what causes percentage body fat to go up if you lose weight?

[garsnem]

We have just started with fitbit and i have lost 2 lbs but my body fat percentage has gone up like 6% and i am confused.

[JenniLacey]

How are you measuring your body fat %? It's very difficult to get an accurate measurement without a trained professional. I don't think it's possible for your body fat to raise 6% in a 2 lb loss or such a short amount of time. Your method of testing is probably very inaccurate.

Aside from that you should be strength training while losing weight to ensure that your minimize lean muscle/tissue loss.

[Caffeine]

I second this.  It can be very tricky to accurately measure body fat.  I would almost immediately think that if there is an increase in body fat percentage, that you are losing muscle mass. I also second strength training, and make sure you're eating well (and enough).  

[garsnem]

thanks for the suggestions...i was actually just taking the reading from the fitbit scale we are using and it was slightly concerning hehe and wasn't sure how it was doin it 🙂

[Dominique]

---

@garsnem wrote:

i was actually just taking the reading from the fitbit scale we are using and it was slightly concerning hehe and wasn't sure how it was doin it 🙂

---

I've been using a Fitbit Aria for 6 ½ months and I've never seen a variation of 6% even during that entire period. On the contrary, I've found body fat % values to be very consistent: the highest variation within a 2-week period is perhaps 1.5%. OTOH, I always use it at the same time of the day, first thing in the morning, after going to the bathroom, thus when my body is least hydrated (I don't drink during the night). If you step in on your Aria at random times of the day, you will likely see bigger fluctuations, as your body is more or less hydrated.

[SunsetRunner]

---

@garsnem wrote:

We have just started with fitbit and i have lost 2 lbs but my body fat percentage has gone up like 6% and i am confused.

---

The best guess I would have is you were dehydrated that day.  Here is a snippet from Wikipedia about how consumer scales calculate body fat:

Bioelectrical impedance analysis[edit]

Main article: Bioelectrical impedance analysis

This section does not cite any references or sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2009)

The bioelectrical impedance analysis (BIA) method is a lower-cost (from less than one to several hundred US dollars in 2006[12]) but less accurate way to estimate body fat percentage. The general principle behind BIA: two or more conductors are attached to a person's body and a small electric current is sent through the body. The resistance between the conductors will provide a measure of body fat between a pair of electrodes, since the resistance to electricity varies between adipose, muscular and skeletal tissue. Fat-free mass (muscle) is a good conductor as it contains a large amount of water (approximately 73%) and electrolytes, while fat is anhydrous and a poor conductor of electric current. Factors that affect the accuracy and precision of this method include instrumentation, subject factors, technician skill, and the prediction equation formulated to estimate the fat-free mass.

Each (bare) foot may be placed on an electrode, with the current sent up one leg, across the abdomen and down the other leg. (For convenience, an instrument which must be stepped on will also measure weight.) Alternatively, an electrode may be held in each hand; calculation of fat percentage uses the weight, so that must be measured with scales and entered by the user. The two methods may give different percentages, without being inconsistent, as they measure fat in different parts of the body. More sophisticated instruments for domestic use are available with electrodes for both feet and hands.

There is little scope for technician error as such, but factors such as eating, drinking and exercising must be controlled[12] since hydration level is an important source of error in determining the flow of the electric current to estimate body fat. The instructions for use of instruments typically recommended not making measurements soon after drinking or eating or exercising, or when dehydrated. Instruments require details such as sex and age to be entered, and use formulae taking these into account; for example, men and women store fat differently around the abdomen and thigh region.

Different BIA analysers may vary. For instance when comparing outputs from a Tanita scale to an Omron Body Logic handheld device, the Tanita scale estimated a 40% higher percentage body fat in college-aged men and a 55% higher percentage in college-aged women when compared to hydrostatic weighing. Population-specific equations are available for some instruments, making them more reliable.[12]

[Strategic]

I am having the same issue. Does anyone know how the Aria™ Wi-Fi Smart Scale actually calculates % body fat?

[Dominique]

---

@Strategic wrote:
Does anyone know how the Aria™ Wi-Fi Smart Scale actually calculates % body fat?

---

As @SunsetRunner wrote, the Aria calculates body fat % with the bioelectrical impedance method.

All I can say is my Aria doesn't exhibit the huge variation in body fat % reported by some people. Here is the measurement history (daily morning values) from Jan-9 to date: