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The NHS recently released a strategy for accelerating its use of genomic medicine over the next 5 years (NHS England, 2022).  Meanwhile direct-to-consumer (DTC) genetic testing whereby consumers send a saliva swab to genotyping companies for insights into their health, genetic predisposition, or ancestry, without involving a healthcare provider, is also a rapidly growing market predicted to be worth $2.7billion by 2025 (Government Office for Science, 2022).  An increasing number of these companies offer nutrition recommendations based on this genotyping, known as nutrigenetic testing.  

Nutrigenetic testing is available on 137 different single nucleotide polymorphisms (SNPs) ranging from vitamin and lipid metabolism to bitter taste and caffeine, salt, and lactose sensitivity (Floris et al., 2020).  As an example, individuals with a SNP at rs1801133 on the methylenetetrahydrofolate reductase (MTHFR) gene have one or more T alleles rather than C alleles.  This reduces the activity of the MTHFR enzyme, reducing the activation of folate and conversion of homocysteine to methionine, resulting in higher levels of homocysteine in the blood, linked to increased risk of cardiovascular disease (Wald et al., 2011).  This is an example of a nutrient gene interaction; these individuals may benefit from increasing their dietary folate to to reduce their risk of cardiovascular disease.  However, evidence on the effect of folate supplementation for individuals with this SNP on CVD risk is mixed, possibly due to obfuscation from mandatory flour fortification, the simultaneous use of therapies such as asprin and other confounding factors such as race, age, sex, and smoking (Jin et al., 2018).  It is a similar issue for many other SNPs.  The quality of the studies which comprise the evidence varies considerably, as do their sample sizes, durations, populations, and study types.  The critical analysis of the evidence for the link between a SNP and its interaction with a nutrient is therefore far from straight forward.

A framework to assess the scientific validity and evidence for dietary advice based on genotype was produced by a group of experts in nutrigenetic research (Grimaldi et al., 2017).  This outlines criteria for the quality of studies included in the evidence, the number of studies and sample sizes required, and requirements for biological plausibility and the nature of the gene nutrient interaction.  However, transparency around the SNP selection process varies considerably between DTC nutrigenetic testing companies; while some describe a framework like that outlined above others simply provide one or two citations for each SNP without any evaluation of the quality of the study.

Once a nutrient gene interaction has been established, there remains a question as to the appropriate nutritional recommendation.  Clinical utility was addressed in a subsequent paper published earlier this year, which developed the first two clinical practice guidelines for nutrigenetics related to omega 3 intake for individuals with SNPs that mean their triglyceride levels respond favourably (Keathley et al., 2022).  This also set out a framework for developing further guidelines, although their view is that much of the evidence in nutrigenetics currently isn’t ready for implementing into clinical practice. It is hoped that further guidelines will follow once more systematic reviews are published, and DTC genotyping companies will be able to incorporate these into their reports as validated recommendations.  In the meantime, although there is mixed evidence as to whether adding nutrigenetic testing improves the effectiveness of personalised nutrition advice (Celis-Morales et al., 2017; Jinnette et al., 2021), trials have supported the effectiveness of genetic information in reducing salt intake and discretionary food intake (Nielson et al., 2014; Livingstone et al., 2021), and this remains an area of interest and research.   

If you would like to learn more about nutrition and lifestyle interventions for supporting health and wellbeing and preventing chronic disease, please check out the Nutritank website and join our community to learn more.  And look out for our upcoming related post on Nutrigenomics – how nutrients affect gene expression. 

References

Celis-Morales, C., Livingstone, K. M., Marsaux, C. F. M., Macready, A. L., Fallaize, R., O’Donovan, C. B., Woolhead, C., Forster, H., Walsh, M. C., Navas-Carretero, S., San-Cristobal, R., Tsirigoti, L., Lambrinou, C. P., Mavrogianni, C., Moschonis, G., Kolossa, S., Hallmann, J., Godlewska, M., Surwillo, A., . . . Mathers, J. C. (2017). Effect of personalized nutrition on health-related behaviour change: evidence from the Food4Me European randomized controlled trial. International Journal of Epidemiology, 46(2), 578-588. 

Floris, M., Cano, A., Porru, L., Addis, R., Cambedda, A., Idda, M. L., Steri, M., Ventura, C., & Maioli, M. (2020). Direct-to-Consumer Nutrigenetics Testing: An Overview. Nutrients, 12(2), 566. 

Government Office for Science. (2022). Genomics Beyond Health – full report. https://www.gov.uk/government/publications/genomics-beyond-health/genomics-beyond-health-full-report-accessible-webpage#fn:7 [Accessed 25/11/2022]

Grimaldi, K. A., van Ommen, B., Ordovas, J. M., Parnell, L. D., Mathers, J. C., Bendik, I., Brennan, L., Celis-Morales, C., Cirillo, E., & Daniel, H. (2017). Proposed guidelines to evaluate scientific validity and evidence for genotype-based dietary advice. Genes & Nutrition, 12(1), 1-12.

Hietaranta-Luoma, H., Tahvonen, R., Iso-Touru, T., Puolijoki, H., & Hopia, A. (2014). An intervention study of individual, apoE genotype-based dietary and physical-activity advice: impact on health behavior.Lifestyle Genomics, 7(3), 161-174.

Homocysteine Lowering Trialists’ Collaboration. (2005). Dose-dependent effects of folic acid on blood concentrations of homocysteine: a meta-analysis of the randomized trials. The American journal of clinical nutrition82(4), 806-812.

Horne, J. R., Nielsen, D. E., Madill, J., Robitaille, J., Vohl, M., & Mutch, D. M. (2022). Guiding global best practice in personalized nutrition based on genetics: the development of a nutrigenomics care map. Journal of the Academy of Nutrition and Dietetics, 122(2), 259-269.

Jin, H., Cheng, H., Chen, W., Sheng, X., Levy, M. A., Brown, M. J., & Tian, J. (2018). An evidence-based approach to globally assess the covariate-dependent effect of the MTHFR single nucleotide polymorphism rs1801133 on blood homocysteine: a systematic review and meta-analysis. The American Journal of Clinical Nutrition107(5), 817-825.

Jinnette, R., Narita, A., Manning, B., McNaughton, S. A., Mathers, J. C., & Livingstone, K. M. (2021). Does personalized nutrition advice improve dietary intake in healthy adults? A systematic review of randomized controlled trials.Advances in Nutrition, 12(3), 657-669. 

Keathley, J., Garneau, V., Marcil, V., Mutch, D. M., Robitaille, J., Rudkowska, I., Sofian, G., Desroches, S., & Vohl, M. (2021). Clinical practice guidelines using grade and agree II for the impact of genetic variants on plasma Lipid/Lipoprotein/Apolipoprotein responsiveness to omega-3 fatty acids. Frontiers in Nutrition, 8

Livingstone, K. M., Celis-Morales, C., Navas-Carretero, S., San-Cristobal, R., Forster, H., Woolhead, C., O’Donovan, C. B., Moschonis, G., Manios, Y., Traczyk, I., Gundersen, T. E., von, C. A., Marsaux, C. F. M., Fallaize, R., Macready, A. L., Daniel, H., Saris, W. H. M., Lovegrove, J. A., Gibney, M., . . . Food4Me, S. (2021). Personalised nutrition advice reduces intake of discretionary foods and beverages: findings from the Food4Me randomised controlled trial.The International Journal of Behavioral Nutrition and Physical Activity, 18(1), 1-70. 10.1186/s12966-021-01136-5

NHS England. (2022). Accelerating genomic medicine in the NHS. Available at: https://www.england.nhs.uk/long-read/accelerating-genomic-medicine-in-the-nhs/ [Accessed 25/11/2022]

Nielsen, D. E., & El-Sohemy, A. (2014). Disclosure of genetic information and change in dietary intake: a randomized controlled trial. PloS One,9(11), e112665. 

Wald, D. S., Morris, J. K., & Wald, N. J. (2011). Reconciling the evidence on serum homocysteine and ischaemic heart disease: a meta-analysis. PloS one6(2), e16473. 

Rebecca Hillier

Rebecca has recently completed an MSc in Human Nutrition at St Mary’s University and will soon be registering with the AfN as a Registered Associate Nutritionist. She particularly enjoyed the optional Nutrigenomics module of the master’s programme and for her dissertation investigated the association between genetics, taste perception and preferences and dietary intake, running tasting sessions with 50 participants. She has a passion for food and understanding how it affects health and is now looking to pursue a career in personalised nutrition.