3 methods of measuring body fat compared over 100 days

Way back – about 9 years ago I went on a 3 month challenge (100 days to be precise)  The aim of the challenge was to lose fat and build muscle – very similar to “Body For Life”. It was a local New Zealand challenge run by supplement company Miada – they  supply supplements to, and train body builders. (Such a great way to get people to buy your product!)

I worked out at the gym 4 – 5 x week, a body builder type programme – weights and cardio. The diet was designed for body builders; 50% calories from protein, 30% from carbohydrates and 20% from fat.

Anyway – I did a little N=1 study during the 14 weeks measuring my body fat in 3 different ways. I wanted to see:

1. Do the 3 methods come up with the same body fat calculation?

2. Do they show a comparable amount of change of body fat over the 3 months?

3. If there were discrepancies – what would explain these?

The three methods of measuring body fat were:

1. Bioelectrical impedance analysis (BIA) I have a set of Tanita stand on scales. This method uses an electrical current which runs up one leg, through the lower abdomen / pelvis and down the other. Despite a general public percep­tion that BIA measures “body fat,” what is actually measured is the electrical impedance of body tissues, which provides an estimate of total body water (TBW). Using the measure of TBW derived from BIA, the body fat is estimated.

2. Skin folds measurements and calculation of body fat

Body fat is measured by calipers and was done by an experienced personal trainer at 4 sites – Subscapular, tricep, bicep, suprailliac

3. Zone body fat calculator- which is based on measurements. Hips at the largest point, waist at the navel. The ratio of these two measurements to height gives a fat percentage estimate. This calculation can be found in the back of ‘Enter the Zone’. Or this one on the Zone diet site.  It is similar to the US Navy circumference method

I also tracked my Body Mass Index and body weight (in kilos – multiply by 2.2 to get pounds) to see how it compared to fat loss.

So – for the sake of science – I’ll let you all know some intimate details of my body size, weight, shape and fat percentage!

Here is a weekly chart with all the measures:

And here are before and after photos (cringe!) so you can see what the actual body fat changes looked like.

So how did the 3 different body fat measurements compare?

Skin Fold: This is measured on the part of my body with the highest amount of fat, so for me this method worked out at the highest body fat percentage.  Each person has a different distribution of body fat. I tend to carry more on my trunk and the back of my arms (tricep). When I put on weight – I’m more apple than pear. These 4 caliper sites are where the majority of my fat is situated. Therefore it tends to measure mine on the higher side compared to other methods. A pear shaped woman on the other hand with more body fat on the hips and thighs, and less on the trunk would measure considerably less than me using this method – even if she had a total body fat exactly the same as me.

Zone Calculator: worked out at a lower body fat estimate than calipers. Why? Because of the measurements used – bottom at biggest part and waist at navel. My butt is pretty small, I don’t carry much fat on my hips and thighs. This method may underestimate my body fat a little.

BIA: This method consistently measures my body fat lower than other methods. As it  sends a current up one leg and down the other, it only measures electrical impedance in the lower half of the body. I carry less fat here, therefore it gives me the lowest body fat estimate. If this method included body fat at the top half of me – it measures about 3% higher.

Change over 3 months: Both the Zone calculator, and the skin fold methods tracked body fat down in a very similar way, and showed almost the same change. BIA on the other hand jumped all over the place.

BIA – why so much variation? BIA sends a small electrical current and measures the amount of impedance to this current. Some tissue impedes the current more than other tissue.  Fat has less water in it than muscle, and so it impedes the current more. The more impedance the higher your body fat will be measured.

A number of factors increase impedance:

Less fluid in tissues. This is affected by factors such as dehydration, blood flow to lower limbs / dilation of blood vessels. Exercise and a hot environment will increase blood flow / dilation, decreasing impedance and giving a lower body fat measurement. Cold environment, dehydration, no recent exercise will mean less blood flow / constricted vessels – measured as more impedance and a therefore a higher body fat. Hormonal changes affect fluid retention. As most of us girls know, we can retain fluid prior to our menstrual cycle. More fluid, less impedance, measured as a lower body fat.

If you look at the last 2 measurements – you’ll notice something interesting. Body weight change 50.4 to 49.3 – a kilo. Yet body fat by BIA 18.4 to 18.1, only a slight change. Why? Well the last week or so of this plan involved a low calorie diet, no salt and a herbal diuretic. This was to get the leanest look possible for the photo. So yes – body weight dropped, but because I was dehydrated in comparison to the previous measurement, the body fat measured higher than it otherwise would have. (I estimate 0.5 – 0.8 was fluid loss)

Okay – so what do I think about all this? What method do I think is the most accurate?

Calipers / skin fold – only if measured by a skilled person, and using the same person to follow through. I’ve had skin fold measurements vary about 6 %, just by having another person do it.

Zone calculator: Measurements – hip / waist compared to height, for me this is an accurate self measure. My navel measurement is the quickest to respond to diet / stress / food quality. However for some the waist is easily effected by bloating or fluid retention.

As for BIA – this is only accurate if all these factors are in place:

• It must be done at the same time every day – best time according to the information provided is late afternoon, before dinner, lunch is well digested and you are well hydrated.
• Same level of hydration, nothing affecting a change e.g. – salt intake, alcohol, fluid intake, time of month for women.
• Same amount of exercise
• Same environmental temperature

Despite this – I like the BIA scales, because they are fun.  My new ones – Tanita Innerscan have a big range of measurements including: total body fat, hydration, visceral fat (that’s the internal bad stuff), bone weight, muscle weight and body type, and taking all these into account – it will give you your metabolic age. If you are strong and lean, and have low visceral fat it is very complimentary. No other method will show you your visceral fat.

What about using BIA to track clients’ body fat?

I am aware many health professionals use BIA to track clients’ body fat, but in my opinion they are not accurate enough to track body fat. In the above experiment, I used the scales at exactly the same time of day and tried my best to have no change in variables – but they still showed a  lot of variation in measurements. For this reason I don’t think they are a suitable way to track a client’s body fat changes. By far the easiest – and in my experience, accurate enough for the average person are measurements and scale weight. They can be useful though to give clients immediate feedback as to fat percentage and especially visceral fat. This allows people to look at body fat and not just weight on scales, which gives no indication of bidy fat.