Genes-R-Us — The gift of flab or the genetics of eating behavior

Genes-R-Us — The gift of flab or the genetics of eating behavior

Posted: Wednesday, February 8, 2012 5:00 pm

I live in the Mid-South. The latest genetic news on eating behavior and measures of obesity may be unpopular and perceived as downright rude topics in this part of the country. 
But, hey, perhaps I have good news for you. Maybe it is just easier for some people to keep that slim, trim look, as you have always suspected. Maybe it isn’t eating all that deep-fried bologna or deep-fried Twinkies, after all. Maybe it really is Mom and Dad’s fault.
No matter what the genetic studies have to say, in my first two years here I have gained 10 pounds. Assuredly, my DNA did not change when I left San Diego for the excellent weather of Union City. But my eating and exercise habits sure did — temporarily so, ahem. 
Let’s start with the concept of disinhibition. That sounds scientific but it simply means: lack self-control over food consumption. If you struggle with disinhibition, then you are more inclined to continue eating even though your stomach is full — you may still feel hungry or not quite satisfied.  
Disinhibition has been associated with those single point differences in our DNA, called SNPs. One such SNP is rs1726866 in the TAS2R38 gene; and we humans can only have A’s or G’s in that position. Dad and Mom each make a contribution. I am GG, as are my parents. My husband is AG.
In a small study of 381 Amish women, those with the rs1726866, GG genotype, were best able to control their eating. Those with AG genotype were typical in their overeating eating patterns. But those with the AA genotype were far more likely to overeat. 
Having an A for the rs1726866 SNP allows one to taste bitterness in food but it also seems to be involved with sensing our stomach contents.  Interestingly, this SNP is not associated with Body Mass Index or BMI. Let’s look at those SNPs next.
The higher the BMI, the more weight one carries relative to their frame. Here are some benchmark values that provide a feel for the spread and interpretation of values:
Weight State: BMI
• Starvation: < 15
• Underweight: < 18.5
• Normal weight: 18.5 –  24.9
• Overweight: 25 – 29.9
• Obesity: 30 – 40
• Morbidly obese: 40 >
For an adult, a half a BMI unit equals two to six pounds, depending on gender and age. Since I started calculating my BMI, some 18 years ago, I have ranged from underweight to normal.
23andme reports on nine SNPs that are associated with lower, typical, or higher BMI. Seven out of my nine results are associated with a lower BMI and the other two are typical. Altogether, this could account for an estimated 10-15 pounds toward a lower weight. Nothing to sneeze at.
My son, father and mother have similar results for the nine markers; my husband’s markers are pretty much typical. Note that this is independent of eating habits and exercise. There are separate SNPs for those. 
There is an awesome animation (select play) at www.cdc.gov/obesity/data/trends.HTML that shows how BMIs have changed between 1985 and 2010. The U.S. map shows the increase in state-averaged BMI values as the colors of individual states change from light blue to dark red over 25 years. 
The increase in our country’s BMIs is wholly mind-boggling. What fundamental change occurred in 25 years to impact our bodies is such a humongous way? 
In my opinion, there has been a change in the way we eat and play as a country, i.e., our diet and level of activity. But that is the topic of next week’s column: genetic markers of response to diet and exercise. 
On Jan. 31, the Wall Street Journal reported that the “average daily media use by girls ages 8 to 12 in recent Stanford University study was 6.9 hours.” I doubt that it is any less for boys. 
Although the study was focused on the negative impact of this extreme media use (like texting) on the girls’ social skills, given what we now know about the impact of exercise on gene expression, I am glad that I was born in the ’50s — and not the ’90s. 
Given what we now know about epigenetics, transferring gene expression patterns across generations, I am glad that my parents were NOT born in the ’90s, too!
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Editor’s note: Nancy Miller Latimer has worked in scientific research and development for 27 years. Published in The Messenger 2.8.12

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