The Science Behind Genetic Tests for Fitness and Nutrition
Genetic tests for fitness and nutrition are being talked about more and more. But what exactly do these tests measure, which findings rest on strong scientific evidence, and where do you need to be careful? In this article, we explain the scientific basis of these tests, the limits of the method and some frequently asked examples in plain language.
What do genetic tests examine?
A large share of the genetic differences between people consists of changes in a single “letter” of DNA; these are called single nucleotide polymorphisms (SNPs), or simply variants. Fitness and nutrition tests examine a selected group of these variants that research has associated with particular traits. A variant being “associated” with a trait does not mean it determines that trait on its own; most traits are shaped by the small contributions of many genes together with lifestyle.
Microarray and imputation: how is the test done?
Most commercial genetic tests analyse DNA obtained from a cheek swab using a microarray (genotyping chip). A microarray does not sequence the whole genome; it reads predefined positions. Some of the reported variants are read directly on the chip, while others are statistically estimated using large reference datasets; this process is called imputation. The accuracy of imputed variants may be lower than that of directly read ones. You can find Hub Genetik’s method and evidence-level approach in detail on our science and safety page.
Why does the level of evidence matter?
Not every genetic association is equally strong. Some are supported by large, replicated studies, while others rely on single or small studies and may not be confirmed by later research. That is why a good report should show the level of evidence (strong, moderate, limited) next to each finding and adjust the wording of its recommendations accordingly.
Examples from fitness
ACTN3 and the power–endurance tendency
The R577X variant of the ACTN3 gene has been associated with power and sprint performance in elite athletes; systematic reviews support this association. Biopsy studies have shown that this variant is also associated with muscle fibre distribution. However, a genetic test does not measure your muscle fibre ratio; this ratio can only be determined by a muscle biopsy. The effect of a single variant on performance is small, and it does not determine which sport suits you.
Injury predisposition
Some variants in connective tissue genes such as COL5A1 have been associated with soft tissue injuries; however, the results of meta-analyses contradict each other. Such findings should therefore be assessed at a “moderate” or “limited” level of evidence and should not replace warming up, load management and recovery in injury prevention.
You can see how sports genetics topics are presented in the report on the Sports & Fitness Genetics page.
Examples from nutrition
Lactase persistence
A variant near the LCT gene is strongly associated with whether the lactase enzyme persists into adulthood. Even so, the cause of digestive complaints should be determined by a physician’s assessment.
Caffeine metabolism
A variant in the CYP1A2 gene is associated with faster or slower caffeine metabolism. Research suggests that the relationship between coffee consumption and heart health, and the effect of caffeine on endurance performance, may differ according to this genotype; these findings are based on a small number of studies.
Vitamin D
Variants in genes such as GC have been associated with blood vitamin D levels. However, your vitamin D level can only be measured with a blood test; a genetic finding does not replace this measurement.
Weight and body mass index
A common variant in the FTO gene is one of the first genetic findings associated with body mass index. Its effect is small on average, and diet and physical activity can change this effect considerably.
How should the results be interpreted?
Genetic test results are one of the pieces of information you can take into account when planning training and nutrition; on their own, they do not determine which sport suits you, your vitamin needs or your disease risk. The healthiest approach is to review the results together with your coach, dietitian or physician and to try them out in small, measurable steps. You can see how findings, evidence levels and recommendations are presented together in a report on our sample report page.
References
- Yang N, MacArthur DG, Gulbin JP et al. ACTN3 genotype is associated with human elite athletic performance. Am J Hum Genet 2003. PMID: 12879365. doi:10.1086/377590
- Ma F, Yang Y, Li X et al. The association of sport performance with ACE and ACTN3 genetic polymorphisms: a systematic review and meta-analysis. PLoS One 2013. PMID: 23358679. doi:10.1371/journal.pone.0054685
- Vincent B, De Bock K, Ramaekers M et al. ACTN3 (R577X) genotype is associated with fiber type distribution. Physiol Genomics 2007. PMID: 17848603. doi:10.1152/physiolgenomics.00173.2007
- Guo R, Ji Z, Gao S, Aizezi A et al. Association of COL5A1 gene polymorphisms and musculoskeletal soft tissue injuries: a meta-analysis based on 21 observational studies. J Orthop Surg Res 2022. PMID: 35241120. doi:10.1186/s13018-022-03020-9
- Fukuyama Y, Murakami H, Iemitsu M. Single Nucleotide Polymorphisms and Tendon/Ligament Injuries in Athletes: A Systematic Review and Meta-analysis. Int J Sports Med 2024. PMID: 39437988. doi:10.1055/a-2419-4359
- Enattah NS, Sahi T, Savilahti E et al. Identification of a variant associated with adult-type hypolactasia. Nat Genet 2002. PMID: 11788828. doi:10.1038/ng826
- Cornelis MC, El-Sohemy A, Kabagambe EK, Campos H. Coffee, CYP1A2 genotype, and risk of myocardial infarction. JAMA 2006. PMID: 16522833. doi:10.1001/jama.295.10.1135
- Guest N, Corey P, Vescovi J, El-Sohemy A. Caffeine, CYP1A2 Genotype, and Endurance Performance in Athletes. Med Sci Sports Exerc 2018. PMID: 29509641. doi:10.1249/MSS.0000000000001596
- Wang TJ, Zhang F, Richards JB et al. Common genetic determinants of vitamin D insufficiency: a genome-wide association study. Lancet 2010. PMID: 20541252. doi:10.1016/S0140-6736(10)60588-0
- Frayling TM, Timpson NJ, Weedon MN et al. A common variant in the FTO gene is associated with body mass index and predisposes to childhood and adult obesity. Science 2007. PMID: 17434869. doi:10.1126/science.1141634