Genes R US — Diet, exercise and what genetic testing has to say about them
Posted: Wednesday, February 15, 2012 5:00 pm
I hate diets. I prefer to eat what I want, which by local standards is fairly healthy, minus my predilection for desserts. I also hate to exercise. Maybe that is because I am about as limber as a dried out twig.
I have found the most effective way for me to drop a size is to get sick for a couple of weeks. For example, this winter’s flu was good for five pounds. But counting on the serendipity (and discomfort) of illness is a poor diet plan.
The journal Nature reported this month that “there are now 30 percent more people in the world who are obese than who are undernourished.” The culprit is hypothesized to be a diet dominated by cheap, highly processed foods.
Given global trends (and my aversion to dieting and exercise), I was interested to learn what genetic testing had to say about my response to diet and exercise.
Numerous scientific studies over the last decade have found that our genetic make-up not only influences our food preferences, but also how our bodies metabolize what we consume. They have also found that the utility of exercise as (1) a weight loss tool and (2) for control of type-2 diabetes has a genetic component.
One simple type of genetic marker is the SNP (a single point difference in our DNA). Any SNP can only take on two values from the set: A, T, G, or C, where each letter is an abbreviation for a particular DNA base.
Each parent gives us one of our two values for a SNP. Thus for every SNP there are three possible combinations or genotypes. Ethnicity impacts the proportions of the population that fall into each genotype for a given SNP.
Consider SNP rs4994 that can only take on values A or G. Humans fall into one of three genotypes: AA, or AG, or GG for this SNP.
Asians have the smallest proportion of the AA genotype for rs4994, at about 67 percent. All other ethnicities have around 87 percent for the AA genotype.
In a 2003 Japanese study, fully one-third of the female Asian participants did not lose significant weight with simultaneous caloric reduction, walking and participation in a support group. The culprit was having an AG or GG genotype for rs4994. SNP rs4994 is found in a gene that controls how we burn our fat for energy and create heat in our bodies.
My mother, father, son, husband and I have the AA genotype for rs4994. If the Asian study is extensible to Caucasians, then dieting plus exercising plus support should work for weight loss for us.
One in 12 people are estimated by the Center for Disease Control to have diabetes (insulin resistance) in this country. Exercise is part of the overall recommendation to increase insulin sensitivity and control diabetes. Studies have found that two different SNPs impact the relationship between exercise and diabetes control.
In one study, SNP rs1800588 partitioned 450 Caucasian participants into three groups where exercise increased insulin sensitivity by 5 percent, 2 percent or not at all. My father, son and I fell into the 5 percent group; my mother fell into the 2 percent group. This SNP is part of the gene that encodes triglycerides and transports fat around the body.
A second study looked at glucose metabolism after 20 weeks of exercise. SNP rs1801282 split the 500 study participants of European descent into two groups. Those having at least one copy of a G in their genotype had greater improvement in glucose tolerance with regular exercise.
Not surprisingly, this SNP is found in a gene that is involved with fatty acid storage and glucose metabolism.
My father, mother and I are CG genotype for rs1801282. My son’s GG genotype is exceedingly rare, comprising less than two one-hundredths of 1 percent of the European population. The unfortunate CC genotype is most common — found in excess of 82 percent of the European population.
Here is where it even gets better for my family. This same SNP, rs1801282, implicates a larger waist circumference for the CG or GG genotypes if monounsaturated fat is omitted from their diet.
Saturated fats are the bad ones — for everyone. But for some people with genotype GG for SNP rs5082, consuming a diet high in saturated fats dramatically increases their risk of obesity. Thankfully, we do not have the GG genotype.
SNP rs5082 sits in the region that promotes cholesterol production. Caucasians have the highest prevalence for genotype GG at 20 percent. Asians are practically zero for the GG phenotype.
Lastly, genotypes AA and AG for SNP rs662799, found in a gene that regulates triglyceride levels, was found to be predictive of who can splurge on fat (more than 30 percent of their calories from fat) without gaining weight. Only my father has a lucky phenotype-genotype AG.
So what did I learn? Last week I learned that I have a genetic predisposition towards a thin to normal body type. This week I learned that I will gain weight if I eat all the high fat desserts that I desire. (Ok, cruising had already taught me that.)
Dieting and exercising with a friend should help me lose weight if I do eat too many desserts. My diet needs to include healthy fats, like olive oil, but no more than 30 percent of my total caloric intake. A “no” or “low” fat means an “apple” shape for me. Pass the olive oil, please.
Editor’s note: Nancy@ NancyMillerLatimer.com has worked in scientific research and development for 27 years. Published in The Messenger 2.15.12