How accurate are electronic body fat calculators?

ju5t1n

My gym has a set of scales which supposedly calculate % body fat. They’re the type where you grip two metal handles for a few seconds and get a print out. Does anyone know how accurate these things are?

estampida

there should be some info on the uncertainty within the manual

at a guess +/- 10%

schweiz

Not Very!

They work by passing a weak electrical current through your body. Based upon the resistance your body imparts on this current, you can estimate how much of the tissue that the current passed through is bone, muscle and fat.

The problem is that the current takes the path of least resistance so with a hand held device, the current goes in one arm, across the chest and back out of the other arm so only the arm and upper torso are measured. With scales only the legs and pelvis are measured.

I'm led to believe that apart from water displacement/underwater weighing and x-ray techniques, the best way of calculating body fat percentage is by a trained person using body fat callipers at defined points on the body.

jgsi

My Tanita BC545 has footbed and hand sensors and is still very very optimistic.
However, over sustained use, one result is that a decrease shown in the % figure does prove that one's fat reserves are being used up! However, if you take one reading once in a blue moon, then the result is pretty useless.

ric/rstsport

they're not. they depend on how hydrated you are!

charlie_potatoes

Ric/RSTSport wrote:

they're not. they depend on how hydrated you are!

So they would show a higher fat% if dehydrated and lower fat% if properly hydrated?
Or the other way around?

estampida

The amount of water in you affects the electrical properties of the human body

and that affects the amount fat measured as per your weight (you weight will change with all that water as well)

ric/rstsport

if memory serves me correctly (and i don't have time to work this out right this second) the more dehydrated you are the lower your body fat% is displayed as (but to clarify, this only affects the estimated body fat% not your actual body fat - it remains unchanged)

ric

danlikesbikes

schweiz wrote:

Not Very!

They work by passing a weak electrical current through your body. Based upon the resistance your body imparts on this current, you can estimate how much of the tissue that the current passed through is bone, muscle and fat.

The problem is that the current takes the path of least resistance so with a hand held device, the current goes in one arm, across the chest and back out of the other arm so only the arm and upper torso are measured. With scales only the legs and pelvis are measured.

I'm led to believe that apart from water displacement/underwater weighing and x-ray techniques, the best way of calculating body fat percentage is by a trained person using body fat callipers at defined points on the body.

+1 on that.

The hand held ones are pretty easy to dupe into giving different readouts. Take your first reading, then run on the spot for 10 seconds knees nice and high drop for 10 pushups and 10 sit ups. Remeasure yourself and you will find with a higher heart rate a completely different reading.

The machines with 4 points of contact two for the feet & two for the hands are better and more accurate but a lot more expensive.

ric/rstsport

the gold standard for body fat measurement in order of accuracy is

1) weighing actual fat mass from a cadaver
2) DEXA
3) hydrostatic weighing
4) using very good metal calipers (Harpenden are probably the best) by a highly skilled technician using between 4 & 8 skinfold sites
5) BIA, which is pretty naff
6) jumping up and down naked in front of a mirror. if it wobbles and it ain't supposed to, you can lose fat mass

note that 2 & 3 are still subject to equipment and technician accuracy

ric

ju5t1n

I think I'll keep hold of my £1 then

schweiz

Wikipedia wrote:

Many of the early research studies showed that BIA was quite variable and it was not regarded by many as providing an accurate measure of body composition. In recent years technological improvements have made BIA a more reliable and therefore more acceptable way of measuring body composition. Nevertheless it is not a "gold standard" or reference method. Like all assessment tools, the result is only as good as the test done. Although the instruments are straightforward to use, careful attention to the method of use (as described by the manufacturer) should be given.

Simple devices to estimate body fat, often using BIA, are available to consumers as body fat meters. These instruments are generally regarded as being less accurate than those used clinically or in nutritional and medical practice. They tend to under-read body fat percentage.

Dehydration is a recognized factor affecting BIA measurements as it causes an increase in the body's electrical resistance, so has been measured to cause a 5 kg underestimation of fat-free mass i.e. an overestimation of body fat.

Body fat measurements are lower when measurements are taken shortly after consumption of a meal, causing a variation between highest and lowest readings of body fat percentage taken throughout the day of up to 9.9%.

Moderate exercise before BIA measurements lead to an overestimation of fat-free mass and an underestimation of body fat percentage due to reduced impedance. For example moderate intensity exercise for 90–120 minutes before BIA measurements causes nearly a 12 kg overestimation of fat-free mass, i.e. body fat is significantly underestimated. Therefore it's recommended not to perform BIA for several hours after moderate or high intensity exercise.

BIA is considered reasonably accurate for measuring groups, or for tracking body composition in an individual over a period of time, but is not considered sufficiently accurate for recording of single measurements of individuals.

The accuracy of consumer grade devices for measuring BIA has not been found to be sufficiently accurate for single measurement use and are better suited for use to measure changes in body composition over time for individuals.

Alex_Simmons/RST

They also suck for amputees