Environmental Pollution Makes You Thicker or Never Forget Feedbacks in Data Analysis.

Recently I have come across this excellent article and decided to write a small follow-up.

The battle of Causality vs Correlation has been fought numerous times. Yet when analyzing how 2 correlating processes, A and B, affect each other, the first thing that immediately comes to one’s mind is most likely the simplistic “A causes B” or “B causes A”. What would be considered much less often, are feedback loops. Though not being common, they still present a major interest for a researcher.

In this note I will compare 2 phenomena from relatively different domains — obesity (public health issue) and accumulation of Persistent Organic Pollutants (environmental contamination issue) — and demonstrate how their inter-relation is far beyond what lies on the surface.

Obesity is defined as a condition having the body mass index (BMI) of 30 or more, which has now reached epidemic levels across the whole word. It is known that obesity brings a lot of negative health effects with it — from diabetes to cancer — and generally decreases the quality of life.

Persistent Organic Pollutants (POPs for short) — a name that a casual reader sees much less in everyday life — is a big group of pollutants, which all share a very low potential for degradation together with some chemical properties. The most substantial of the latter is lipophilicity — ability to attach and concentrate in fatty body tissues.

Furthermore, they can biomagnify — increase concentrations while moving up the food chain. The POPs (many of which are pesticides and fungicides) first make their way into grass. A cow eats this grass (well, lots of it) and becomes enriched with POPs. Then the cow gets eaten by you, dear reader, and POPs levels reach new heights in your body. Just like obesity, POPs may cause a variety of negative effects, ranging from infertility to cancer. Be calm though, numerous governmental authorities are watching food sold in shops day and night — so that doses of POPs in it are risk-free.

This, however, does not work with obesity, which is normally caused by a combination of genetics, overeating and lack of exercising. The more food of animal origin you eat, the more POPs are entering your body. The less you exercise, the higher is the potential of POPs to remain in your body. Thus, the extra kilos act as a catalyst for increase in health problems caused by both themselves and POPs.

Now, all the boring expositional stuff above is easily pooled from Wikipedia or a quick search on the internet. Does it make sense to dig deeper then? Certainly!

However, recent research suggests that POPs can actually directly cause obesity. The exact reasons are related to the change of human DNA under POPs burden, which significantly disturbs ability of a body to process carbohydrates. It is important to stress that POPs may enter human body not just with food, but also with water or atmospheric pollution. So even if you live on a diet consisted of exhaustively organic vegetables, you may still get POPs from pollution from elsewhere (e.g. from a nearby power plant), which will make you gain weight and amass more POPs.

Let’s summarize the information flow. Accumulation of fat leads to increase in POPs in a human body. In the same time, accumulation of POPs leads to increase in fat. Together they lead to similar health problems. Therefore, we may think of the flow as a positive loop inside a causality space.

So yes, though it sounds improbable, chemical pollution can make you make fatter. As for data analysis in general, it stresses the fact that we should never forget to exploit data domain knowledge to the fullest and remember that processes controlling this data may exist in complex loop-like patterns.