Episode 149 – Does Coffee Actually Dehydrate You?

Key Topics Covered

The simple logic is that since caffeine is a diuretic (increases urination), then coffee is something that dehydrates you. However, there are a lot more layers to this, which we will cover in more detail.

Research Supporting the Diuretic Effect

  • A meta-analysis on this topic involving 16 studies found  that consuming an average of 300mg of caffeine and in the form of an average of 710ml of coffee increased urine production by 109ml in comparison to drinking non-caffeinated beverages.
  • This could be interpreted from 3 perspectives:
  • One is that the diuretic effect is real. 
  • The second is that it’s debatable about how practical or relevant that is.
  • The third is that the 109ml amount is quite small in comparison to the 710ml of coffee. The coffee overall clearly had a net hydrating effect. 
  • Keep in mind these are just averages, but I think it provides a good overview of the research.

Habitual Intake

  • A lot of caffeine research is skewed by habitual vs non-habitual intake.
  • Often participants will be withdrawn from caffeine for a period of time OR are just people who don’t consume caffeine. 
  • This allows for an accurate assessment of the impacts of caffeine. But it also makes some research irrelevant for regular consumers.
  • The consensus is that this diuretic effect significantly decreases if you drink coffee regularly.
  • A study looking at this got 50 habitual consumers to consume either 800ml of water or 800ml of coffee (4mg/kg) in addition to their habitual fluid intake (which was provided as water and had been measured in the lead-up). There was no difference in urine production.


  • We could go even deeper into the research, but no matter how you look at it:

Coffee, tea, and other caffeine-containing liquids still count towards hydration. Maybe you need a bit more liquid because of the small diuretic effect. But the effect is small and they certainly don’t dehydrate you.

  • However, this would scale based on fluid content – for example, espresso vs large flat white.

Relevant Blogs / Resources

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