Being overweight is associated with a lot of health problems, and losing weight is often the best way to avoid them, no matter your age.
But this is not so simple, according to a study published Wednesday by BMJ, which examines the link between changes in body weight and the risk of premature death.
Researchers have found that the link between weight gain and mortality decreases with aging and weight loss in middle or late adulthood may increase the risk of premature death, especially when it comes to heart disease.
"It is our practice that it is best to prevent weight gain at a younger age in order to reduce the risk of premature death later in life," said study author An Pan, professor in the department in Epidemiology and Biostatistics at Tongji Medical College in Wuhan, China.
The study found that people who remained obese, measured by body mass index, had the highest risk of premature death throughout their adulthood. Weight gain from the mid-20s to middle age is also associated with an increased risk of mortality compared to people who remain of normal weight throughout their lives.
However, weight loss in middle and older age "is significantly associated with an increased risk of mortality.
Obesity is a major public health problem in the United States and globally. In the US, 38% of women and 36% of men were clinically obese in 2016, according to data cited by the study – 14% and 11% respectively in 1975.
Involuntarily by intentional weight loss  , which identified the study as limiting the study, Pan said the study did not include an analysis of the cause of later weight loss in life. One factor that may play a role is whether or not weight loss was intentional.
"Inadvertent weight loss can be a sign of underlying conditions such as diabetes or cancer," Pan said. Another reason, according to him, may be because weight loss involves someone who is already obese and thus already at a higher risk.
"The first message is to try not to gain weight when you are young and focus on maintaining a healthy lifestyle," Pan said. "Weight is of secondary importance."
The study found that people who are overweight but not obese throughout their adult life have little or no association with an increased risk of premature death.
The survey looked at 36,052 people aged 40 and over based on data from the US National Health and Nutrition Examination Survey – a nationally representative annual survey that included interviews, physical examinations and blood tests to assess the health of US citizens.
The weight of the participants was measured as part of the study and they were asked to share their weight from 10 years earlier and at 25 years of age.
Deaths from any cause, and in particular from heart disease, have been reported for an average of 12 years, during which time there were 10,500 deaths.
The study did not find a significant relationship between different patterns of weight change and cancer deaths.
Previous studies have linked high BMI in adulthood with higher rates of premature death, but much less is known about the role of weight change over time. Pan said more research is needed to unravel the causes of the link between changes in body weight and mortality and the long-term health effects of weight loss.