Is DNA Destiny?

Author: S. Bledsoe, M.D.

You wouldn’t really expect a SWAT member, ex-miltary, workout guru, diet-crazed, genetic freak to need a quadruple heart bypass at the ripe age of 39.  As it turns out, my friend was a genetic freak in another sense.  Virtually everybody in his family died of heart disease at an early age.  His strong family history for heart disease caught up with him before the age of 40.  He did his part, but he couldn’t fight genetics.


Some debates will never be totally settled.  Which College Football Conference is the best?  Was there a shooter on the grassy knoll?  Who is D.B. Cooper?  Is “nature or nurture” predominant in determining physical traits?  While I won’t presume to solve the assassination of JFK in the next few paragraphs, science does have something to say about the “nature vs. nurture” debate.  They are interdependent, tightly dove-tailed parameters that play an integral part in the development of our physical and behavioral traits.  As it relates to obesity though, it would appear that “nature” has a lot to say on the matter.

Twin studies conclude that genetics plays a significant role in obesity.  Some of the most fascinating studies are those done on identical twins who were raised in separate households.  If environment is key, these twins should have very different rates of obesity.  If genetics is the stronger influence, they will have similar rates of obesity in spite of different environments.  The New England Journal of Medicine published an article in 1990 that analyzed 93 sets of identical twins reared apart, 154 sets of twins reared together, 218 sets of fraternal twins raised apart, and 208 sets of fraternal twins raised apart.  This large study concluded that “genetic influences on body-mass index are substantial, whereas the childhood environment has little or no influence.”


Studies of adopted children also conclude that your chromosomes play a huge role in obesity.  Another study from the New England Journal of Medicine examined 540 adoptees, analyzed their weight classes then compared them to their biologic and adoptive parents.  Amazingly, the adopted children were much more similar in body structure to their biologic parents than to their adoptive parents.  So striking support for this that the researchers concluded that “genetic influences have an important role in determining human fatness in adults, whereas the family environment alone has no apparent effect.”


Recent genomic and epidemiologic studies conclude that, you guessed it, at least some of obesity is, unquestionably, inheritable. According to a 2007 study that analyzed the data contained in recent efforts in genetic mapping and then harmonized this with current genetic epidemiologic research, somewhere between 6-85% of obesity is inheritable.  That is a wide range to be sure, but the researchers felt that this was a reflection of the differences of inheritability for different populations.  Suffice it to say, genetics plays a more than casual role in obesity.


If you are getting a shiver down your spine because your family genetics resembles Sherman Klump’s from The Nutty Professor, remember that DNA is not necessarily destiny.  There is a saying in genetics- there are many phenotypes for every genotype.  In other words, your chromosomes determine a preset range but your environment and decisions pinpoint your landing spot for your observable characteristics.  A classic example is height.  I am 6’2” tall.  My genes say I will never be a Shaquille O’Neal nor Spud Webb.  My God given height range may have been from 5’8” to 6’3”.  My healthy upbringing, good nutrition, and safe environment dictated that I was able to nearly reach my full genetic potential.  My choices, and the choices of those around me, had a positive influence on my genetics.


Obesity is the same way.  You may never be confused with Arnold Schwarzenegger, but you can reach your full genetic potential with hard work and discipline.  Or you can always get more deconditioned by sitting on the couch eating Cheetos.  Where in your preset genetic range you choose to land is up to you.

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