Personalized Nutrition: Nutrigenomics
By Ginger Hultin, MS, RDN, CSO
Today’s Dietitian
Vol. 26 No. 1 P. 6

The Future of Personalized Nutrition

The ability to make personalized recommendations through direct-to-practitioner testing has arrived. Personalized nutrition can take many forms, such as RDs recommending and interpreting lab tests, hormones, gut microbiome results, continuous glucose monitoring, and even genetic testing. Research has shown that personalized nutrition, sometimes called precision nutrition or personalization, helps create better client outcomes.1-3 Nutritional genomics is one way RDs are increasingly using personalized nutrition, and it’s been available direct-to-consumer and direct-to-practitioner for a little over a decade. There are challenges and limitations to this type of testing, but there’s also evidence that it can help provide a more personalized approach to health care and lead to more patient compliance with dietary and lifestyle recommendations. Understanding what nutritional genomics is, the latest advances and research, as well as how to use it with clients, is becoming increasingly more important for RDs as it becomes ever more accessible to the public.

Defining Nutrigenomics
The field of nutritional genomics includes nutrigenomics (the influence of nutrients on gene expression) and nutrigenetics (the responses of gene variants to nutrients and diet), both of which can influence phenotype or the observable characteristics of an individual.4,5 Phenotype results from a person’s genetic profile, or genotype, combined with their environment, including diet and lifestyle choices. Nutrigenomics is the most commonly used term when referencing personalized nutrition through genetic testing.

RDs generally have a foundational understanding of some gene/diet challenges from what they learn about inherited metabolic disorders in macronutrient or biochemistry class. For example, phenylketonuria is an inborn error of metabolism caused by a mutation in the phenylalanine hydroxylase gene that leads to an enzyme deficiency. Treatment includes avoiding the dietary amino acid phenylalanine for life.1,6 Another example of a disease that can be identified through genetic testing and has a dietary component to management is hemochromatosis, which causes an individual to absorb too much iron from their diet. It’s identified through variants in the homeostatic iron regulator (HFE) protein gene that causes increased cellular iron uptake, leading to iron overload.4,6 People with hemochromatosis are referred to a physician for treatment and often educated about avoiding iron supplements or consuming iron-fortified foods.

The field of nutrigenomics can provide more personalized insight into diet- and lifestyle-related conditions and chronic illnesses like CVD, type 2 diabetes, obesity, and bone health diseases such as osteoporosis.3,4 Many researchers are hopeful that more knowledge about the human genome will help determine additional benefits to public health. A large review (n=72 studies) by Vyas found that nutrigenomics currently is being used to improve health in regard to cancer, diabetes, CVD, and obesity, as well as to better identify functional foods that are personalized for patients.4

RDs should consider scope of practice when describing nutrigenomics to their clients. For instance, medical genetics, such as testing genes for disease risk like cystic fibrosis, Huntington’s disease, or certain types of cancer, isn’t within an RD’s scope. Patients with this focus should be referred to medical geneticists via their primary care physicians. In contrast, nutrigenomic testing provides helpful data because it gives insight into genes affected by lifestyle factors. RDs can counsel clients about how to optimize their diet or other aspects such as fitness or stress management in ways that can create better outcomes with genetic information.

Latest Advances, Science, and Research
Some of the most important research available isn’t on single nucleotide polymorphisms (SNPs), which are a genomic variant at a single base position in the DNA, or even their influence on disease, but rather the actionability of personalized nutrition data based on genetics to create behavioral changes that benefit health. Studies have shown that nutrigenomic testing can guide dietary recommendations, and when patients receive dietary or lifestyle counseling in addition to personalized genetic information, they experience better outcomes.3,4 Researchers currently are exploring the psychological factors associated with behavioral changes and how best to communicate personalized nutrition in a way that maximizes benefit.8

The landmark randomized controlled trial, Food4Me (n=1,269), investigated personalized nutrigenomic vs generic nutrition advice for dietary behavioral change. After six months, the personalized advice groups implemented and sustained more dietary changes than the control group, such as less red meat, sodium, and saturated fat, and more folate and higher Healthy Eating Index scores. Results from this study and others suggest that personalized nutrition recommendations can improve patient health and diet quality better than generic, general advice.1-3,9

SNP Examples
There are many actionable nutrition-related genes that can be used to counsel clients. These genes aren’t diagnostic but can help elucidate dynamic conversations between RDs and their clients to guide potential health-promoting changes that can be made based on a person’s genetic profile. Lactose intolerance, present in 65% of adults, is linked to a gene that codes for the lactase enzyme not being active or as active in adults as it is in infancy.10 A gene that causes lactose intolerance, lactase (LCT), is generally responsible for lactase nonpersistence or the inability to digest lactose as an adult.5,8 Currently, on direct-to-practitioner and direct-to-consumer tests, LCT genetic SNPs, as well as minichromosome maintenance complex component 6 (MCM6)—which are genetic variants that occur biologically upstream from the LCT gene—can be seen on reports.10 Just because a person has variants in their LCT or MCM6 genes doesn’t mean that a practitioner can say prescriptively, “You’re lactose intolerant.” Nutrigenomic data are not diagnostic. Instead, a practitioner can ask open-ended questions, such as “Do you notice symptoms such as gas, bloating, pain, or diarrhea when you consume dairy?” to open the conversation as they share results.

Genetic SNPs also can be analyzed in relation to each other and how they fit together regarding a person’s risk or predisposition. For example, genetic traits can lead to the up- or down-regulation of biological pathways that could indicate a person may be more likely to develop chronic diseases like diabetes or CVD. When assessing cardiovascular-related genes, consider variants commonly presented in nutrigenomic reports in the fat mass and obesity-associated gene, fatty acid desaturase 1 (FADS1), transcription factor 7-like 2 (TCF7L2), apolipoprotein E , methylenetetrahydrofolate reductase (MTHFR), 5-methyltetrahydrofolate-homocysteine methyltransferase reductase (MTRR), or even caffeine metabolism genes like cytochrome P450 family 1 subfamily A member 2 (CYP1A2).11 This polygenic approach to assessing potential disease risk helps RDs take a holistic approach to how gene variants may help personalize their recommendations.

For example, if patients have a risk variant for some cardiovascular-related genes, dietitians may recommend reducing or eliminating caffeine intake (due to CYP1A2). RDs can ensure clients are meeting B12 and folate requirements in the diet and may suggest their client’s physician order bloodwork to determine homocysteine levels because MTHFR or MTRR can cause B-vitamin metabolism problems in the body. Or, RDs may suggest optimizing their patient’s omega-3 fatty acid intake because FADS1 plays a role in fat metabolism in the body.12-15

Limitations and Future Research
Studies have shown that health care practitioners still exhibit poor knowledge of the field of nutrigenomics and low confidence in their ability to counsel using these personalized data. One of the biggest limitations is that the field of nutritional genomics is still relatively new compared with other types of testing, such as blood labs, and both practitioners and consumers need more education about what it is and how it can improve health.16,17

Currently, nutrigenomic testing isn’t covered by insurance, creating access barriers for RDs and their clients. Many consumers are motivated to self-pay for these tests, but it’s clear there’s a need for greater accessibility and affordability. Many tests are available for $200 or more, and RDs need to charge for their time educating clients about the use of the test and how to complete the test, as well as for the training and onboarding required, the time it takes to prepare for each client, and the time spent directly with each client in addition to follow-up charting, communication, and questions.

Researchers have called for the creation of systems and principles for how best to research nutritional genomics as well as standardized interventions to bring the field into mainstream care.2-4 Using available research and translating it into actionable recommendations and identifying how to use new technology, including machine learning and artificial intelligence, are challenges now facing the field.2 Gathering more data and building databases with increasingly diverse participants are important aspects of the future of understanding nutrigenomics.5

Tips for RDs and Patients
Any RD who’s had a patient ask, “What’s the best diet for me?” likely will be excited and relieved that the era of personalized nutrition through nutritional genomics has arrived and is more accessible than ever. RDs may want to seek additional training in the field, such as with the American Nutrition Association or local universities, so they can counsel patients confidently, but it’s important to understand that RDs already are uniquely educated, credentialled, and qualified to use nutrigenomics in their dietary counseling with appropriate training in the specialty.

— Ginger Hultin, MS, RDN, CSO, is a nutrition and health writer based in Seattle. She owns the concierge nutrition practice Ginger Hultin Nutrition, PLLC, where she practices integrative nutrition care and incorporates nutrigenomic testing for clients.


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