The Human Genome Project, completed in 2003, laid the groundwork for scientific research on the environment’s influence on gene expression. This led to the increased popularity of nutrigenomics, the field of discovery about how environmental factors, such as food intake and lifestyle, influence gene expression.
Through ongoing studies, researchers and health professionals are learning more about how food affects gene interactions. Further, the differences in genes among people affects nutrient requirements, metabolism and the response to nutrition and dietary interventions, necessitating personalized recommendations. For example, common variants in genes regulating homocysteine metabolism have been linked to blood folate and homocysteine levels, possibly influencing cardiovascular disease risk and neural tube defects. Single nucleotide polymorphisms, or SNPs, are small changes in DNA sequencing that result in genetic variations, such as in the vitamin D receptor gene which can alter vitamin D availability. An SNP has been linked to a predisposition for osteoporosis in postmenopausal women with low calcium intake.
Much research surrounds weight and obesity as they relate to genes and lifestyle. Studies indicate that 40 percent to 70 percent of variability between individuals in body mass index may be attributed to genetic factors. In the future, genetic testing may become routine for specific dietary advice for weight loss but currently is not practical because of complex gene-environment interactions and because likely hundreds of genes are involved in determining weight.
A 2014 Academy of Nutrition and Dietetics position paper stated that nutritional genomics provides insight into how diet and genotype interactions affect phenotype. Proponents believe health care can be improved if practitioners can provide nutrition recommendations that are more personalized than population guidelines, based on genetic profile, phenotype, health status, food preferences and environmental factors. However, because gene expression is constantly interacting with the changing environment, it is not possible to counsel patients using genetic information alone.
For example, someone could have a variant in the methylenetetrahydrofolate reductase, or MTHFR, gene but have normal homocysteine levels, or vice versa. A mutation in a single gene can result in a specific disorder, but chronic diseases such as cardiovascular disease and diabetes are related to many genes. Clients should be educated on how their genes interact with their environment and dietary and lifestyle choices.
Regulation and Areas of Research
In 2005, the International Society of Nutrigenetics/Nutrigenomics, or ISNN, was founded to regulate the field and increase the understanding of the role of genetic variation and dietary response. Regulation is necessary to protect consumers and health care professionals alike. For example, it could be considered unethical for a registered dietitian nutritionist to counsel a patient on genetics that are medical in nature and do not have a nutrition or lifestyle connection. Women may inquire about testing for the breast cancer susceptibility genes (BRCA1 and BRCA2), but this type of counseling should be referred to a medical geneticist who can interpret risk and discuss treatment options or surgery based on the individual’s needs.
According to the Academy’s 2014 position paper, several single gene mutations have been linked to severe obesity but only in a fraction of the population. The various fat mass- and obesity-associated genes, or FTOs, have the strongest known effect on adiposity and obesity risk. People with a specific FTO gene variant have been shown to weigh an average of 6.6 pounds more and were nearly two times more likely to be obese than those without the variant. Studies show a stronger positive correlation between FTO and obesity among individuals with higher intakes of sugar-sweetened beverages and fried foods compared to those with lower intakes. Some research has shown high-protein, hypocaloric diets consumed by participants with FTO variants caused reduced food cravings and appetite scores. However, obesity is polygenic, involving several genes and environmental interactions that are affected by lifestyle behaviors. People genetically predisposed to obesity can maintain a normal BMI through appropriate diet and physical activity which can be personalized with the help of an RDN.
Some studies suggest knowledge of having an FTO risk allele encourages greater behavior change than nutrition education alone. The Food4Me clinical trial found greater changes in adiposity markers in the experimental group who knew they carried the FTO risk allele than in the control group who were not provided genetic information.
Controversy in Nutrigenomics
Although evidence is strong for some gene-diet associations, others remain unclear, which is one reason why the implementation of nutrigenomics remains controversial. Some health care professionals argue that nutrigenomics is not ready for clinical use or that much of the evidence comes from observational studies. Others are practicing outside of what current research supports. It is inappropriate and perhaps unsafe to counsel patients on changing their diets or lifestyles based on genetics without considering individual clinical biomarkers, dietary and lifestyle preferences and ability to make changes. Because of the complexity of the interaction between genes and environmental factors and the hundreds of genes that play a role in chronic disease, it may never be possible to prescribe a specific diet based on genetics alone.
Other health care professionals fear that using a nutrigenomic approach will not achieve better results than current nutrition counseling methods. One study showed a nutrigenomic-based diet did not increase weight loss compared to a standard balanced diet. A 2016 meta-analysis found no significant effects of communicating DNA-based risk estimates on diet or physical activity. Another study showed that knowledge of the MTHFR genotype did not significantly improve dietary folate intake.
Some studies show promise that genetic information could pique client interest. A study on the FADS1 gene and intake of omega-3 fatty acids showed that although education to participants in the experimental group did not appear to increase omega-3 intake compared to the control group, the educated participants reported greater awareness of omega-3 terminology. They also rated cost as a barrier to omega-3 consumption less than the control group and reported the nutritional information about omega-3s as more useful.
Role of the RDN
Registered dietitian nutritionists must obtain basic competency in genetics before entering the field of nutrigenomics. To personalize medical nutrition therapy and analyze disease risk, RDNs must use reliable testing methods and consider factors that affect genetic mutations. Family history, biochemical parameters and lifestyle risk factors still should be used when personalizing dietary interventions when working with nutritional genomics. In the future, RDNs may be able to interpret nutrigenomics to make more personalized nutrition recommendations and help promote increased client understanding and motivation to change.