The unhealthy lifestyle behaviors that may underlie the notorious “freshman 15,” — ie, weight gain that some students may experience in starting college, often persist well into adulthood and are linked to a greater likelihood of having increases in BMI levels in early adulthood compared with those who have healthy lifestyle habits early on, new research showed.

“This study represents one of the first longitudinal investigations into the associations between lifestyle behavior trajectories and weight patterns from precollege to adulthood,” reported the authors in the study, published in January in Nutrients.

“Our findings highlight how important it is to build healthy behavior patterns before young people enter college and to maintain those patterns as they move into adulthood,” senior author Daniel P. Hatfield, PhD, an adjunct assistant professor at the Gerald J. and Dorothy R. Friedman School of Nutrition Science and Policy at Tufts University, Boston, told Medscape Medical News.

The study, following a population from college years up to 20 years later found that “precollege lifestyle behaviors are often maintained into adulthood, and those maintaining healthy lifestyle behaviors or improving lifestyle behaviors were more likely to sustain a healthy weight, while those with persistently poor behaviors experienced greater weight gain.”

Previous research shows that the most significant weight gain takes place during emerging adulthood, or between the ages of 18-25, research has been lacking on the lifestyle habits associated with that weight gain — and what their long-term implications are.

To further investigate, Hatfield and his colleagues evaluated data from health surveys of 4783 incoming undergraduate students at the school completed between 1998 and 2007, and from follow-up surveys from 970 of those same students conducted in 2018, representing time spans of 11 to up to 20 years.

The surveys inquired about demographic variables and lifestyle behaviors, including diet, physical activity, sleep, height, and weight.

Based on the responses, the participants were categorized into five lifestyle patterns: stable healthy, stable moderately healthy, stable minimally healthy, worsened, or improved.

Their BMI patterns were also categorized based on five weight status definitions. About 60.3% of responses analyzed were women, 77.9% were non-Hispanic White individuals, and their precollege mean age was 17.8 years.

The most common combined lifestyle pattern between precollege and adulthood was “stable moderately healthy,” observed in 36.7% of responders.

Overall, about half (49.7%) of the participants remained in the same lifestyle pattern category from precollege age into adulthood, “suggesting that many people’s behaviors are fairly stable from precollege to later adulthood,” Hatfield said.

Of those who did change lifestyles, 31.7% transitioned to a less healthy pattern, while only 18.6% transitioned to a healthier pattern.

Weight Changes Over Time

In terms of weight changes, the proportion of respondents in the normal weight category declined from 86% in precollege years to just 67% in adulthood.

Notably, the prevalence of respondents who had overweight, though much smaller, more than doubled over the study period, from 12% to 25%, while rates of obesity quadrupled, from 2% to 8%.

Only 0.7% of participants moved to a healthier weight category during the study period, however, with 86% already in a healthy weight range at baseline, “there was limited room for improvement,” Hatfield noted.

The mean weight gain (kg and BMI) was the most pronounced among respondents with a stable, but minimally healthy lifestyle (17.8 lb [1.19 lb/year], 2.9 BMI units), with that category characterized by lower engagement in healthy lifestyle or dietary behaviors, less physical activity, and poorer sleep.

Meanwhile, those maintaining a stable healthy lifestyle experienced the least amount of weight gain (8.8 lb [0.55 lb/year], 1.4 BMI units).

Of note, the average weight gain from the precollege to alumni time points was greater among men than among women, by about 6 lb.

Overall, “among those who began with overweight or obesity, relatively few moved to a healthier category,” Hatfield added.

“This aligns with a substantial body of research showing that excess weight in adolescence often persists into adulthood.”

Effect of GLP-1s?

With a cutoff of 2018, a key question is how weight trajectories over time may be currently changing as a result of the advent of GLP-1s, which have transformed the weight loss landscape.

According to one recent KFF poll, 10% of adults aged 18-29 years reported having ever used GLP-1s as of November 2025, and that rate is only expected to rise.

However, though representing an important tool, with costs and high discontinuation rates common with GLP-1s, “they’re just one part of the solution,” Hatfield noted.

“We also need broader policy, systems, and environmental strategies that make healthy behaviors easier, more accessible, and more sustainable for everyone,” he said.

From Campuses to Clinicians — Both Can Have Key Roles

Importantly, the communal culture of a college campus lends itself to the promotion of healthier lifestyle choices, through a variety of outreach measures.

“Colleges and universities are uniquely positioned for promoting sustainable, healthy behaviors,” the authors asserted.

Hatfield added that, specifically, measures “could include improving the nutritional quality of dining options, enhancing walkability and bike-ability, or other strategies that help ensure that healthy behaviors aren’t just encouraged but also feasible.”

Meanwhile, before even arriving at college, physician encounters can lay the groundwork for informed choices.

“Clinicians play a key role here: their guidance can meaningfully influence patients’ habits around nutrition, physical activity, and sleep,” he said. “At the same time, it’s essential that these conversations are delivered in a supportive, nonstigmatizing way.”

“We know from extensive research that weight‑based stigma in healthcare can undermine patient trust, discourage care‑seeking, and negatively affect health behaviors,” Hatfield added.

“Approaching these discussions with empathy and respect helps ensure that recommendations benefit patients’ long‑term well‑being.”

On a broader level, promoting healthy weight requires coordinated efforts, including “policy, systems, and environmental approaches that make healthy choices easier and more accessible for everyone,” Hatfield added.

The authors had no disclosures to report.