How Does Caffeine Affect My RMR?

An aerial view of a healthy breakfast spread on a rustic wooden table. A bowl of chia pudding with granola, blackberries, and banana sits next to a cup of coffee and a plate with avocado toast topped with a fried egg.

America loves coffee. Over half of America’s adult population relies on that heady combination of aroma and caffeine to jump start each day. But what exactly does that first cup o’ joe do to your metabolism?

We decided to find out it by running some pre-coffee and post-coffee resting metabolic rate (RMR) tests on ourselves!


To test this out, Elaine:

  1. Ran two regular, fasted, RMR tests to establish a baseline
  2. Chugged a Starbucks grande cold brew with no cream or sugar
    • This is roughly equivalent to 200 mg of caffeine
  3. Waited 45 minutes after which 99% of the ingested caffeine should have been absorbed
  4. Ran three more RMR tests to measure the changes

All told, our simple testing procedure took roughly two and a half hours.


Here are Elaine’s results:

TimeResting Metabolic RateHeart Rate
08:34 AM159868
08:49 AM162768
Drink Coffee!
09:53 AM185861
10:13 AM193064
10:33 AM188667

On average, Elaine's metabolism increased by about 17% after drinking the coffee!

For any individual, the magnitude of the impact of the caffeine on RMR will vary depending on:

  • Dosage of caffeine
  • Body mass of the individual
  • Sensitivity to caffeine
  • Other factors

In this case, Elaine is a 5’ 3” woman who does not normally drink coffee, so she was fairly sensitive to its effects. She was certainly jittery afterwards.

Generally, this effect will last about 1-3 hours. This is why we require our clients to abstain from coffee for at least 4 hours before the RMR test. Of course, using the caffeinated RMR as a baseline for nutrition planning is not advised, as it could lead to inaccurate calorie planning, and consequently, unintended results.

Curious about the speed of your metabolism? Sign up at our storefront in SoCal or at one of our RMR truck events in NorCal - and don’t forget to skip the caffeine that morning!

Recommended articles
A woman in jeans and a green shirt lies on a medical machine, smiling slightly. The machine is light gray and has a visible laser warning sticker. This is a DEXA scan for bone density or body composition.
02 Feb
3 mins read
Radiation, DEXA Scans, and You
A woman in a black swimsuit measures her waist with a pink measuring tape.
14 Aug
3 mins read
Comparing Body Fat Testing Methods
Water is being poured from above into a clear glass, splashing and filling the glass against a light blue background with water droplets on the surface below.
04 Oct
3 mins read
Will Drinking Water Affect My Scan?