Which is more likely to give you expert, individualized results to meet your goals : personalized nutrition advice from a dietitian or the newest at-home genetic test? A nutrition expert answers all your questions.
Nutrigenetics, or the study of how genes affect nutrition, is a topic of increased consumer interest. Millions of people have completed direct-to-consumer (DTC) testing to determine genetic information about their health and nutrition. So how exactly does genetic information relate to nutrition care, counseling, dietary outcomes, and precision nutrition?
In a nutshell, nutrigenetics, at-home testing, and direct-to-consumer genetic testing are all relatively new and unstandardized forms of nutrition care. Integrating a nutrition expert and dietitian is currently the best evidence-based way to receive personalized nutrition counseling and identify dietary outcomes.
Read on to explore more about consumer trends in nutrition care.
What is nutrigenetics?
Nutrigenetics is the study of how gene variations can influence nutrition, which can alter disease risk over time. Nutrient factors such as the following can be influenced by genes:
Intake
Metabolism
Absorption
Utilization
Ultimately, genetic variations can contribute to altered biochemical indicators or anthropometric values, which are basically measures that identify disease risk.
How do genes influence nutrition?
Genes and nutrition are both important aspects of health. There are two major areas of study that explore nutrition and genes. One is nutrigenetics, which studies how genes affect nutrition, and the other is nutrigenomics, which is the study of how diet affects gene expression.
The following graphic helps to illustrate the relationship between genes and nutrition.
Your diet (an environmental factor or exposure), genetic background, and epigenome influence overall health. The epigenome is simply a collection of the different cellular markers or modifications on the DNA of a cell. For example, liver cells and blood cells have different epigenetic marks.
Dietary patterns introduce bioactive compounds into the body. The body then metabolizes these compounds into products it can use. Depending on what you eat and your dietary patterns over time, the composition of your microbiome (gut bacteria) and metabolism (the way food is broken down) can change. Ultimately, this process results in changes to gene expression, meaning DNA can be altered -- for better or worse -- based on what you eat.
What is “precision nutrition”?
Precision nutrition is the practice of personalized nutrition. It refers to a tailored nutrition prescription that is used as an approach to both prevent or manage disease, especially metabolic diseases.
There are several main factors to take into account when considering precision nutrition. They include:
Nutrigenomics - how diet affects gene expression
Microbiota
Metabolomics - the study of metabolites in an organ, tissue, or cell
Deep phenotyping - precise and comprehensive analysis of phenotype components in order to yield individualized information
Dietary habits
Food behaviors
Physical activity
Within precision nutrition, there are three levels:
Stratified Nutrition- conventional guidelines into population subgroups (i.e. age, gender)
Individualized Nutrition- guidelines from deep, refined phenotyping
Genotype-Directed Nutrition - guidelines based on gene variability
Genotype-directed nutrition can be extremely helpful because of its high level of impact on an individual's health. The potential of response for that individual to particular foods can be fine tuned to meet their exact needs. However, there are some downsides:
High cost
Time-consuming
Specialized training needed for efficient use
Intensive clinical measurements
Accurate evaluation by a trained professional
Metabolotyping helps to group metabolically similar individuals into stratified categories. This helps identify how individuals respond differently to similar nutritional interventions. Instead of starting at the genotype-directed nutrition level, stratified nutrition helps to manage costs while also providing subgroups with more individualized information.
Even at the stratified level, precision nutrition can help to predict:
Individual responses
Nutrient requirements
Predisposition to food tolerances or intolerances
Which is more important, genes or nutrition?
Amy Myers, M.D. answers this question perfectly in her book The Autoimmune Solution:
“Yes, there is a genetic component to autoimmune disorders. However, twin studies have shown that autoimmunity is only 25 percent heritable, which means that the environment is a far more significant part of the picture: 75 percent to be exact.
“...we have learned from the brand-new field of epigenetics, genetic expression can be modified. Certainly you cannot change your genes. You can, however, turn some genes on while turning others off, thereby changing your genetic expression -- the extent to which your genetic qualities are actually expressed.
“Yes, there is a genetic component to your illness. But those genes are not the whole story.”
As Myers goes on to explain, diet is an environmental factor that can be modified. In other words, a healthy dietary pattern can be so powerful that it contributes to turning problematic genes off.
Direct-to-Consumer and At-Home Testing
An estimated 26 million people have completed direct-to-consumer testing. It is an area of increased interest in precision nutrition. Medical professionals are increasing the routine use of genetic sequencing in health care for risk of diseases such as cancer.
When it comes to genetic testing, who knows best -- dietitians or direct-to-consumer tests?
Registered dietitian nutritionists (RDNs) are considered the most reliable source of personalized nutrition among the general population. Genetic testing has significant limitations, even though up to 91% of people studied report willingness to follow a personalized diet.
When is genetic testing appropriate?
Genomic factors have not been standardized in nutrition counseling, with the exception of monogenic diseases (i.e. rare forms of diabetes resulting from mutations or changes in one single gene). In these cases, correct diagnosis is crucial to proper treatment (i.e. better glucose control, improved long-term health).
Testing can also be important for individuals with certain conditions that are planning for pregnancy. Some conditions carry a risk of having a child with the same condition, and it can be important to prepare for the most appropriate treatment in advance.
What is involved in genetic testing?
Genetic tests can differ, however most involve providing a sample of blood or saliva. From these samples, DNA is isolated and tested in specialized labs. It is analyzed for changes in genes to determine the cause of health concerns.
Should I share my genetic testing results with my dietitian?
Fun fact: more people report that they would share their results with a dietitian than would share their results with their life partner. Sharing your results is a personal decision. As stated before, there is no standardized policy or procedure for genetic testing in nutrition care.
According to recent research, dietitians are still considered the most reliable source of personalized information about nutrition. Your genetic testing may reveal risk factors, but a dietitian can help you act on them in appropriate, applicable, and safe ways.
Dietitians are trained to interpret many standard measures of health, and can help you find a balanced approach to eating based on multiple factors -- not just genetics.
What do dietitians need to know about genetic and direct-to-consumer testing?
In a recent article of Today’s Dietitian, three excellent points of guidance for best practice are provided:
Research the genetic testing company. Who are the genetic testing partners? Is the lab certified by the Clinical Laboratory Improvement Amendments (CLIA) or accredited by the College of American Pathologists (CAP)? Are the genes tested AND the research used to make assessments available in a public report?
Avoid companies that try to diagnose clients. What credentials and experience does the company’s scientific advisory board have? Is there a sample report available to review for thoroughness and ease of use? Are reports and recommendations combined, creating a potential conflict of interest?
Interpret DNA tests cautiously. Understand that the tests aren’t diagnostic and show ONLY predispositions. Be sure to emphasize this understanding with clients, and combine traditional assessment measures and clinical presentation with DNA testing. For example, genetic testing showing a predisposition for nutrient deficiency is not enough to establish an actual deficiency. Supplements should not be recommended until after standardized best practice measures have been conducted.
If clients ask for a direct-to-consumer test recommendation, what should I say?
It is up to your code of conduct and ethics agreements, but as long as you make sure that your client understands the risks and benefits of a DTC it should be appropriate to recommend a product you have thoroughly researched. If you have any questions or doubts about a company or brand, be sure to research or reach out directly to the genetic testing company before incorporating them into your practice.
Is there a direct-to-consumer test you recommend as a nutrition professional?
As a nutrition expert, I generally make sure clients and consumers understand the limitations of genetic testing before making a recommendation. In my personal practice, if people are interested in testing I refer them to 23andMe. They market the only four DTC tests that have received authorization by the FDA. This means they have undergone FDA evaluations for accuracy, reliability, and consumer comprehension.
Genetic testing can yield potentially helpful tests in determining predisposition -- but remember, these aren’t definitive or diagnostic of nutrition problems. They may be helpful in individual cases to determine the next best course of action or the most appropriate treatment.
The following are indicated conditions for which the 23andMe Personal Genome Service (PGS) has been authorized and may be helpful to guiding nutrition care:
Bloom Syndrome (carrier screening test)
BLMAsh variant in the BLM gene
Hereditary Thrombophilia (General Health Risk Report)
Factor V leiden variant in the F5 gene
Prothrombin G20210A variant in the F2 gene
Alpha-1 Antitrypsin Deficiency (Genetic Health Risk Report)
PI*Z and PI*S variants in the SERPINA1 gene
Late-onset Alzheimer's Disease (Genetic Health Risk Report)
ε4 variant in the APOE gene
Parkinson's Disease (Genetic Health Risk Report)
G2019S variant in the LRRK2 gene
N370S variant in the GBA gene
Gaucher Disease Type 1 (Genetic Health Risk Report)
N370S, 84GG, and V394L variants in the GBA gene
Factor XI Deficiency (Genetic Health Risk Report)
variants F283L, E117X, IVS14+1G>A in the F11 gene
Celiac Disease (Genetic Health Risk Report)
variant associated with the HLA-DQ2.5 haplotype
Glucose-6-Phosphate-Dehydrogenase Deficiency
Val68Met variant in the G6PD gene
Hereditary Hemochromatosis (Genetic Health Risk Report)
C282Y and H63D variants in the HFE gene
Early-Onset Primary Dystonia (DYT1/TOR1A-Related) -- (Genetic Health Risk Report)
deltaE302/303 variant in the DYT1 gene
BRCA1/BRCA2 (Selected Variants) -- Breast, Ovarian, and Prostate Cancer (Genetic Health Risk Report)
185delAG and 5382insC variants in the BRCA1 gene
6174delT variant in the BRCA2 gene
Pharmacogenetic Reports
For the majority of these genetic tests, variants indicate increased but not overall risk. Another limitation is that the reports are most relevant for certain populations. Pharmacogenetic reports can help describe the likelihood of response to a particular therapeutic.
These tests are not to be used as a substitute for health care provider visits or to start, stop, or change any current course of treatment.
I recommend the Health + Ancestry Service from 23andMe if you are looking for reports that include the above listed information.
The Bottom Line
While direct-to-consumer tests (DTC) can be helpful and provide information about genetic predispositions, they are not yet authorized for standardized nutrition care. By definition, DTCs bypass the involvement of a health care provider. Dietitians should be sure to avoid companies claiming to diagnose, thoroughly research genetic testing companies, and use caution in interpreting DNA results when clients involve genetic testing in the nutrition care process.
Resources
The following are helpful and reliable health organization pages that can provide further guidance on this topic:
Centers for Disease Control and Prevention (CDC) - Consumer Genetic Testing Is Booming: But What are the Benefits and Harms to Individuals and Populations?
Food and Drug Administration (FDA) - Direct to Consumer Tests (Includes lists of DTC tests with marketing authorization as well as FAQs)
U.S. National Library of Medicine, National Institutes of Health (NIH) - What is direct-to-consumer genetic testing? and What does it mean to have a genetic predisposition to a disease?
Academy of Nutrition and Dietetics (AND) - Consensus Report on Incorporating Genetic Information into Nutrition Care
References
Bordoni L, Gabbianelli R. Primers on nutrigenetics and nutri(epi)genomics: Origins and development of precision nutrition. Biochimie. 2019;160:156-171.
de Toro-Martín J, Arsenault BJ, Després JP, Vohl MC. Precision Nutrition: A Review of Personalized Nutritional Approaches for the Prevention and Management of Metabolic Syndrome. Nutrients. 2017;9(8):913. Published 2017 Aug 22. doi:10.3390/nu9080913
Delude CM. Deep phenotyping: The details of disease. Nature.com. Published November 4, 2015.
Food and Drug Administration. Direct-to-Consumer Tests. Fda.gov. Published December 20, 2019.
Mills S, Stanton C, Lane JA, Smith GJ, Ross RP. Precision Nutrition and the Microbiome, Part I: Current State of the Science. Nutrients. 2019; 11(4):923. https://doi.org/10.3390/nu11040923
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Monogenic Diabetes (Neonatal Diabetes Mellitus & MODY). Niddk.nih.gov. Published November 2017.
Robinson K, Rozga M, Braakhuis A, Sinley R, Wanner A, Vargas AJ. Effect of Incorporating Genetic Testing into Nutrition Counseling and Care on Dietary Intake: An Evidence Analysis Center Systematic Review -- Part I. J Acad Nutr Diet. 2021;121(3):553-581.
Weisenberger J. Update on Genetic Testing. Today’s Dietitian. 2019;21(5);36.
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