T Nation

Dehydration and BF%

Hey All,
I got a quick question. How much of a factor does dehydration play in determining one’s %BF? Does one get a lower reading if he/she is hydrated? Or does one get a lower reading if he/she is dehydrated? Thanks…Tony G

A few random thoughts:

  1. Yes, in a broad sense. Less water=less fat free mass (FFM). Less FFM with fat mass (FM) held constant equates to a higher BF%, even though there was no actual fat gain.

  2. As for “readings,” it depends on what methods you’re utilizing. In bioelectrical impedance, dehydration will definitely affect the result. Water is a good conductor of electricity, so less water leads to slower conduction, and an elevated FM reading.

  3. Check out Jason Norcross’ “Body Composition for Beginners” (parts 1 and 2) for more info on the advantages and disadvantages of various methods.

Hope this helps.

Tony -

It depends on the method more than anything. Bioimpedance and hydrostatic weighing will be affected more than skinfolds.

Sorry peoples…I am referring to electrical impedance when I ask this question.