Millions of people in the United States alone have submitted their DNA for analysis and received information that not only predicts their risk for disease but, it turns out, in some cases might also have influenced that risk, according to a recent study by researchers at Stanford University.

The team, led by Alia Crum, assistant professor of psychology, found that when people were told of a genetic propensity for either obesity or lower exercise capacity, it altered the way their bodies responded either to a meal or to exercise. The work was published Dec. 10 in Nature Human Behavior.

"Receiving genetic information doesn't just make you more informed," Crum said. "What this study shows is that it can also have a physiological impact on your body in a way that actually changes your overall risk profile."

Crum and the study's lead author, graduate student Bradley Turnwald, said that the results don't suggest that DNA testing is bad or good, just that when delivering information, genetic counselors or personalized genetic testing companies need to be aware that the mere knowledge of the test result could influence a person's risk.

A brief deceit

To carry out the research, the group first took DNA samples from people who were told they were participating in a study about the relationship between DNA and diet. Later, the participants returned and 116 of them carried out an exercise test, while 107 of them ate a meal. After the meal, the researchers measured levels of molecules in the blood that indicate hunger or fullness.

Unbeknownst to the participants, Crum and Turnwald had tested the participants for one of two genes – one that has been associated with obesity and one associated with exercise capacity. During that first round of tests, the researchers could see small differences in either exercise capacity or satisfaction after the meal, depending on which version of the gene the people carried.

Keep the benefits, eliminate the risk

Immediately after the testing, Crum and Turnwald told participants about the research goals and revealed their actual genetic risk if the participant still desired. "We took a lot of steps to conduct the research ethically and ensure participants' safety," Turnwald said.

"For example, we chose genes related to obesity and exercise capacity because we knew that information would be meaningful but less emotionally charged than genes related to diseases like cancer, and participants only held a potentially false belief about their genetic risk for one hour while under our supervision before being fully debriefed."

Next, the researchers are interested in exploring whether there are ways to explain the genetic risk that eliminate the effects they saw in this study. "How can you deliver genetic information in a way that has the beneficial effects in terms of motivating people to change their behavior but that doesn't provoke a negative effect on physiology, emotions, and motivation? That's where I think a lot of really good work can be done," Crum said.