Nature vs. Nurture: Is Your Body a Slave to Your DNA?

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By Julie Chen, M.D.

Since intelligent thought first came into existence, luminaries like John Locke, Shakespeare, and Darwin have debated the influence of our environmental factors over our innate, genetic factors. The simple question of nature vs. nurture, however, is too simplistic, and while scientists and doctors understand that the two are in fact deeply interwoven, we are just on the brink of discovering how much our DNA affects our health as well as how much our lifestyle affects our DNA.

Obesity In Twins

In 2009, a study came out in the American Journal of Clinical Nutrition that had the fortunate opportunity of studying 1,034 complete pairs of twins from Denmark and Finland (1). The objective of the study was to examine the genetic variation of body mass index (BMI), waist circumference, and percentage body fat in relation to physical activity and protein intake.

A study like this has huge implications. This study suggests that what we eat and what we do, as in level of physical activity, can help us determine how our health is, instead of just from our genetics. In support of this, the Human Genome Project had just been completed a few years prior to the study (2), and the phrases, “Oh, it’s just genetics,” and “It runs in the family,” were ubiquitous (and still are).

The Role of High Protein Diets & Physical Activity

The results of the study confirmed previous findings and the researchers were able to conclude that physical activity and diet do have a noticeable and significant effect on your weight, despite your genetic predisposition. In this specific study, they found that a high level of physical activity was linked with lower mean values, while a high proportion of protein in diet was linked with a higher mean BMI, waist circumference, and percentage body fat; however, this finding only applied to Danish men and not in women or Finnish men. While the impact of a protein-rich diet on weight is still uncertain based on this study, the effect of exercise on weight is clear. Using complete pairs of twins, we were able to have a better understanding of the role that physical activity has in reducing weight and percentage body fat. Further studies on protein and how that affects the expression of obesity gene still needs to be done.

Turning Off Your Genes

With regards to genetics, things get a little more interesting in this study. High physical activity was found to be associated with a significant reduction in genetic variation. What this means is that there is evidence that strongly suggests high levels of physical activity can modify the expression of the genes responsible for predisposition to obesity. This further supports a previous study that found an increase in BMI due to the rs9939609 polymorphism of the FTO gene in sedentary persons, but not in physically active individuals (3). The excuse, “It’s genetic,” may no longer apply to our health, at least with regards to our weight and waist circumference.

And in the case of protein intake, the study found that “the protein content of the diet has no appreciable effect.” Now this is still up for debate, and indeed the study recognizes that reporting bias may be at play here. According to the researchers and a previous study (4), obese individuals are more likely to underreport their total caloric intake, but to a lesser extent their protein intake. Because of this reporting bias, the actual proportion of protein may be much lower than what is reported in obese persons. Further research and study therefore needs to be conducted before we can say with confidence what influence protein has on our health and genetic variation.

Know Thyself

Since 2009, there have been myriad studies that support the theory that lifestyle and diet have an affect on one’s genetics and health (5)(6). What we’re starting to see is an understanding of how our genes are expressed and the control individuals have over them through lifestyle and diet choices. As with many other aspects of our lives, it’s important that in the realm of health each individual practice the ancient Greek aphorism: know thyself. If you know that you have a family history or genetic predisposition to obesity, heart disease, or other conditions, you have a choice (to a certain degree) in how that gene is expressed. And while you may be genetically inclined towards certain medical conditions or physical traits, your choices in lifestyle and diet can influence your risk of developing those attributes.

As technology becomes more accessible, it’s become easier for individuals to attain in-depth DNA reports in addition to their family history. Knowledge is power, and understanding both your genetic make-up and lifestyle is the key.

Sources:

1. Silventoinen K, Hasselbach AL, Lallukka T, et al. Modification effects of physical activity and protein intake on heritability of body size and composition. Am J Clin Nutr. 2009;90:1096-103.
2. “All About The Human Genome Project (HGP).” National Human Genome Research Institute. National Institutes of Health, n.d. Web. 29 Oct. 2014. .
3. Andreasen CH, Stender-Petersen KL, Mogensen MS, et al. Low physical activity accentuates the effect of the FTO rs9939609 polymorphism on body fat accumulation. Diabetes 2008;57:95-101.
4. Heitmann BL, Lissner L. Dietary underreporting by obese individuals-is it specific or non-specific? BMJ 1995;311:986-9.
5. Qi Q, Chu AY, Kang JH, et al. Sugar-sweetened beverages and genetic risk of obesity. N Engl J Med. 2012 Oct 11;367(15):1387-96.
6. Jääskeläinen T, Paananen J, Lindström J, et al. Genetic predisposition to obesity and lifestyle factors – the combined analyses of twenty-six known BMI and fourteen known waist:hip ratio (WHR)-associated variants in the Finnish Diabetes Prevention Study. Br J Nutr. 2013 Nov;110(10):1856-65.

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