6 ms·

"Don't swim for 30 minutes after eating, you'll get cramps and drown" is one I've heard in the US from multiple people

jaggederest 5y ago
"Hydration", or "8 glasses of water a day" is another one. Your kidneys work, if you aren't thirsty (barring certain medical conditions) you don't need to drink water. There's no such thing as "dehydration without being thirsty" on a routine basis. You'll develop a pretty powerful thirst at 2% water depletion, and for most healthy adults you need to see 4% or more for negative effects.
- deleted 5y ago
  [deleted]
- Nasrudith 5y ago
  Drinking a lot of water can be helpful - if you expect to perspire heavily from temperature and/or physical exertion but that is a different kettle of fish.
  - russdill 5y ago
    It can be very difficult communicating people new to the Phoenix area just how much water they need to drink during the summer if they are going to exert themselves outdoors.
    - BrandoElFollito 5y ago
      I am French and travelled menu times to Phoenix for business. I loved the place (Scottsdale) and was once invited to play golf there (my first golf experience). I was slowly turning into lyophilized me, fortunately I could give up at the 9th hole and went to immediately drink 2 liters of water.
  - nradov 5y ago
    Drinking a lot of water prior to exertion isn't helpful. You'll just piss it out.
- tibbetts 5y ago
  I’m not an expert, but 20 years ago I had a small part in DARPA research into monitoring soldiers’ hydration. The idea was that people in combat often don’t notice they are thirsty, or power through it, and as a result are operating at reduced cognitive and physical capacity. Of course, that’s combat. And for all I know the funding was based on the popular misunderstanding.
  - jaggederest 5y ago
    Yes, and marathon runners or other people in extreme situations need to drink before they're thirsty so that they keep their intake high enough. But those are really extreme situations, most people walking around with a water bottle aren't sweating out 2 liters per hour.
- sonicggg 5y ago
  Nonsense. As we age, our sense of thirst diminishes. Senior citizens are at higher risk of dehydration. https://health.clevelandclinic.org/drink-up-dehydration-is-an-often-overlooked-health-risk-for-seniors/ https://health.clevelandclinic.org/drink-up-dehydration-is-a...
  - jaggederest 5y ago
    That's true, and that's why I said "healthy adults" - Senior citizens are in a special category where they may need to drink before they are feeling thirst, but most people are not senior citizens (yet?). The average person walking around with a water bottle doesn't need to drink before they're thirsty.
    - waste_monk 5y ago
      Is there such thing as a "blood hygrometer" (for lack of a better description) that could objectively tell you when you're dehydrated?
      - mattkrause 5y ago
        Dehydration skews a lot of blood values. Hematocrit is probably the most direct, since it's the percentage of red blood cells in a volume. Dehydration decreases the volume, and thus increases hematocrit. Electrolytes get out of whack too. In practice, I don't think anyone really does this: thirst, urine/sweat, and weight are very easy to measure, and the obvious next step would be pulse or blood pressure.
        waste_monk 5y ago
        I was thinking more along the lines of whether there is something like a continuous glucose monitor but for dehydration, which could beep or otherwise alert a semi-independent elderly person that they are becoming dehydrated so they could get some water before it started to stress their kidneys. Like those pill boxes with alarm clocks built in so they don't forget to take medication. But I'm aware there are various issues with CGM's (a friend has one, which may act as an insulin pump as well, and complains that the needle needs to be moved around every so often as the attachment site stops giving accurate readings). The cost/benefit probably isn't there, if an elderly person cannot control their own hydration they probably also aren't able to adequately care for a CGM or similar monitor. If it was something you could implant into the body and poll wirelessly it might have some value.
jh3 5y ago
Now that I have my own children, I'm convinced this myth is a delay tactic perpetuated by parents :)
- lhorie 5y ago
  Yep, white lies. The underlying rationale is that kids do throw up in pools and you don't want to get into a public argument with a kid about how they're not going to throw up, can they go in pretty please. It's like the thing about getting arrested for turning on the lights inside a moving car. No, you won't get arrested, but the reflection on the windshield can be annoying, and getting distracted by kids going ham on flicking the lights on and off is obviously dangerous. See also, school "permanent records".
  - the_af 5y ago
    I think the white lie is even simpler. As a kid, I always wanted to go swimming (swimming pool or sea) as soon as I finished eating. My parents told me not to because of the cramps. "You must wait an hour before swimming". It wasn't about throwing up and as an adult I finally understand it: they wanted to have a chat at the table after eating, take it slowly, maybe they were a bit drowsy. What they didn't want to do was to look after kids doing potentially dangerous activities such as swimming. So that hour of waiting? A period of grace for them to enjoy their meal and maybe rest for a short while.
    - jh3 5y ago
      Exactly! Parental relief.
    - lhorie 5y ago
      Nah, it's definitely the hygiene thing. Pools often forbid food and drinks at the deck for the same reason: if someone dirties the pool water, they basically need to close off the whole pool and recycle the pool water for a few hours, which is super inconvenient for all parties involved (and obviously embarrassing for the parents of the kid who made the mess). You'd be surprised at how often these things happen. Ask me how I know :)
kazinator 5y ago
Even if wrong, it seems harmless enough. Even if I believed that, I wouldn't, say, avoid jumping out of a burning ship into the water just because I just had a meal.
Tijdreiziger 5y ago
I'm from the Netherlands; I always heard that's because you might get a bit too excited and throw up your food. The 30 minutes are to allow your stomach to settle a bit.
hinkley 5y ago
I don't recall the original interaction anymore but I remember confronting my mother in my early 30's about her telling me the one about gum staying in your stomach for 7 years. She had no recollection of having done that, and argued that being a nurse she would have never told us that. But apparently younger me was convinced that story came from her and not from the schoolyard rumor mill.
analog31 5y ago
An amusing thing about such myths is that instead of abandoning them outright, we wrap them in auxiliary myths such as not wanting kids to throw up. On the other hand, how long does it take to know that your kids haven't gotten food poisoning from the food that would be served near a swimming pool?
- mattkrause 5y ago
  It's presumably not just food poisoning--it'd be exercise-induced.

"Hydration", or "8 glasses of water a day" is another one. Your kidneys work, if you aren't thirsty (barring certain medical conditions) you don't need to drink water. There's no such thing as "dehydration without being thirsty" on a routine basis. You'll develop a pretty powerful thirst at 2% water depletion, and for most healthy adults you need to see 4% or more for negative effects.

deleted 5y ago
[deleted]
Nasrudith 5y ago
Drinking a lot of water can be helpful - if you expect to perspire heavily from temperature and/or physical exertion but that is a different kettle of fish.
- russdill 5y ago
  It can be very difficult communicating people new to the Phoenix area just how much water they need to drink during the summer if they are going to exert themselves outdoors.
  - BrandoElFollito 5y ago
    I am French and travelled menu times to Phoenix for business. I loved the place (Scottsdale) and was once invited to play golf there (my first golf experience). I was slowly turning into lyophilized me, fortunately I could give up at the 9th hole and went to immediately drink 2 liters of water.
- nradov 5y ago
  Drinking a lot of water prior to exertion isn't helpful. You'll just piss it out.
tibbetts 5y ago
I’m not an expert, but 20 years ago I had a small part in DARPA research into monitoring soldiers’ hydration. The idea was that people in combat often don’t notice they are thirsty, or power through it, and as a result are operating at reduced cognitive and physical capacity. Of course, that’s combat. And for all I know the funding was based on the popular misunderstanding.
- jaggederest 5y ago
  Yes, and marathon runners or other people in extreme situations need to drink before they're thirsty so that they keep their intake high enough. But those are really extreme situations, most people walking around with a water bottle aren't sweating out 2 liters per hour.
sonicggg 5y ago
Nonsense. As we age, our sense of thirst diminishes. Senior citizens are at higher risk of dehydration. https://health.clevelandclinic.org/drink-up-dehydration-is-an-often-overlooked-health-risk-for-seniors/ https://health.clevelandclinic.org/drink-up-dehydration-is-a...
- jaggederest 5y ago
  That's true, and that's why I said "healthy adults" - Senior citizens are in a special category where they may need to drink before they are feeling thirst, but most people are not senior citizens (yet?). The average person walking around with a water bottle doesn't need to drink before they're thirsty.
  - waste_monk 5y ago
    Is there such thing as a "blood hygrometer" (for lack of a better description) that could objectively tell you when you're dehydrated?
    - mattkrause 5y ago
      Dehydration skews a lot of blood values. Hematocrit is probably the most direct, since it's the percentage of red blood cells in a volume. Dehydration decreases the volume, and thus increases hematocrit. Electrolytes get out of whack too. In practice, I don't think anyone really does this: thirst, urine/sweat, and weight are very easy to measure, and the obvious next step would be pulse or blood pressure.
      - waste_monk 5y ago
        I was thinking more along the lines of whether there is something like a continuous glucose monitor but for dehydration, which could beep or otherwise alert a semi-independent elderly person that they are becoming dehydrated so they could get some water before it started to stress their kidneys. Like those pill boxes with alarm clocks built in so they don't forget to take medication. But I'm aware there are various issues with CGM's (a friend has one, which may act as an insulin pump as well, and complains that the needle needs to be moved around every so often as the attachment site stops giving accurate readings). The cost/benefit probably isn't there, if an elderly person cannot control their own hydration they probably also aren't able to adequately care for a CGM or similar monitor. If it was something you could implant into the body and poll wirelessly it might have some value.

jh3 5y ago

Now that I have my own children, I'm convinced this myth is a delay tactic perpetuated by parents :)

lhorie 5y ago
Yep, white lies. The underlying rationale is that kids do throw up in pools and you don't want to get into a public argument with a kid about how they're not going to throw up, can they go in pretty please. It's like the thing about getting arrested for turning on the lights inside a moving car. No, you won't get arrested, but the reflection on the windshield can be annoying, and getting distracted by kids going ham on flicking the lights on and off is obviously dangerous. See also, school "permanent records".
- the_af 5y ago
  I think the white lie is even simpler. As a kid, I always wanted to go swimming (swimming pool or sea) as soon as I finished eating. My parents told me not to because of the cramps. "You must wait an hour before swimming". It wasn't about throwing up and as an adult I finally understand it: they wanted to have a chat at the table after eating, take it slowly, maybe they were a bit drowsy. What they didn't want to do was to look after kids doing potentially dangerous activities such as swimming. So that hour of waiting? A period of grace for them to enjoy their meal and maybe rest for a short while.
  - jh3 5y ago
    Exactly! Parental relief.
  - lhorie 5y ago
    Nah, it's definitely the hygiene thing. Pools often forbid food and drinks at the deck for the same reason: if someone dirties the pool water, they basically need to close off the whole pool and recycle the pool water for a few hours, which is super inconvenient for all parties involved (and obviously embarrassing for the parents of the kid who made the mess). You'd be surprised at how often these things happen. Ask me how I know :)

kazinator 5y ago

Even if wrong, it seems harmless enough. Even if I believed that, I wouldn't, say, avoid jumping out of a burning ship into the water just because I just had a meal.

Tijdreiziger 5y ago

I'm from the Netherlands; I always heard that's because you might get a bit too excited and throw up your food. The 30 minutes are to allow your stomach to settle a bit.

hinkley 5y ago

I don't recall the original interaction anymore but I remember confronting my mother in my early 30's about her telling me the one about gum staying in your stomach for 7 years. She had no recollection of having done that, and argued that being a nurse she would have never told us that. But apparently younger me was convinced that story came from her and not from the schoolyard rumor mill.

analog31 5y ago

An amusing thing about such myths is that instead of abandoning them outright, we wrap them in auxiliary myths such as not wanting kids to throw up. On the other hand, how long does it take to know that your kids haven't gotten food poisoning from the food that would be served near a swimming pool?

mattkrause 5y ago
It's presumably not just food poisoning--it'd be exercise-induced.