DIY Electrical Body Fat Analyzer

Whether you are trying to drop some fat or build some muscle, it’s important to track progress. It’s easy enough to track your weight, but weight doesn’t tell the whole story. You might be burning fat but also building muscle, which can make it appear as though you aren’t losing weight at all. A more useful number is body fat percentage. Students from Cornell have developed their own version of an electrical body fat analyzer to help track body fat percentage.

Fat free body mass contains mostly water, whereas fat contains very little water. This means that if you were to pass an electrical current through a body, the overall bioelectrical impedance will vary depending on how much fat or water there is. This isn’t a perfect system, but it can give a rough approximation in a relatively easy way.

The students’ system places an electrode on one hand and another on the opposite foot. This provides the longest electrical path possible in the human body to allow for the most accurate measurement possible. An ATMega1284P is used to generate a 50kHz square wave signal. This signal is opto-isolated for user safety. Another stage of the circuit then uses this source signal to generate a 10ua current source at 50kHz. This is passed through a human body and fed back to the microcontroller for analysis.

The voltage reading is sent to a MATLAB script via serial. The user must also enter in their weight and age. The MATLAB script uses these numbers combined with the voltage reading to estimate the body fat percentage. In order to calibrate the system, the students measured the body fat of 12 of their peers using body fat calipers. They admit that their sample size is too small. All of the sample subjects are about 21 years old and have a similar body fat percentage. This means that their system is currently very accurate for people in this range, but likely less accurate for anyone else.

32 thoughts on “DIY Electrical Body Fat Analyzer

  1. Why is it society as a whole was WAY more fit pre-1970 and didn’t have a single gadget to track that “fitness”. Now in the 21st century, the States is fatter then ever, and every body and their brother has a fitness gadget. There is no miracle technical method of staying fit – it’s as simple as eat less, exercise more, and get off your couch and actually do things. You don’t need a gadget to tell you you’ve been on your ass for way too long, the seldom used mass between your ears should easily be able to monitor that status.

    1. There is a lot more high calorie processed or fast food available these days, while everyone uses their cars for everything and generally does as little as they can.

      It’s not hard to eat healthy and keep fit, people are just lazy and like too much unhealthy food.

    2. “eat less, exercise more”

      Except that’s not quite right either. The quality of foods is a large problem in todays age. When a single can of coke can and 2 coffees covers your 100% daily sugar intake it’s actually very hard to hit targets in the modern world.

      We live in the fast paced overworked world. We get up, go to work, grab a pre-packaged snack on the way. Work till lunchtime, go to the local fast food joint and have a small burger, work some more, head home absolutely exhausted and ready for bed.

      We mentally drain to the point where physical exercise is difficult. We eat crap to the point where eating less doesn’t make much of a difference.

      But if you do have that magic answer, now is the time to write a self help book and make some serious money.

          1. Yes, it is simple. Just not easy. I have to take my lunch to work every day, and to keep it healthy and financially doable takes a bit of work. I wind up eating a lot of salad, rice topped with just a bit of meat and sauce for flavoring, and some yogurt and fruit. I use stevia instead of sugar with my coffee, and try to avoid foods with high fructose corn syrup.

            Paying attention to your diet, getting regular exercise and rest, are habits that you have to develop over time. In my case it took several years and the motivation of my family medical history. A device like this really helps to throw your behavior in your face when you start slipping up and ordering lots of take out.

        1. Actually it’s not that simple. There is a growing body of evidence that obesity and weight gain is linked to changes in human gut bacterial populations. Gut bacteria have been found to modulate weight gain, as well as immunity and even stress responses. People who have had multiple antibiotic interventions since childhood have basically had most of their good gut bacteria absolutely decimated. There are various mice studies in which germ free mice have had their intestines humanized with gut bacteria from obese people. Thin mice with obese human microbiota gained phenomenal amounts of weight and became obese.

          Late last year, a clinical trial in the Netherlands used human gut bacteria from lean individuals to chage the compostion of gut flora in obese individuals. They lost masses of weight. Basically the problem is threefold: 1) overprescription of antibiotics which wreck the diversity of human gut bacteria and indiscriminantly decimate very necessary good intestinal bacteria which leads to weight gain 2) The difficulty of replacing key gut bacterial populations which have been lost due to antibiotic use (ie your average probiotic tablet does not contain key human gut bacteria which have been killed off by overuse of antibiotics, so once they’re gone, you’re screwed. Try finding a probiotic which contains Rosburia or Akkermensia – not possible). 3) The utter wasteland of nutrient-rich foods which help to keep gut bacterial populations steady and functional for human health. Most people eat to please themselves but coke, or cake or McDonalds doesn’t adequately feed intestinal bacteria.

          Then there have also been recent studies which suggest that gut bacteria can influence the kinds of food that you eat and that they are not just passive uncommunicative things living inside their hosts. (see: http://www.medicaldaily.com/gut-bacteria-control-our-minds-get-food-they-want-how-countering-can-fight-obesity-298394 )

          The other thing is that most babies born via viganal births have their mothers’ gut bacteria passed to them during birth. Babies born via C-section are more likely to develop obesity due to not having maternal gut bacteria transferred to them during birth. They get a bad start through no fault of their own. Babies born to mothers who have digestive diseases or obesity can also inherit the bacteria of their mothers and end up with the same digestive diseases or obesity.

          So, fat gain and loss is a much more complicated issue than just “stop eating junk food, and do some exercise”. You can change the composition of your gut bacteria to favour “good bacteria” in your gut by eating say inulin rich foods, but if you don’t have those good gut bacteria to begin with (for whatever reason), then you’re screwed.

          1. The other aspect to consider is that for several millions of years we have evolved under the conditions of scarce food and a very physical lifestyle. We are wired to seek out and consume as much high fat, high calorie food as possible, since the conditions for a very long time were that it may be a while before we encounter more. And our bodies are exceptionally efficient, since we needed whatever energy we had for flight, fight, foraging, and fucking – in short, for survival.

            Just 200 years ago, the conditions for most people was difficult enough that this conditioning still made sense. Even 100 years ago, conditions were tough for many. Just within the past ~60 – 70 years, food production has increased enough to reduce the average family’s food costs, while at the same time their annual income has increased. Even without McDonald’s and Coke, this combination means that the average family has the ability to buy a greater variety and a larger amount of foods than ever before. Along with that, the broad availability of transportation and the internet, reduction of manual labor, and increased population in cities have all contributed to a reduction in the need for our body to be as energy efficient as it is.

            Often, it is as simple as eat less, exercise more. But that doesn’t mean it’s easy… you’re fighting your survival instinct.

      1. It’s not just the low end at McD. Go to any mid range restaurant and the portion sizes are just ridiculous. It’s only at the ultra high end that the portions become digestible but who can afford eating at such a place regularly.

      2. If you stop HFCS (drinking soda for example) you will drop 10 lbs in 3 weeks. Thereafter you will continue to lose around 3 lbs every 2 weeks.

        I was curious about the research rhetoric suggesting ambiguity, and tested this on myself.
        No change to my diet other than removal of excess HFCS, and minimized refined sugars.

        I found that the lower sodium intake initially caused rapid water-weight loss, and then a fairly continuous loss of mass followed. This works, and note no other change to my diet or work routine was made.

        HFCS is a large failed experiment conducted on Gen X and Gen Y.

    1. Except that apparently nobody is concerned by the fact that this device violates the cardinal rule: you do not pass electrical current through the upper torso, for blindingly obvious reasons. They’re doing it. Intentionally! Ugh.

      It takes *very* little current to cause heart problems.

  2. The best way to do this is to directly measure your volume by submerging yourself in water and measuring your displacement (be sure to exhale as much air as you can first). From there you can calculate your density in g/ml and then derive your body fat percentage from either of the following formulas:

    Brozek formula: BF = (4.57/ρ − 4.142)
    Siri formula: BF = (4.95/ρ − 4.50)

    I tried this once, but unfortunately an inflatable pool and tape measure are not precise enough to give you a value better than approximately 1 g/ml, which is pretty much what you would expect from an ugly bag of mostly water.

      1. There are ways to keep oneself submerged (weights whose volume can be known) but, the floating/sinking issue is a body fat vs water density (so the salinity).
        I believe the tipping point in ‘typical’ water is around 15% body fat for neutrally buoyant – less than that (i.e. less fat) and you’ll sink, more fat and you’ll find floating easier but, if it’s very salty water then it makes the water denser so a lower body fat percentage will also float very easily.
        Now, as most people are not <15% fat, it stands to reason that most people do float but not everyone is (athletes can be anywhere down to around 7% and skinny people tend to be leaner)

    1. I was thinking of just that, glad there is someone who knows how to actually do it. Also couldn’t you use a larger container to measure the displacement? @Static. Tie a cinder block to the test subject, the displacement of the cinder block could be determined before hand and subtracted from the total displacement, and the upshot of this is the air will eventually be released from the subjects lungs so you’ll get a very accurate result.

      1. “…and the upshot of this is the air will eventually be released from the subjects lungs so you’ll get a very accurate result.”

        So, that’s what the mobs have been doing. I thought they’re getting rid of eyewitnesses while, in fact, they’ve just been taking their body fat measurements. (c:

  3. There is no such unit as “ua”! There is AU, however, it is next to impossible to express any amount of current with it. I may suspect you were thinking about microamperes, didn’t you? The you should have written “10 µA”.

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