Can Analyzing Your Spit and Blood Make You a Better Athlete?

When Jennifer St. Jean complained of constant fatigue, her doctor dismissed her concerns as the consequence of parenting two kids. "But the kind of fatigue I had wasn't normal for a mom," she says. St. Jean, a competitive runner, had also been feeling sluggish during her training—unable to explain why her pace kept trending upward or her finishing kick disappeared. She was only 42, and in good shape. Something was off.

St. Jean thought a blood test might reveal some answers. In the past, this would have been available only to pro athletes or a relatively expensive process, involving a visit to a sports performance lab or specialist. But a growing number of new testing services claim to make it easy for data-hungry athletes to gain a competitive edge. Unlike traditional diagnostic assessments, which screen for disease risk, these tests claim they match your unique biochemistry and genetic profile with personalized nutrition and training advice.

"By understanding which [biomarkers] are moving and how they're moving, [the test] informs your training approach in a more productive way," says Richard Schwabacher, who launched Blueprint for Athletes, a blood analysis product offered by Quest Diagnostics.

Thanks in part to this increased interest in body monitoring, the market for direct-to-consumer lab tests surged from $15.3 million in 2010 to $131 million in 2015, according to market research firm Kalorama Information.

Critics, however, worry that businesses are getting ahead of scientific data. The tests still aren't cheap, either, running several hundred dollars depending on the number of biomarkers or genes tested. In the case of blood tests, which most companies suggest repeating several times a year, it's an ongoing investment, too.

St. Jean went with InsideTracker, a relatively new company founded in 2009 that says it offers "science-based blood analytics." Her results suggested that she might be training too hard. The report said her liver enzymes and creatine kinase levels were high, which can be a side effect of muscle damage or tissue breakdown due to strenuous exercise. It also said she had low ferritin levels, a measure of the body's iron stores and capacity to transport oxygen.

Without that evidence, she says, "I would have thought there was something wrong with my training and [I] needed to work harder and do more long runs."

Based on those results, St. Jean incorporated more rest and restorative yoga into her routine. She also adjusted her diet, focusing on iron-rich foods to increase her ferritin stores. And in this case, it seems to have worked: She's running faster than ever as a master, closing in on the 1500-meter personal best she set when she was 23.

But while the tests helped St. Jean, the science behind these diagnostics is still evolving. It's important to understand exactly what they look at and what the results mean.

Companies like InsideTracker and Blueprint for Athletes analyze vials of blood and claim to report if your biomarkers are high or low based on your needs as an athlete, which may be different from what's considered normal for a general population.

"If some biomarkers look poor, I know they're either training too hard or not getting enough food to feel their best on race day," says Mike Ormsbee, a professor of nutrition and exercise sciences at Florida State University. For example, low levels of vitamin B12—key for metabolism, red blood cell production, and nerve function—are linked to fatigue, Ormsbee says. Changes in cortisol and testosterone levels may mean you're overtraining. Tests also claim they can uncover food sensitivities, too—such as lactose intolerance or gluten sensitivity.

Other tests like DNAFit, Nutrigenomix, and others, meanwhile, aim to assess genetic markers that may affect how you respond to exercise and nutrition, based on saliva samples. Typically, these are identified as a variation at a single point in your DNA sequence. "That difference may lead to a difference in the function of the gene," says Mark Sarzynski, a professor of exercise science at the University of South Carolina. For instance, the test might show you don't fully metabolize Vitamin D and may need more aggressive supplementation. Or maybe you're predisposed to respond better to endurance training than to power training.

Companies say the recommendations are based on published research in scientific journals vetted by their advisory boards. However, most of the research is still in the early stages, and there's currently no regulation or uniform standards. "I don't think the science is yet at the level where we can make any recommendations based on an individual's genetic profile," Sarzynski says. "Who within the company is choosing the markers, who is interpreting the evidence, and who is making the recommendations?" he asks.

For example, some companies might have a weak advisory board—members who don't have a MD or PhD or relevant research experience, including interpreting scientific studies, Sarzynski says. Other members may be window dressing and not actually involved in the company's research and development. Nanci Guest, a sports dietitian and PhD candidate at the University of Toronto who advises Nutrigenomix, has seen companies interpret data from her lab incorrectly and provide recommendations that were opposite of her findings. Other companies may rely on a proprietary computer algorithm to match your profile to suggested dietary, exercise, and lifestyle changes.

"Genetics is complex," Sarzynski says. In studies that have been done, the sample sizes are often small, and the research protocols weren't meant to be scaled to the general population. "Almost all of these studies were not originally designed to test for the genetics of exercise response," he says. "We should interpret these results with caution until randomized controlled trials are performed."

The tests haven't always fared well under close scrutiny, either. A 2015 meta-analysis of research behind nutrigenomic tests found "[n]o specific—and statistically significant—association was identified for any of the 38 genes of interest. In those cases, where a weak association was demonstrated, evidence was based on a limited number of studies." And while another recent study did find that those who received personalized nutrition advice, including based on their genetic make-up, were healthier than those who received generic dietary advice, the researchers were quick to note that the "clinical relevance is modest."

In fact, a consensus statement from exercise geneticists in the British Journal of Sports Medicine stated that "genetic tests have no role to play in talent identification or the individualized prescription of training to maximize performance." Similarly, the Academy of Nutrition and Dietetics stated that dietary advice based on genetics "is not ready for routine dietetics practice." Anecdotally, people also claim to have received confusing and sometimes conflicting interpretations from competing tests.

The same note of caution goes for blood-based analytics. "While athletes do have different needs, we don't have the evidence to say that if you're an athlete, your blood values should be in this range to achieve optimum performance," says Jamie Sheahan, director of nutrition at The Edge Sports & Fitness center in Vermont. "The science doesn't yet to tell us that these tests can be translated into performance or health-based outcomes."

Some blood biomarkers are transient, providing a snapshot in time and can fluctuate. "Even if a blood value comes back with a specific reading, it doesn't speak to how well your body utilizes that specific micronutrient," Sheahan says. Water-soluble vitamins like vitamin B12 may be elevated in your blood, but it may not be in the active form your body needs to use them.

What a test identifies as inflammation could be gone the next day. "If I have a huge marker for inflammation, does that mean I'm training hard and my body is recovering? Or does it mean there's an inherent problem? It's hard to distinguish that right now," Ormsbee says. And the average person, who may lack the expertise to interpret results on their own, could draw incorrect conclusions, he adds. "If you look at [higher inflammation] as a negative, you could actually hinder your performance by cutting back when it's not necessary based on a snapshot," Sheahan says.

Sheahan, in other words, encourages her clients to take this information with a grain of salt. While some companies have created user-friendly, easy-to-read reports and recommendations, she warns about adhering to the advice too strictly. "People can get so hyper-focused on micronutrients that they forget the bigger picture," she says. "They might omit other important things from their diet by replacing it with foods they're encouraged to consume to address deficiencies identified by the tests."

Which means if you're curious about your physiological and genetic makeup, these diagnostics can be a start. For some athletes, seeing personalized data and concrete numbers may kickstart a healthier diet and better training. "As long as you weren't duped into it and you have disposable income, it's fine if it helps you be more active," Sarzynski says.

But it's only one jumping-off point and not a magic bullet. No one biomarker or genetic marker will turn you into the next Serena Williams or Odell Beckham Jr. You'll still likely need to experiment with diet and exercise to find what actually works for you. Plus, data interpretations and methodologies will likely change as the fields of exercise science, nutrition, and genetics continue to evolve. Until there are consistent guidelines, these tests shouldn't be a replacement for your doctor or listening to your body.