What does Consumer Genetic Testing Say about Fitness and Trainability?

Shannon Miller

August 22, 2019

In our ever-evolving age of information, the promise of using DNA to answer many of our health questions incredibly intriguing. If we know which genes we have, and which genes we don’t have, we can know more about how to plan for the future. But is the science really there yet? Heather Huntsman, Ph.D. CSCS, explains why it may be too soon to rely on direct-to-consumer genetic testing to inform decisions around fitness and trainability.

For those of us who are constantly searching for the “best” options for our health (e.g. the best diet or the best workout strategy) why wouldn’t we look to our genes to understand how we are built and what is our actual health potential? This is what the companies that sell at-home genetic tests promise, right?

We’re starting to hear a lot more about these tests, with cost becoming more reasonable to the average consumer. If you’ve done your research, you’ve also read that scientists have identified genes for breast cancer, cystic fibrosis, and muscular dystrophy.1 What’s more, online resources show that you can even learn more about your body’s preference for carbohydrates over fat, or muscle building potential, body composition, and athletic potential. If you can afford the test, why wouldn’t you want to have personalized answers to some of your most important health questions? It seems like a no-brainer.

While I hate to be always be the cynic in the room, as a scientist, I feel responsible for making sure I communicate the most accurate information available, delivered in a way that helps you make the best decisions for your health. The truth is, similar to my advice about wearables, while the underlying science is strong and we are learning more about what genes do and how they are regulated, once again, the business model driving this technology is stretching the science slightly beyond the data.2

The problem is that genetics is a much more complicated equation than “gene x” results in “trait y.” Yes, who we are is a result of our genes, BUT which genes are expressed, and at what level they are expressed is a VERY complicated process.3

While I won’t go into all of the factors that are important in gene expression and regulation, it is important to know that your environment and genetic background (i.e. all of the other genes that make up you) play a huge role in the expression and interpretation of the genes that these tests screen for.4 What does that mean? It means that excluding a small number of genetic diseases that actually follow the “gene x” equals “trait y” math, the more complex the trait, the less is known about all the genes involved.3,4 So, for things like metabolism and athletic performance where several cellular pathways are involved, we know very little about the genes driving these physiological processes.3

As much as I want to tell you that we have all the answers, our understanding of genetics just isn’t there yet. And even if it were, and I can’t communicate this enough, you are not simply the product of your genes. The real equation looks more like:

Gene x + Gene regulators in the DNA + Epigenetics + Environment + Ancestry + Lifestyle choices = Trait y 3,4

My advice: read your results with caution.2,3,5 While I don’t think these companies are intentionally trying to give out misinformation, remember that for many of the questions they are trying to answer, we just don’t have enough information yet.6 At this point a lot the “answers” they give are indirect associations at best.2,3,4

So, what’s your best bet? Get to know your body through proven methods of scientific testing (like body composition analysis, resting metabolic rate testing, and VO2 Max testing) and use your data to make the “best” health decisions for your body now.


  1. Allyse MA, Robinson DH, Berber MJ et al. (2018) Direct-to-Consumer Testing 2.0: Emerging Models of Direct-to-Consumer Genetic Testing. Mayo Clinic Proceedings 93:1:113-120.
  2. Khoury MJ. (2017) Direct to Consumer Genetic Testing: Think Before You Spit, 2017 Edition! Centers for Disease Control and Prevention. https://blogs.cdc.gov/genomics/2017/04/18/direct-to-consumer-2/
  3. Joyner MJ. (2019) Limits to the Evidence that DNA Sequence Differences Contribute to Variability in Fitness and Trainability. Medicine & Science in Sport and Exercise 51(8):1786-1789.
  4. Genetics Home Reference. (2019) Help Me Understand Genetics: Direct-to-Consumer Genetic Testing. S. National Library of Medicine. https://ghr.nlm.nih.gov/primer/dtcgenetictesting/directtoconsumer
  5. About Genomics. (2019) 15 for 15: Direct-to-Consumer Genomic Testing. National Human Genome Research Institute. https://www.genome.gov/dna-day/15-for-15/direct-to-consumer-genomic-testing
  6. Bouchard C. (2019) DNS Sequence Variations Contribute to Variability in Fitness and Trainability. Medicine & Science in Sport and Exercise 51(8):1781-1785.


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