When is the best time to measure body fat?

If you measure body fat regularly, this might have happened to you before - you step on a body fat scale in the morning and find out that your body fat is higher than it was last night, and feel disappointed at the lack of progress. But you measure once more in the evening, and see that the body fat number if lower, and feel confident that your hard work exercising is paying off.

What’s going on, and what’s the actual truth? Is your body fat actually different in the morning compared to the evening? Is there a time of day that will give me the most accurate result?

What’s the source of body fat fluctuation?
Morning: your body weight tends to be lowest at this point. However, before measuring body fat, you should drink a glass of water and go to the bathroom first, because the temporary hydration you feel when just waking up will actually increase bioelectrical impedance and give you a higher body fat result.

Evening: after a day of food and activity, your body weight will be highest, but it’s hard to predict how bioelectrical impedance is affected by your activities. A full day of manual labor will affect your body differently compared to a sedentary day! Therefore it’s not the best idea to measure body fat in the evening, as there are just too many variables affecting accuracy.

Let’s imagine someone who normally weighs 50 kg and has a “true” body fat of 25%, and how these measurement results may fluctuate depending on the circumstances.

  • She measures right after waking up. Weight 50 kg, Fat 25.5% (slight dehydration)
  • She drinks some water and takes a quick shower before work. Weight 50 kg, Fat 24.5% (body temperature increase, hydration recovering to normal)
  • She goes to exercise after work, and measures herself before dinner. Weight 49.5 kg, Fat 23.5% (body temperature increase, increased circulation after exercise)
  • She measures at night before bed and a day of activities. Weight 51.2 kg, Fat 24.1%

From the example above, we can observe that the body fat result provided by a body fat scale (or rather, by any body composition analyzer) is not a static number, but rather one that can be affected by various activities throughout the day, including eating, drinking, exercise, going to the bathroom, sleep, and other factors. For consumer-grade products, a range of around 2% is fairly normal.

So when is the best time for measurement?
Measurement in the morning will be most accurate, because you don’t have to worry about the effect of food, drink and activities on bioelectrical impedance. (just make sure it’s not immediately after waking up, when you will be slightly dehydrated)

But if you can’t do it in the morning for whatever reason, the second key is to make sure you measure at a consistent time of day, and make sure you control as many variables as you can. This will still allow you to track trends in body fat and other results long-term, which is the primary purpose of body fat scales!

It’s important to recognize that tracking body fat isn’t to pursue a certain goal per se, but rather to observe improvement or backsliding. So long as you keep up a healthy active lifestyle, you will see improvement which will be reflected long-term using your device!