Is DNA destiny? How your mind and body might process health-related information

We've all been told we inherit traits from our families — "You run slow, just like your father," "You have your mother's small appetite" — and hearing such beliefs in childhood can have an undeniably profound and lasting impact. But even as adults, assertions about our health "destiny" can loom large.

This is especially true with the rise of genetic testing. Direct-to-consumer DNA kits are a steadily growing industry, and now offer more than just the opportunity to uncover your ancestry. New fitness-geared tests claim to tell you everything from your ideal DNA diet to the best workout to try according to your genetic strengths and weaknesses.

But we may be underestimating just how much influence this kind of information can have on us. As a new study suggests, learning about our genetic predispositions can cause a significant change in our exercise performance and even our body chemistry — whether the information is true or not.

Just how suggestible are we?

In the study, published by researchers at Stanford University, participants had their DNA tested for genes related to exercise capacity and obesity. Next, one group was asked to perform an exercise test to measure their cardiorespiratory capacity, while another group took an eating test to measure their level of fullness.

A week later, participants were randomly given the "results" of their DNA tests: some were told they had a genetic predisposition for a higher or lower exercise capacity, and some were told they had a genetic inclination for or against obesity — whether they actually carried these genes or not. They were then asked to retake the same exercise and eating tests.

After the second round, researchers discovered that simply learning the genetic information noticeably changed participants' performances. People who were told they had a lower exercise capacity actually performed the exercise test as if they were in worse shape, registering lower lung capacity and quitting earlier, while participants who were told that they had a genetically lower risk of obesity actually produced more than double the amount of the fullness hormone than before.

In short, being told that they had a genetically higher risk for low exercise capacity or obesity made participants perform worse and eat more than those who were told they had the protective gene, whether they actually had these genes or not. It all speaks to the very real power of belief on the body.

"The take-home message here is that the mindset that you put people in when you deliver genetic risk information is not irrelevant," said assistant professor of psychology Alia Crum, who led the study. "The mindset of being genetically at risk or protected can alter how we feel, what we do and — as this study shows — how our bodies respond."

The role of authority

Family doctor and health writer, Dr. Melissa Lem, did not find the results of the study surprising. "The placebo effect is a well-known phenomenon among the medical community, and every day I see patients whose beliefs and attitudes play a major part in their symptoms and health status."

Dr. Lem takes great care in being compassionate and patient-centred when discussing any issue with her patients, including when they come to her with weight or fitness concerns. "I'm happy that they trust me enough to seek my opinion on these sensitive topics," she says. And such consideration can go a long way. Usually, learning about risks motivates her patients to make healthy changes, she says, rather than becoming a self-fulfilling prophecy.

Of course, beyond the realm of medicine, the influence of authority still exists. Dr. Lem believes a responsibility of care should extend to anyone in a potentially influential position, including parents, teachers, "experts" and celebrities. "I think everyone should strive to be as accurate and evidence-based as possible when expressing their opinions and ideas," she says. "They should take responsibility for what they put out there, because it can affect many in possibly negative ways."

"The thing is, we are all suggestible when presented with the right kind of evidence from the right kind of authority," explains Dr. Norman Farb, an assistant professor of psychology at the University of Toronto whose research focuses on the neuroscience of human identity and emotion. Psychological influence from authority can impact our physical health just as our own strongly held beliefs can directly affect our bodies. "How many of us have forestalled an illness knowing it was unacceptable to be sick given our professional or familial commitments, only to be hit hard by the illness when the responsibility passes?"

"I think that we are just scraping the surface of how strongly our expectations structure our realities, not just in terms of beliefs and thoughts, but also in terms of our physiology and behaviour."

Buyer beware

As much as experts and influential individuals should take care when it comes to the messages they're sending, we need to be critical of how we're receiving and internalizing them, too. This is true when it comes to re-evaluating messaging from our childhood, as well as the results from direct-to-consumer DNA testing, which has mixed credibility at best.

Holes have already been poked in some at-home ancestry testing kits (one geneticist from FamilyTreeDNA admitted to it being "kind of a science and an art"), while nutrition- and fitness-geared genetic testing has similarly been spotty in its results. A 2018 Stanford University study found that participants lost a yearly average of 13 pounds on different diets, regardless of their genes.

"I don't think the evidence is there yet for the benefit of direct-to-consumer DNA tests," says Dr. Lem. "When physicians order DNA tests, they're typically used to diagnose conditions that come down to specific mutations, and give a yes or no answer about the presence of a certain disease. That's not the case with fitness-focused tests, which deal in probabilities of certain health conditions or tendencies, which are usually low."

The Canadian Medical Association also warns that direct-to-consumer genetic testing isn't regulated in Canada and companies don't not have to back their claims with clinical results, so a degree of caution and skepticism should be exercised.

Information as motivation

Skepticism is useful when dealing with what at-home tests or what our parents told us, but when your doctor informs you of a genetic risk (like a family history of heart disease) or relays the results of a medically administered DNA test, it should be taken seriously.

"What we have to remember is that interpreting genetic testing results is a numbers game," says Dr. Lem. "Even if having a certain gene mutation increases your chances of having a certain disease or condition by 20 per cent, it's still much more likely that you won't be affected."

Furthermore, those risks can often be lessened with adherence to healthy living. "In many cases, lifestyle choices and environment play a much more significant role in health outcomes," Dr. Lem explains. "So avoid focusing on things you can't change, like your genes, and pay attention to what you can improve, like your diet, exercise and sleep habits."

"Even if we can't [totally] overcome the negative expectation handed down from an authority, knowing that all of our worldview is made up by a tapestry of expectations, and focusing on the ones we can do something about, this is where empowerment and motivation can come from," agrees Dr. Farb.

That goes for your fitness level, too. It won't "help you alter the laws of physics," he continues. "But can you push past warning signals of fatigue in your body, or conversely become more sensitive to existing feelings of satiety after a meal? Of course!"

Food for thought

As we take in pieces of information on how to live our healthiest lives, it's paramount to be aware of how internalizing them can negatively affect our behaviours and bodies, no matter how true they may be. We're all going to encounter such information — positive and negative, credible and questionable — but doubling down on healthy, active living regardless appears to be the best way to maximize your health outcomes.  

"Noticing what the dominant expectations that fill our minds are, and trying to cultivate realistic, positive and empowering expectations is critical, rather than letting this garden of expectancy be filled with weeds," says Dr. Farb. "There are so many things a person can do and find meaningful improvement, once they decide they want to improve and not focus on negative prophecies."

Have you ever internalized any ideas about your fitness potential or health destiny? Do they still affect you today, or have you fought to overcome them?