The sales pitch is compelling: By revealing the secrets locked inside your DNA, genetic testing can optimize your workout gains while reducing your risk for injury. “Remove the guesswork from training,” claims one company. “Take your exercise choices to the next level,” says another.

The companies selling these services (often for hundreds of dollars) say they’re backed by hard science. But take a close look at the research undergirding these products and you’ll catch a distinct whiff of snake oil.

“There are some companies out there who are just making stuff up or exaggerating to the point of fraud, but even the companies that aren’t making fraudulent claims are utilizing the scientific aura surrounding DNA to imply that there’s more evidence than there really is,” says Robert Green, MD, a professor of medicine at Harvard Medical School and director of the Genomes2People Research Program based at Brigham and Women’s Hospital.

Green says there are some genetic markers associated with the activity of fast twitch muscle fibers. These genes may play a minor role in a person’s response to different types of resistance training. Using this kernel of genetic science as a foundation, companies are constructing whole training programs that are purportedly tailored to a person’s unique genetic blueprint.

But Green says the genetic markers these testing companies look at are only single pieces of a very complicated puzzle. How (and how much) they matter remains to be seen and probably depends on hundreds of other variables. “It’s very easy for these companies to misrepresent the connection between your DNA and your desired outcome,” Green says.

Others agree. When it comes to fitness-focused genetic testing, “These products are going out on a limb in terms of interpretation of the science,” says Jason Vassy, MD, a genetic science researcher and assistant professor of medicine at Harvard.

“There are some companies out there who are just making stuff up or exaggerating to the point of fraud.”

Vassy points out that even if a person carries a genetic mutation linked to an elevated risk for a disease, simply having the gene mutation is no guarantee that the person will actually develop the associated disease. Likewise, someone who carries a genetic variable associated with a particular response to training is not guaranteed to have that response. In fact, they may have the opposite response, Vassy says.

When it comes to the interplay between a person’s genes and workouts, “We know genetics is important, but we mostly don’t know which specific genetic variations are [important],” says Alun Williams, a researcher in sport and exercise genomics at Manchester Metropolitan University in the U.K. “The companies that sell genetic tests to the average consumer don’t tell their customers that.”

In 2015, Williams co-wrote a consensus statement — basically, an expert opinion based on a review of the existing scientific literature — on fitness genetic testing. He and his co-authors stated that genetic testing has “no role to play in… the individualized prescription of training to maximize performance.” His opinion hasn’t changed. “There are some promising findings,” Williams says, but what we know today is “a tiny fraction” of the whole.

Some of the big companies selling fitness genetic testing acknowledge these issues — though you have to dig pretty hard to find those disclosures.

For example, DNAFit has a research page on its website that links to a BMJ editorial co-authored by the company’s own head of sports science. That editorial talks about the “potential” of recent advances in genetic science to help elite athletes make training decisions. But the usefulness of these new discoveries “remains highly controversial,” the editorial states. “It seems wise to proceed cautiously, skeptically, but with an open mind.”

The flip side of all this is that none of these companies — at least none of the most prominent ones, like DNAFit and Fitness Genes — are selling fitness information that is likely to do you harm. Exercise is inherently healthy; doing a little more of one type instead of another isn’t going to hurt you. Also, some of the most well-established companies — again, DNAFit is a good example — bundle their testing services with access to fitness coaches and other helpful resources, so you’re still getting some bang for your buck.

Finally, it’s worth noting that many people find it hard to get motivated to exercise. There’s evidence that genetic testing can motivate people to work out or adopt other healthy behaviors. Learning about your own genes seems to make the benefits of a healthy lifestyle “more real” to people, Green says.

The claims many of these testing companies make are misleading, and there is scant evidence tying genetic markers to training outcomes. But if you have money to burn and understand the shortcomings of these tests, you may still find them entertaining — and maybe even a little inspiring.