid secreted by parietal cells in the stomach to pepsin and trypsin (both secreted by chief cells).

      Regardless of acidity in the stomach, the acid is neutralized in beginning by bicarbonate because the acid will damage the enyzmes and the lining of the intestine. Now, only in specific cases such as chronic heart burn or ucler conditions will acidity be a problem. There can also be problems with not secreting enough acid in some individuals. Only found in the elderly but relatively not frequent. For the most part, people do not have a problem secreting enough acid into their stomach. Drinking soda and juices can just add to unwanted many calories in the diet for some people.

      If you withhold water during a meal, the stomach has to make more mucus and water into the stomach which can be a major problem for those that suffer hypertension and other blood volume conditions. The stomach cannot mix properly if it does not have the fluidity to mix problem. You can try this by eating a very heavy fatty cake where the water will not mix with the fat (trust me it doesn’t feel good). The enzymes in the intestine have to find their destination in the food in order to breakdown the food that you have consumed. If you have a nice "dry" stomach, where everything is really super viscous your enzymes will not find what they are looking for as easily and will result in improper digestion. This can result in digestive problems further down the line. Now, there is some validity to not drinking as much water because it might slow down stomach emptying and as a result keep you full longer. This is advantageous in those that want to lose weight by doing less snacking.

      The moral of this story… drink water with your meal or any other beverage in moderation (not too much and not too little) because your body is extremely adaptive. Unless you have instructions from your physician or evidence to say that you have an acid secretion problem, don’t worry too much and enjoy your meal. Like others have said, try eating without a drink and its quite hard.

    • #107757

      not all enzymes are proteins, e.g. the ribozyme is RNA
      trypsin is not cleaved by HCl since it is not in stomach
      why should be the acid neutralized? Where does the bicarbonate come from?

    • #114808

      While I see this thread is very old, I came across it while researching something about diet and pH. I agree that drinking while eating can adversely affect the digestive process. Additionally, drinking carbonated beverages brings other factors into digestion. When the carbon dioxide enters the stomach, the pyloric sphincter (which is closed while the first stages of digestion occur in the stomach) opens in response to the increased pressure from the CO2. This causes the contents of the stomach to empty into the colon in the less-digested form and also the CO2.

      As most people know, CO2 is a waste product which the lungs expel in exchange for the much-needed oxygen supply into our body and ultimately, our cells. This helps keep our blood gases balanced, and the premature emptying of CO2 in this manner causes it to directly enter the blood stream, adding a burden to the body’s natural detoxification process. In short, we are drinking a substance infused with something our body eliminates as waste.

      Another thought to consider is that soda is pretty much CO2, water and syrup. The chemical mix of CO2 and water is carbonic acid. The acidifying result of such a mixture places more stress on the body to maintain the narrow pH range of 7.35 to 7.45 required to sustain human life

    • #114820

      can you show your resources?

      1) urine composes of more than 95% water. Does that mean we should avoid drinking water, because it’s a waste?
      2) and how do you think that is the CO2 transported from the cells to lungs? Could it be directly through blood?
      3) pH of stomach fluids is something around 2, even Coke is basic in comparison with that.

    • #115293

      Drinking too much cola is not good for health. Because it contains phosphoric acid which reduces the bone density and also the reason for chronic kidney diseases. Drinking citrus juices is good for health, because it contains lot of vit C. I think if pH increased due drinking of water, there might be some sensing mechanism which ultimately lead to more acid production by parietal cells. Another possibility is that excess water is rapidly absorbed to the blood or passed to the small intestine.

    • #116274

      I got no notification on your request for a source and happened across my post here with your inquiry – my apologies for the delay in responding. Here are sources which should address your inquiry:

      This first link discusses the emptying of stomach contents in response to carbonation:


      This second link discusses the function of the lungs in exchanging oxygen for CO2 in the blood:

      http://www.merckmanuals.com/home/lung-a … on-dioxide

      This final link is a simply-stated presentation of health effects of high blood CO2 levels:


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