Does a body composition scale provide independent information? Two experiments: weight and age

Since the beginning of the year I have gained about 8 kg. Was that fat, muscle, water? Probably some of all. My body fat scale estimates that my body fat percentage has increased by about 3%, which would be 2 to 3 kg of fat.

The problem

My problem? My scale knows my weight gain and likely uses my weight to estimate my body fat percentage. If it would not use my weight to estimate body fat, why would it want to know my height (body mass index, BMI), age and sex? Part of the information on body fat likely comes from the currents send through my body by the scale, but another part from my weight or BMI. Thus my problem is, does the increase in body fat percentage tell me more than what I already knew, that I have gained 8 kg?

The experiment

Now luckily, my fitness studio has another instrument to measure body fat. It is attached to a computer and also wants to know my weight. But here, you have to type in. Thus with this instrument you can experiment.

The instrument has a infra-red sensor that has to be placed on your biceps. To compute your body fat, and a colorful page full of other probably highly reliable information, it uses your weight, height, age and fitness.

We made one measurement stating my real current weight and one stating my weight at the beginning of the year. The difference in computed body fat percentage: 3,3%! Almost to similar to the increase estimated by my scale to be true.

The interpretation

It is possible, I gained some fat and my waist did increase some. It is also possible that nothing happened fatwise, other places look more muscular nowadays. I guess all I know is that I gained 8 kg.

I guess this does not surprise scientists and engineers working on these measurement devises. The German Wikipedia even mentions this effect qualitatively. But I am not sure if all users are aware of this problem and we can now put a number on it. If your fat gain is less than a third of your weight gain, the measurement is too uncertain to determine whether there really was a fat gain.

Post Scriptum. We forgot one experiment. I would love to know what the estimate for my body fat percentage would be if I tell the computer I am a young man. I expect some age discrimination by the multiple linear regression equations used.

Post Post Scriptum. Thanks to Caro of Stangenliebe (Pole art fitness Bonn) for the measurement.

UPDATE. I realised I could do the experiment with my age using my own scale. My Soehnle scale has two presets. I set person 1 to my age (rounded to 42) and person 2 to an Adonis of 18 years. In all four measurements the Adonis has exactly 3.7% fat less. If only my age group would not be so overweight, my readings would be a lot better.

The social dimension of health

Maybe I could even have title this post: the social dimension of life.

Many people seem to interpret "survival of the fittest" as relating to the fitness studio. While the fittest are simply those who survived. Whether you survive depends on lot on your tribe and only partially on your self, if you do not behave too stupidly.

Frank Forencich speaking at the Ancestral Health Symposium, 2012, explains this social part of health and a full life.


Frank Forencich is blogging at The Exuberant Animal and is a refreshing sound in the paleo world. His posts are thought provoking and well worth reading.

Paleo and fruitarian lifestyles have a lot in common

My new fitness trainer eats a lot of fruit. And she looks darn healthy. Now I know, you should not take weight-training advice from a professional body builder or risk serious overtraining, but still I was intrigued and did some research. The vegan and paleo communities are often not on friendly terms. Thus what struck me most researching fruitarian blogs, was how similar many of the ideas were.

A very strict fruitarian only eats fruits in the common meaning, sweet and juicy fruits from trees or bushes. Others also include vegetable fruits such as avocados, tomatoes and cucumbers, still others also include nuts, many regularly eat salad. To get sufficient calories from fruits, a fruitarian has to eat several kilograms of fruit. Some people calling themselves fruitarians actually get most calories from nuts and avocados. In this post fruitarians are people getting most calories from simple carbohydrates, that is from sweet fruits.

The paleolithic lifestyle is inspired by the way people lived before agriculture. As the information from the Paleolithic Age is scarce, in praxis this often means, that existing hunter gatherers and their diets and lifestyles are studied. Such bands often trade with nearby agriculturalists and thus no longer live a true stone-age life. Still as long as they are free from the deceases of civilisation, they provide good role models in my view. Similarly, many paleos also look at other existing cultures that are in good health. In this respect the paleo community is close to the Weston A Price Foundation, who seek guidance with how people lived a few generations ago. The paleo diet is best defined by what it not eaten: processed foods, grains, sugar and refined seed oils.

Is obesity bias evolutionary?

On the Huffington Post and on his own blog, David Katz, MD, asks the important question why so many people are obese nowadays. His answer does not sound convincing, he argues that there a bias toward obesity is an evolutionary advantage.

This might have been possible, but a simple calculation shows that this is unlikely. A man who is 100 kg too heavy and 50 years old, to a first approximation ate 2 kg per year too much. Two kilograms of fat is 1400 Cal and thus comparable to what one eats in 4 days to one week, depending on your, height, weight and level of activity. In other words, this man ate only about one or two percent more than he should have. You may increase this number somewhat to account for the fact that a larger body also needs more energy. Still the additional amount eaten by an overweight person is small and will be hardly noticeable in day life.

In the times that humans were hunters and gatherers, it should have been easily possible to eat a few percent more than usual. The year to year variability in the availability of resources is large; on the negative side think for instance of floods, droughts and grasshopper plagues. A human that is able to survive in a bad year, should easily be able to hunt or gather double his need in good years. One would expect the maximum amount of food a person can find is much more than a few percent more than the average needed. Otherwise, a human with a bit of bad luck would soon starve to death and be removed from the gene pool.