Gaining weight in your 20s, 30s and early 40s increases your early death risk by more than a fifth.
This is according to a newly-released study, published in the British Medical Journal (BMJ)
Specifically, becoming obese between the ages of 25 and 47 increased your risk of dying from any cause by 22%.
Risk of dying from heart disease – a condition often linked to obesity – also increased by 49%.
However, adults could counteract their early death risk through losing the weight during the same time period.
Reversing early death risk through weight loss
Those who went from being obese to being a healthy weight between the ages of 25 and 47 had no increased death risk compared to those who sustained a healthy weight during this period.
Yet those who lost weight when they were older did not appreciate the same benefit, according to the study.
Those who went from being obese to a healthy weight between middle age and later in life had a 30% increased risk of dying early from any cause and a 48% increased risk from heart disease, researchers found.
For the study, experts analysed data for 36,051 people aged 40 or over at the start of the study. The study was conducted on US citizens and was led by a team from the School of Public Health at Huazhong University of Science and Technology in China.
Each participant was weighed and measured at the start. They told researchers their weight when they were 25, and also 10 years previous to the study (on average, this meant at the age of 47).
Experts followed the group for 12 years, during which time 10,500 deaths were recorded.
Overall, being obese for the entirety of adult life still carried the biggest risks - with up to a 72% increased danger of dying young, it was found.
Importance of maintaining ‘normal weight’
"Stable obesity across adulthood, weight gain from young to middle adulthood, and weight loss from middle to late adulthood were associated with increased risks of mortality,” concluded authors in the report.
"The findings imply that maintaining normal weight across adulthood, especially preventing weight gain in early adulthood, is important for preventing premature deaths in later life."
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Tam Fry, spokesman for the UK’s National Obesity Forum, said: "The message to maintain a healthy weight throughout life couldn't be clearer.
"Some 12 years ago the well-respected Foresight Report first stunned the UK by predicting that being fat could knock 13 years off your life.
"But given the continuing rise of obesity-related hospital admissions, few people appear to have listened."