Nutrigenomics and Genetic Testing: can you out run your genes?

By Kaitlin Isbell

The Nature Versus Nurture debate is a tail as old as time. This debate will likely continue to waver on, but in all reality both philosophies hold some weight and the truth is more of a spectrum than a definitive answer. 

Most people would agree that a baby resembles his or her parents in physical appearance at birth. As the child matures they will likely start to take on personality traits and mannerisms learned from their environment. When it comes to genes, it’s sweet that you have your mother’s nose or attribute your great hair to your father’s side of the family, but it’s astonishing how the energy in the room changes when the conversation shifts from comparing eyes and lips to discussing the families’ generational history with cardiovascular disease.  Are you destined to walk the same path? And if you knew you were genetically predisposed to cardiovascular disease or other conditions such as diabetes or cancer, would you accept your fate or fight as hard as you can to live a healthy lifestyle and try to outrun your genetics? Or would you prefer to decline genetic testing and deal with the trials as they come?  

Genetic verse environment:  

Research shows that both genetics and environment play a role in pathogenesis. The specific condition ultimately determines the extent to which genetic or environmental factors play a role. For example, in single-gene disorders like Huntington’s disease, genetic factors outweigh environmental factors. Twin studies working with obesity showed that 80% of the difference observed in BMI between the twins was related to genetic factors1.  Type 2 diabetes has a multifactorial pathogenesis, we know that environmental factors such as weight, physical inactivity, and dietary intake lead to insulin resistance, but there have also been 65 SNP’s associated with developing the disease1. The AHA identified that among environmental factors diet may be the most directly involved in the genetic modulation of the different phenotypes of cardiovascular disease. Dietary factors might modulate the risk imposed by genetic susceptibility due to variation in one or more genes involved in the etiology of cardiovascular disease3. A twin study on genetic and environmental influences on serum lipid levels concluded that genetic factors on serum lipids tend to decrease with age and early environment appears to be an important factor in total cholesterol later in life4. 

Genetic Testing:

Since genetics and environment both play a role disease development, it is important to have a way to test for genetic factors. As technology advances, genetic testing has become more readily available and is more accurate than ever before. Genetic testing continues to grow in popularity and allows people to track their ancestry back to upward of 1000 years.  Beyond tracing family lineage, scientists use predictive genetic testing as part of newborn screenings for single-gene disorders such as phenylketonuria. When it comes to single-gene disorders that will lead to a definitive diagnosis and currently have no cure, like Huntington’s disease, genetic testing is only done at the patient’s request. Predictive tests can be used to identify mutated genes that could trigger a disease. For example, women who carry certain BRCA1 and BRCA2 mutations have a 60-80% risk of developing breast cancer1.  Predictive genetic testing can also be done to identify gene mutations in diseases like ovarian cancer, colon cancer, childhood polyposis, childhood sarcomas, Alzheimer disease, lung cancer, and polycystic kidney disease. The figure below shows the specific gene mutations associated with each of the conditions. 

After a person undergoes genetic testing and is found to be at a higher risk for a condition, what other factors have to be present that will ultimately lead to the development of the disease? Environmental factors like cigarette smoking, physical inactivity, prolonged periods of stress, and diet are all modifiable risk factors that when unmanaged put a person at a higher risk for disease development. 

What is Nutrigenomics? 

The field of Nutrigenomics is that was created to assess the interaction between genes and nutrients. Nutrigenomics is the area of nutrition that seeks to understand how the components of a particular diet may affect the expression of genes, and seeks to identify weather the diet increased or suppressed gene expression. An individual’s nutritional state is the result of an intervention between various factors, such as genetic background, physical body, emotional needs and social state. Diet is a key factor, since the nutrients and other bioactive compounds in food can be beneficial or initiate several diseases. The conditions most closely related to food consumption include: celiac disease, phenylketonuria, and non-transmissible chronic diseases such as cancer, diabetes, and dyslipidemia2. 

Using Nutrigenomics to our advantage :

Nutrigenomics is a way of working with nutrition and the knowledge of how food interferes with the genetic code and how the body responds to these interferences and with the phenotype2. Unfortunately, individuals do not have the option to choose their genetics, but in many conditions certain lifestyle interventions can help to avoid pathogenesis or delay the progression. Research in Nutrigenomics has helped to identify ways in which the bioactive compounds in food can be used to combat things like a genetic predisposition. For instance, the chronic inflammation found in obesity can be decreased through the use of bioactive compounds such as tyrosol found in olive oil or lycopene found in tomatoes, guava, and watermelon, these bioactives work to decreased inflammation by inhibiting the expression of genes and co-factors associated with the inflammatory process. Micronutrient deficiencies have a narrow link to the development of cancer. Deficiencies in folic acid, selenium, niacin, zinc, vitamin B12, vitamin B6, vitamin C, and vitamin E can lead to changes in DNA and can lead to rupture of the double strand of DNA, oxidative lesions or both. Although the link between micronutrient deficiencies and cancer development is relatively small, it is important to take into account especially if an individual already had one of the gene mutations associated with cancer pathogenesis. Additionally, most of these micronutrient deficiencies could be solved through a healthy diet with a focus on increased fruit and vegetable consumption.

Personalized Nutrition

Currently, dietary guidelines are based on what proves to be the most beneficial for general population. Dietitian’s use these guidelines and tailor them to the individual client. Individualized practice is preferred since we recognize that everyone is different, therefore so are their nutritional needs. The idea of personalized nutrition essentially takes individualized practice a step further by also applying genetic components. Personalized nutrition is still in infancy stages and will need more research on practicality, feasibility and consumer acceptance5. 

Psychological aspects and implications of Genetic testing 

As research continues and more genetic insights become available, it is essential that all testing is done with the clients wishes and best interest in mind. Genetic testing is great in the sense that we can uncover potential risk factors and make lifestyle adjustments accordingly, but it is understandable that some people would rather not know this information. Special considerations for counseling on what results mean and what implications result from them should be given. 

One of the most popular forms of genetic testing is through the mail or digitally, the results are given to the individual and it is up to the individual if they choose to seek professional guidance on the implications of the results. The results include things like ancestry data, but can also include nutrition information such as susceptibility to nutrition related diseases, potential risk for nutrient deficiencies, sensitivity to gluten and salt and many more. Several issues could occur based on how the individual interprets the results of their findings, such as excluding certain nutrients with no prior indications of intolerance. 

There is also the idea of a self-fulfilling prophecy.  Individuals who receive resulting showing a high risk for type two diabetes might feel that they are destined to develop the disease so they stop taking precautions to reduce their risk and end up developing the disease.  A study done on identifying SNP’s that are linked to type two diabetes found that some individuals who received a negative result for the presence of diabetes ended up developing the diabetes because they stopped worrying about their diet. Conversely, those that received a positive score changed their lifestyle and decreased the development of insulin resistance2. 

Studies on the psychological effects of predictive genetic testing in Huntington’s disease showed that immediately after learning results there were decreased scores on the General Well-Being Scale and increased depressive symptoms.  When it comes to predictive genetic testing for cancer susceptibility, carriers of the BRCA1 genes mutation reported increased measures in depressive impairment and depressive symptoms.  Interestingly, none of the 41 carriers for the BRCA1 and BRCA2 gene mutations reported having a prophylactic mastectomy by a one-year follow-up and only 17% were considering having the procedure. 

The take away :

When it comes to the debate on nature verse nurture we know that both genetics and environment play a role in pathogenesis and disease progression. With new technologies we are able to identify people at risk earlier and therefore implement interventions that have helped to reduce the risk, prevent disease progression, and ultimately improve mortality and morbidity. More research is needed in the field of Nutrigenomics and personalized nutrition, but the field is fascinating and could be guiding some practice in years to come. Ultimately, genetics does play a role in many disease states, but with a healthy lifestyle and modern technology we can work with our genes, instead of against them, to produce better outcomes. 

References

http://www.dnafiles.org/programs/predictive-genetic-testing/  

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3984860/  https://www.ahajournals.org/doi/full/10.1161/CIRCGENETICS.109.891366

https://www.nejm.org/doi/full/10.1056/NEJM199304223281603

https://www.nature.com/articles/ejcn2012145

http://www.psychosomatic.org/anmeeting/PastEvents/Lerman2002.pdf