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Old 06-24-2007, 07:57 PM   #1
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Join Date: Sep 1999
Posts: 9,160

Default Topic 5 - Genetics And Weight

I must start off with my favorite quote in the entire book:

Currently, lean people think they stay lean because they are morally superior Ö (research) says it is because they are genetically lucky. (p 180)
Love it! I immediately think of several smug and disdainful people in whose faces Iíd like to wave that quote. So, keeping them in mind, letís discuss the genetics of weight.

Itís common knowledge that obesity runs in families. But thereís debate over the reasons why Ė is it nature or nurture? Biology or environment? Or a combination of the two?

Rethinking Thin comes down firmly on the side of weight being determined by genetics:

Ö People have only a limited control over the amount they eat and what they weigh. Ö Body weight is genetically determined, as tightly regulated as height. Free will, when it comes to eating, is an illusion. (p 142)
Chapter 5 reviews several well-known studies of adoptees and identical twins raised separately to conclude that a tendency toward a certain weight is more strongly inherited than many other physical traits, including tendencies toward mental illness, heart disease, and certain cancers.

It takes the position that weíre all born with genetically determined weight ranges of perhaps 20 Ė 30 pounds and within that range, itís not difficult to manipulate weight up and down. But, the theory is that itís extremely difficult to take the body outside of itís comfort zone, whether above it or below it. The body will fight hard to return to its set point or comfort zone.

To me, the science linking weight to genetics is compelling. But what the book glosses over is that weíre talking about genetic tendencies here. And a genetic tendency has to be nurtured in the right environment in order to be expressed.

When my son was diagnosed with diabetes at age 17, we were shocked because we were told that diabetes is a genetic disease -- but there was no diabetes on either side of the family. Ah, the doctors said, there has to be an environmental trigger in order for the diabetes gene to be expressed. Itís a genetic tendency with an environmental trigger. So the gene may have been there for generations but never triggered.

I kept thinking about that as I read about weight and genetics. Weight being determined by pure genetics can't be the end of the story, can it?

Take height, for instance. The average American today is three inches taller than during the Civil War (from the book). Genetics havenít changed in that time; the environment changed with better nutrition and less disease. In today's environment, that same height gene is fully capable of being expressed.

Likewise, even if weight is as tightly controlled by genetics as the book argues, it still needs the appropriate environment in order to be expressed. A gene for obesity is going to find a pretty hostile environment in rural Africa, but in the United States today, conditions are such that it can flourish and be fully expressed.

In light of the book's agenda, it's not surprising that it doesnít deal with the question of why Ė if weight is indeed genetically controlled Ė have the levels of obesity risen so dramatically in the past three decades? Certainly we havenít had enough time for our genes to have mutated, so what did change? Could it be -- the environment?

What do you think about the studies cited in the book? What are your thoughts on weight and genetics? Are we absolving ourselves of responsibility if we believe that our weight is genetically determined? Or can the awareness that we may have the genetic cards stacked against us make us more careful and vigilant about our environment?

Is the book conveniently overlooking the role that environment plays in the expression of genes? If environment is the trigger for obesity genes, what are the implications for the world weíre raising our children in today?

How about your family? Is it an obese or overweight one? What about the environment you were raised in? What do your personal experiences tell you about genetics and weight?

Please share your thoughts and reactions.
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