A study has found that people whose weight reduced from indicating obesity to indicating overweight between early adulthood and midlife had a halved risk of dying during the follow-up period.

The World Health Organization (WHO) estimate that the global prevalence of obesity has almost tripled since 1975. In 2016, more 650 million adults had obesity.

In the United States, the prevalence of obesity among adults increased from 30.5% to 42.4% of the population between 1999 and 2018, according to the Centers for Disease Control and Prevention (CDC).

Obesity is associated with an increased risk of heart disease, stroke, type 2 diabetes, and some types of cancer, making it a major cause of preventable premature death.

Estimates of the number of deaths that can be attributed to obesity vary widely, however, because of the complex interactions between body weight and factors such as age, smoking, diet, and physical exercise.

In addition, scientists are still unsure whether carrying excess weight in young adulthood causes harmful physiological changes that cannot be reversed by subsequent weight loss.

A team led by researchers at the Boston University School of Public Health, in Massachusetts, set out to discover whether losing weight after having obesity in early adulthood is associated with a reduction in mortality risk later in life.

Doctors often use a measure called body mass index (BMI) to determine whether a person has a healthy weight. To calculate this, the doctor divides the person’s weight in kilograms by their height in meters squared.

Experts define a healthy BMI as 18.5–24.9, one indicating overweight as 25.0–29.9, and one indicating obesity as 30 or higher.

The researchers behind the present analysis analyzed data from 24,205 people in the U.S. who were part of the National Health and Nutrition Examination Survey (NHANES).

The team found that going from a BMI indicating obesity in young adulthood to one indicating overweight by midlife was associated with a 54% reduction in mortality risk, compared with maintaining a BMI of obesity over the same period.

Also, people who shifted from having obesity to overweight between young adulthood and midlife had much the same mortality risk as people who had overweight only during this period.

The scientists estimate that 3.2% of all the early deaths in the study would have been prevented if people with BMIs indicating obesity had reduced this measure to fall within the overweight range by midlife.

In addition, they calculate that 12.4% of all the early deaths could have been avoided if everyone with a BMI indicating overweight or obesity had reduced it to fall within the healthy range by middle age.

“The results indicate an important opportunity to improve population health through primary and secondary prevention of obesity, particularly at younger ages,” says senior study author Prof. Andrew Stokes.

Another study author, Dr. JoAnn Manson, chief of preventive medicine at Brigham and Women’s Hospital, in Boston, refers to the link between obesity and a range of chronic illnesses:

“Although this study focused on preventing premature deaths, maintaining a healthy weight will also reduce the burden of many chronic diseases, such as hypertension, diabetes, heart disease, and even cancer,” she says.

Reflecting the public health challenge posed by overweight and obesity, however, the study found that weight loss was rare among the participants.

“The discrepancy likely reflects the different nature of weight loss at an earlier versus later life course. Weight loss at an older age is often unintentional, associated with underlying health conditions, and/or age-related loss of muscle mass, whereas weight loss earlier in life tends to capture changes in fat mass and is less likely to be affected by the onset of chronic diseases.”

Medical reference: Medical News Today