A large-scale study tracking hundreds of thousands of individuals reveals that the timing of weight gain may play a critical role in long-term health.
When people gain weight during life can shape their health decades later. In a study of more than 600,000 individuals, researchers at Lund University in Sweden examined how weight changes between ages 17 and 60 relate to the risk of death from various diseases. The findings point to a clear trend: weight gain in early adulthood appears to have the strongest long-term effects.
Obesity has long been linked to a higher risk of many diseases. This study shifts the focus by exploring how weight changes across adulthood, rather than weight at a single point, influence health outcomes.
“The most consistent finding is that weight gain at a younger age is linked to a higher risk of premature death later in life, compared with people who gain less weight,” says Tanja Stocks, Associate Professor of Epidemiology at Lund University. She is one of the researchers behind the study, which has now been published in eClinicalMedicine.
The analysis draws on data from more than 600,000 people tracked through national records. To be included, participants needed at least three recorded weight measurements, such as during early pregnancy, at military conscription, or in research settings. Over the study period, 86,673 men and 29,076 women died.
Early Weight Gain Carries Higher Risk
Researchers examined how body weight changed from ages 17 to 60 and how these changes related to overall mortality and deaths linked to obesity-related diseases (see fact box). On average, both men and women gained about 0.4 kilograms per year (about 0.9 pounds per year).
Those who gained weight more quickly during adulthood faced a higher risk of death from the diseases studied. People who first developed obesity between ages 17 and 29 had about a 70 percent higher risk of premature death compared with those who did not develop obesity before age 60. Obesity onset was defined as the first time a person’s body mass index, a measure based on weight and height (kg/m²), reached 30 or higher.
“One possible explanation for why people with early obesity onset are at greater risk is their longer period exposed to the biological effects of excess weight,” says Huyen Le, a doctoral student at Lund University and the study’s first author.
However, one exception stood out in the results: cancer risk in women.
“The risk was roughly the same regardless of when the weight gain occurred. If long-term exposure to obesity were the underlying risk factor, earlier weight gain should imply a higher risk. The fact that this is not the case suggests that other biological mechanisms may also play a role in cancer risk and survival in women,” says Huyen Le.
One possible explanation involves hormonal shifts linked to menopause.
“If our findings among women reflect what happens during menopause, the question is which came first: the chicken or the egg? It may be that hormonal changes affect weight and the age and duration over which these changes occur – and that weight simply reflects what’s happening in the body.”
Strong Data and Reliable Measurements
A key strength of the study is its use of repeated weight measurements for each participant, allowing researchers to track changes over decades. Many previous studies rely on people recalling their past weight, which can be less accurate.
“The majority of weight measurements in this study were, instead, taken by staff, for example in healthcare settings. The predominance of objectively measured weights in our study contributes to more reliable and robust results,” says Tanja Stocks.
Population-level risk increases can be hard to interpret. For instance, a 70 percent increase in risk means that if 10 out of 1,000 people in a reference group die during a certain period, about 17 out of 1,000 would die among those with early obesity.
“But we shouldn’t get too hung up on exact risk figures. They are rarely entirely accurate, as they are influenced, for example, by the factors taken into account in the study and the accuracy with which both risk factors and outcomes have been measured. However, it’s important to recognize the patterns, and this study sends an important message to decision-makers and politicians regarding the importance of preventing obesity,” says Tanja Stocks.
Many researchers describe today’s environment as an “obesogenic society,” where surroundings make healthy choices more difficult and encourage weight gain.
“It’s up to policymakers to implement measures that we know are effective in combating obesity. This study provides further evidence that such measures are likely to have a positive impact on people’s health.”
Reference: “Weight trajectories and obesity onset between 17 and 60 years of age, and cause-specific mortality: the Obesity and Disease Development Sweden (ODDS) pooled cohort study” by Huyen T. Le, Marisa da Silva, Louise Bennet, Ahmed Elhakeem, Christel Häggström, Ming Sun, Innocent B. Mboya, Jens Wahlström, Karl Michaëlsson, Sven Sandin, Patrik K.E. Magnusson, Ylva Trolle Lagerros, Abbas Chabok, Lena Lönnberg, Sölve Elmståhl, Karolin Isaksson, Sara Hägg, Bright I. Nwaru, Hannu Kankaanranta, Linnea Hedman, Anton Nilsson, Josef Fritz and Tanja Stocks, 10 April 2026, eClinicalMedicine.
DOI: 10.1016/j.eclinm.2026.103870
Funding: The Swedish Research Council, Swedish Cancer Society, Crafoord Foundation, Malmö General Hospital Cancer Foundation, The Swedish Foundation for Strategic Research
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