For some it starts with the so-called Freshman 15; for others it may be the result of continuing to eat like an adolescent while adopting a more sedentary lifestyle as they grow older, but middle-age spread happens, and it cuts years from your life, suggests a new study.

The leading causes of preventable, premature death are heart disease, stroke, type 2 diabetes and some types of cancer, and all are related to obesity. Obesity is a national health crisis with nearly 40 percent of U.S. adults affected. It is defined as a body mass index (BMI) greater than 30 kg/m2. For example, a 5'3" woman who weighs 135 would have a BMI of 23.9.. A 6' 3" man weighing 250 would have a BMI of 31.2.

On a more positive note, being overweight (having a BMI less than 30, but higher than 25) had very little influence on the risk of premature death.

Over 36,000 people over the age of 40 were included in the study based on data collected during two U.S. National Health and Examination Surveys. Participants were weighed and measured at the beginning of the study. Researchers at the Huazhong University of Science and Technology in Wuhan, China asked people in the study to recall their weight 10 and 25 years earlier.

During the next 12 years, there were 10,500 deaths in the study population. Those whose BMI crossed the obesity line between young adulthood and midlife, or ages 25 to around 47, were 22 percent more likely to die prematurely and had a 49 percent greater risk of dying of heart disease. Being consistently obese had even worse results.

Though losing weight and moving from obese to nonobese during the same period of time was not associated with a risk of death, the same could not be said for people who lost weight later in life. People who lost weight between middle age and older adulthood had a 30 percent greater risk of dying early and a 48 percent greater risk of dying from heart disease.

The study found that remaining obese throughout adulthood, gaining weight between young adulthood and midlife, and losing weight between midlife and late adulthood were all associated with early death.

However, losing weight later in life may have been unintentional and the result of illness. Or perhaps people had constantly fluctuating weight throughout life, or perhaps they used unhealthy ways to lose weight, either of which could have increased their risk of premature death. More research is needed to better understand this finding.

On a more positive note, being overweight (having a BMI less than 30, but higher than 25) had very little influence on the risk of premature death, and no important relationship was found between weight change and death due to cancer in later adulthood.

Maintaining a normal weight throughout adulthood and, in particular, preventing weight gain during early adulthood may be important for the prevention of early death, the study found.

Losing weight once you are obese is very difficult and the success rate is low. Less than two percent of the people in the study lowered their BMI from obese to nonobese.

Efforts to bring attention to a preventing weight gain should get at least as much attention as the promotion of weight loss, not that weight loss isn’t beneficial as long as it is done through healthy and scientifically proven diet and lifestyle interventions.

The study is published in BMJ.