Can a genetic test tell if youâ€™re going to become fat?
Simple observation suggests overweight and obesity tend to run in families, and indeed the search for genes that affect the tendency to pack on pounds has found a growing list of genes that each contribute to overall risk. The most famous of these genes is the FTO gene on chromosome 16 – the presence of specific “risky” versions of this gene is correlated with an extra 3 pounds for each risk-increasing copy (we have 2 copies of each gene).
But overweight and obesity are clearly influenced only partly by genetics and we can also explain the tendency for familial overweight by the fact that families often share eating and activity habits.
It’s also clear that during the past three decades, while obesity rates have tripled, the genetic makeup of the population has not changed dramatically. Therefore environmental factors (food intake and activity levels) are clearly responsible for this rapid rise in obesity. The genetic makeup can only take responsibility for making some people more susceptible to these environmental factors.
Genetic testing of obesity
I love the field of human genetics: It uses math, biochemistry, probability and family stories to slowly reveal deep mysteries about who we are. Studying our genetic makeup also holds enormous medical promise.
Is genetic testing ripe for primetime? Most people in the field are humbled by the pace of discovery in genetics, and have a feeling we know less than we think we do. Nevertheless, the growing interest in genetic assessment has already sprouted commercial companies that offer genetic testing directly to consumers. The future is apparently already here, and these companies suggest not only that they can calculate your risk, but also that knowledge will empower better health decisions.
Since obesity is a really important contributor to disease, one of the risks these companies assess is one’s personal likelihood of developing obesity. A company called deCODEme tests 11 variants in 11 regions of the genome known to increase an individual’s risk of being obese; 23andMe offers an obesity risk assessment based of 2 genes; all you need to do is spit into a tube (and part with a bit of money). The results of these genetic screens are given as lifetime risk and relative risk compared to the average person.
Genetically discovering yourself – and then what?
Let’s say we’ve reached the point at which we can really tell who’s at greater risk for obesity, is this data worth knowing? Would recognizing you’re at risk lead to risk reduction through a better diet, or rather to hopelessness and fatalism?
A new study in the journal Obesity examined the reactions to theoretical results of genetic testing for obesity risk in two groups of British respondents: 306 overweight and obese students, and 395 normal weight students. The participants received a result that either told them their risk is average or that it’s above average.
In both groups, telling the individual that they were at higher risk for obesity led those people to anticipate they’d be more motivated to adopt a healthier lifestyle. Again, this is a theoretical study, as no real genetic testing was done. The study concludes that genetic testing “may offer an opportunity for behavior change if the feeling of “at-risk” can be linked to action by providing concrete information weight gain in conjunction with the test.”
We’re all at high risk
Even without personal genetic testing, I think most of us can estimate whether our risk for developing obesity is at or above par. A quick survey of the genetic pool during family reunions, an honest look at one’s eating habits and at personal weight trend over time are quite informative.
Perhaps genetic testing can make the assessment just a tad more informed, but does it really make sense to assign risk for a condition that is so very common? Or does the knowledge, that in all western countries the majority of people develop overweight and obesity tell us all we need to know?
The best-case scenario – the result of “you’re at average risk for obesity” – predicts that there’s a pretty reasonable chance you might become obese. The last few decades have proven that we all have a tendency to overeat when food is plentiful, tempting and calorically dense, we all tend to store the extras – a tendency that served our ancestors very well – and given the chance, we prefer watching TV to chopping wood.
And if knowing we’re at-risk may offer an opportunity for behavior change let’s announce it right now: We’re all at risk for obesity, each and every one of us, some even more than others. So let’s all do something about it.