Losing weight is often framed as the hard part. Keeping it off can be even harder, and new research suggests that challenge may not look the same for everyone.
A study published in Obesity found that postmenopausal women with a higher genetic risk for obesity regained weight about twice as fast as those with lower genetic risk, even though both groups lost similar amounts of weight to start.
“Obesity is stigmatized and often associated with laziness,” said Harold Lee, assistant professor of biobehavioral health at Penn State. “That is a stubborn myth.”
The findings point to one way biology may influence what happens after weight loss, not just during it.
The researchers analyzed data from nearly 10,000 women ages 50 to 79 who participated in the long-running Women’s Health Initiative Dietary Modification trial. During the first year, participants followed a low-fat diet and met regularly with a dietitian. On average, they lost about four pounds, regardless of their genetic risk.
The differences showed up over time. In the years that followed, most participants regained weight. Among white women, those with the highest genetic risk regained weight at about twice the rate, roughly two pounds per year compared to about one pound per year among those with lower genetic risk.
“Maintaining weight loss is very difficult, and most women regained weight,” Lee said. “Unexpectedly, white women with high genetic risk regained the weight much faster, which could make maintaining a healthy weight even more difficult.”
Genetic risk was measured using a polygenic risk score, which combines information from many genes to estimate a person’s likelihood of developing a condition such as obesity. In this study, women in the top 5% of scores were classified as having high genetic risk.
Notably, genetic risk did not appear to affect whether participants lost weight in the first place. All groups saw similar initial results during the structured diet and counseling period.
“The United States has experienced an obesity epidemic over the past several decades,” Lee said. “This was not due to changes in human genetics. What changed, rather, was the environment around us.”
That environment, he explained, can make weight maintenance more difficult, especially for those who are more biologically susceptible. At the same time, the structured support in the study showed that behavior and environment can still play a meaningful role.
“In this study, we saw a clear effect of genetic risk in how quickly women regained weight,” Lee said. “On the other hand, genetic risk did not influence weight loss.”
The findings also highlight limitations in how genetic risk is measured. The polygenic risk score used in the study predicted weight regain in white women but not in Black women, likely because the genetic data used to build the score has historically included fewer non-white participants.
“Because fewer Black people were involved in the creation of the risk score, it does not represent them as accurately,” Lee said. “We need to find ways to include more people of color in large scale genetic studies.”
The study was observational, meaning it cannot prove that genetic risk directly caused faster weight regain. The amount of weight lost in the study was also modest, which may affect how broadly the results apply.
Still, the findings offer a clearer explanation for why maintaining weight loss can feel more difficult for some people than others. Genetics may not determine whether weight loss is possible, but they may influence how hard it is to hold onto those changes over time.
This study was funded by the National Institutes of Health’s National Heart, Lung, and Blood Institute.