Bioelectrical Impedance Analysis (BIA) Error?!


Question: Hello. I am a 21 year old male. I weigh 70 kg (154 lbs) and I am 6'2. I have a lean figure which I like to maintain. 2 weeks ago I took my first ever BIA (Bioelectrical Impedance Analysis) test. I registered as having 4.8kg fat, hence being 6.9% body fat mass. 2 weeks later, despite regular cardio exercise and a diet of small meals and fruit, a followup test on the same machine registered a loss of 1kg muscle and a gain of 1kg fat (my weight was exactly the same). Is there a degree of error to which i can attribute this, or did I really gain fat and lose muscle so rapidly, despite my diet and exercise? I calculate my Caloric intake to be about 2300 kcals a day, factoring in appropriate exercise. Are these machines prone to a certain degree of error? Are there any factors I need to know about? It also registers me as having .8kg less water in my body at the time, which I know to have a lower impedance than anhydrous adipose tissue. Thanks for the answers!


Answers: Hello. I am a 21 year old male. I weigh 70 kg (154 lbs) and I am 6'2. I have a lean figure which I like to maintain. 2 weeks ago I took my first ever BIA (Bioelectrical Impedance Analysis) test. I registered as having 4.8kg fat, hence being 6.9% body fat mass. 2 weeks later, despite regular cardio exercise and a diet of small meals and fruit, a followup test on the same machine registered a loss of 1kg muscle and a gain of 1kg fat (my weight was exactly the same). Is there a degree of error to which i can attribute this, or did I really gain fat and lose muscle so rapidly, despite my diet and exercise? I calculate my Caloric intake to be about 2300 kcals a day, factoring in appropriate exercise. Are these machines prone to a certain degree of error? Are there any factors I need to know about? It also registers me as having .8kg less water in my body at the time, which I know to have a lower impedance than anhydrous adipose tissue. Thanks for the answers!

I read on one website that BIAs have a 4% margin of error, but can register errors as high as 15%.
All a BIA does is measure how fast your body conducts a current. A lot of things affect this: level of hydration/dehydration and level of electrolytes are very key. Dehydration and an electrolyte imbalance can definitely screw up a BIA measurement!

BIAs can offer a sort of estimation of body fat, but a very rough one at that. A much better way to get a good body fat measurement is to have a professional measure it using a "pinch test" with calipers. You can often find a person who can do this at your local gym/fitness center. Make sure the person knows what they're doing, as human error in this test can also be as high as 10%.

side note: he DID mean 2300 kcals. "Calories" with a capital "c" means kcals, so...
2300 kcals = 2300 Calories = 23,000 calories.
When we refer to calories in a food sense we always use Calories as standard (notice the capital C in Calories on nutrition labels). The difference becomes an issue only in physics, where calories is a unit of measure for energy. As far as physics is concerned, we are expected to eat about 20,000 calories in a day. As far as the FDA is concerned, we're supposed to eat about 2,000 Calories a day.
Just wanted to clear that up.

Perhaps you should conctact the manufacturer of the machine. Anyhow, I think you meant 2300 calories, not 23,000.

Both numbers are well within expected error for that type of measurement. Bioimpedance isn't all that accurate a measure of body fat, as you've just discovered.

You're under 10%, and not an athlete, you really shouldn't be worrying about body fat very often, if at all.





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