---------- Forwarded message ---------

From: Bryan Johnson <news@bryanjohnson.co>

Date: Sat, Oct 8, 2022 at 2:21 AM

Subject: How much water should I drink?

To: happy xiao <happy@hey.com>


Imagine this scenario. You’re at an acquaintance’s house for a social gathering. There are six of you. Conversation flow is light hearted and touching on a little bit of everything. During a pause, your friend who convened everyone explains that they’ve been trying to drink enough water. To your surprise, your friend turns to you and inquires: “how much water should I drink each day?”

What do you say?

This is one of my favorite thought experiments and interview questions. It’s exceptionally useful for what it reveals.

This is how most conversations proceed:

Person: It’s eight cups a day I think. Lately I’ve been carrying this Hydro Flask water bottle with me everywhere I go. I’m trying to drink more water. It helps but it’s also heavy lol. It's also kind of annoying because I’m always going to the bathroom. But I feel great. So I think eight cups of water is about right. Yeah, it’s eight cups.

Me: how do you know eight cups of water is the correct answer?

Person: That’s what they say. I mean, I feel great.

Me: Who is they? Have you seen any evidence about water intake and health outcomes?

Person: Just what I’ve read online.

Me: ok, let’s try this again.

[I then repeat the thought experiment scenario in full]

Me: What do you say when your friend asks you how much water they should drink each day?

Person: I don’t actually know.

Me: 🏆

Sometimes it takes going through the thought experiment several times before they stumble upon the self awareness that their answer was simply repeating common wisdom they’ve heard or read. Not from first hand familiarity with scientific evidence.

Far from being embarrassing, not knowing is one of the smartest things we are all capable of.

Parroting common wisdom is tempting and easy (“yeah, it’s eight cups a day”); however, it’s also a form of potential self and collective harm.

Discerning to what degree we do and don’t know something is hard. In practice, attempting to carefully discern what you do and don’t know allows us to pierce through common wisdom, tradition, anecdote, social norms, hyperbole, heuristics, tropes, metaphor, and folk wisdom.

After assessing what we may or may not know - the next step is to consider if the question is best addressed by math, science, engineering, human opinion or tarot cards.

Now returning to the thought experiment: “how much water should I drink each day?”

Your response:

I actually don’t know. I don’t even know how much water I drink every day because my intake is inconsistent and I don’t measure it. I haven’t died from dehydration, so that seems compelling evidence that I am drinking enough to survive. Outside of that, I have no idea if my water intake is optimal or not. I’ve heard that eight cups a day is suggested, but do not know if there is any supporting evidence or if other factors such as age, health conditions, physical activity and diet would meaningfully change the calculation.

Now that I’m thinking about this, I wonder, if I feel thirsty, does my body actually need more fluid intake for optimal functioning? Or, is thirst like hunger and there is such a thing as water obesity? As I get older, when things in the body start breaking, does my thirst awareness also change?

What can someone measure to determine if their water intake is optimal? Would a blood or saliva test offer answers? I’m unaware of hydration biomarkers, but maybe they exist?

Given this, my dear friend, it seems perfectly ridiculous that I should offer my opinion regarding something that I know little to nothing about. I am sorry that I cannot be of service to you in your time of need. However, as we sort out the scientific evidence to this question, I can offer to refill your hydro flask while you are away in the bathroom so that I can socially signal to you that I am sincerely interested in your well-being.

Your acquaintances: 🤯 and then 👏





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