Gaining weight young: consequences for life

It has long been known that obesity increases the risk of many diseases. But one question is less studied: does the time of life when we gain weight play a role? This is what researchers from Lund University (Sweden) sought to understand, based on a vast database.

Their results, published in April 2026 in the journal eClinicalMedicineshow that early weight gain can have repercussions decades later.

When you gain weight matters as much as the kilos

The study is based on data from more than 620,000 people, followed for an average of 23 years for men and 12 years for women. To be included, participants had to have at least three weight measurements between the ages of 17 and 60. The strength of this study lies in the quality of the measurements because the majority of the data were collected by health professionals in medical contexts.

On average, men and women gained 0.4 kg per year during adult life. But analysis shows that the earlier weight gain occurs, the higher the risk of dying prematurely.

People whose obesity set in between the ages of 17 and 29 show a approximately 70% higher risk of premature death than those who did not develop obesity before age 60.

Even moderate weight gain is important: gaining 0.5 kg per year between the ages of 17 and 30, or around 6.5 kg over this period, is associated with a 17% higher risk of premature death, compared to those whose weight has remained stable.

“A possible explanation why people whose obesity begins early are at greater risk is their longer exposure to the biological effects of excess weight,” suggests in a press release Huyen Le, doctoral student at Lund University.

An exception: cancer in women

In the Swedish study, the general picture has one exception. In women, the risk of dying from obesity-related cancer was similar regardless of the time of weight gain, suggesting that other biological mechanisms come into play. The researchers cite hormonal changes linked to menopause, which could interfere with the direct link between age of weight gain and cancer risk.

Why obesity leaves a mark even after weight loss

A study published at the end of April 2026 in the journal EMBO Reports sheds biological light on this phenomenon. Researchers at the University of Birmingham (UK) have shown that obesity imprints a lasting “memory” in immune cells, even after the person has lost weight.

The mechanism involved is that of DNA methylation: during the period of obesity, chemical marks (“tags”) are attached to the DNA of certain lymphocytes. These marks modify the functioning of these cells, in particular their ability to eliminate cellular waste (autophagy) and the aging of the immune system. However, these epigenetic marks persist long after weight loss. According to researchers’ estimates, it would take 5 to 10 years of maintaining a normal weight for this “immune memory of obesity” to gradually fade.

“Our results show that obesity is associated with lasting epigenetic modifications that influence the behavior of immune cells. The immune system thus retains a molecular trace of past metabolic exposures, which may have implications for long-term disease risk. explains Dr. Belinda Nedjai, co-author of this study, in a press release.

These results partly explain why people who have lost weight remain exposed to certain obesity-related risks, such as type 2 diabetes and certain cancers, even several years after having regained a normal weight. Weight loss is of course beneficial, but it does not immediately erase the accumulated biological effects.

“We know that obesity is a chronic, progressive and relapsing disease. Our results allow us to better understand the molecular mechanisms that can promote relapses,” adds Professor Andy Hogan, from Maynooth University.

What to remember

Taken together, these two studies send the same message: preventing obesity early in adult life is not just a matter of immediate well-being. It is a long-term investment in health, because the accumulated pounds leave a lasting biological trace that weight loss alone is not enough to quickly erase.

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