The odds are against obese men and women trying to get to a healthy weight, particularly if they are severely obese, a U.K. study suggests.
Researchers followed 76,704 obese men and 99,791 obese women for up to nine years. In any given year during the study, the probability that a patient might achieve a normal body weight was 1 in 210 for men and 1 in 124 for women.
For those who were severely obese, the annual odds stretched to 1 in 1,290 for men and 1 in 677 for women.
"The findings are not entirely unexpected as the weight trajectory for most is a gradual increase until late middle age," said senior study author Martin Gulliford, a primary care and public health researcher at King's College London. "Large reductions in body weight tend to be unusual."
Globally, 1.9 billion adults are overweight or obese, according to the World Health Organization. Obesity increases the risk of heart disease, diabetes, joint disorders and certain cancers.
Previous research has found obese people often struggle to shed excess pounds or keep weight off when they do lose it. Lifestyle changes such as following a healthy diet and getting regular exercise can often help in the short-term but fail to produce lasting results, particularly among people who have more than 100 pounds to lose before reaching a healthy weight.
For the current study, Gulliford and colleagues focused on whether obese people who didn't get weight loss surgery could reach a healthy weight, as well as whether they could successfully shed just 5 percent of their weight.
"Reductions of body weight of 5 percent or more are very valuable as this will reduce the harmful metabolic effects of excess weight," Gulliford said by email.
Researchers analyzed data on obese people aged 20 years and older from a national database in the U.K. from 2004 to 2014.
To be included in the study, participants had to have at least three records of their body mass index (BMI), a measure of weight relative to height, in the database so researchers could estimate changes over time.
A BMI between 18.5 and 24.9 is considered a healthy weight, 25 to 29.9 is overweight, 30 or above is obese and 40 or higher is what's known as morbidly obese.
An adult who is 5’ 9” tall and weighs from 125 to 168 pounds would have a healthy weight and a BMI of 18.5 to 24.9, according to the U.S. Centers for Disease Control and Prevention. An obese adult at that height would weigh at least 203 pounds and have a BMI of 30 or more.
At the start of the study, the men were 55 years old on average and the women were 49.
After a maximum of nine years, just 1,283 men and 2,245 women achieved a normal weight.
Overall, the annual likelihood of losing 5 percent of body weight was 1 in 12 for men and 1 in 10 for women, the researchers estimated. For people who were morbidly obese at the start of the study, the odds of achieving this milestone improved – narrowing to 1 in 8 for men and 1 in 7 for women.
It's possible that these estimates might be thrown off by inaccurate data on height or weight for the study participants, the researchers acknowledge in the American Journal of Public Health.
Even so, the findings highlight the benefit of focusing on diet and exercise changes that may be needed to achieve that first 5 percent weight loss, which can often be achieved within six months, said Marion J Franz, of Nutrition Concepts by Franz in Minneapolis.
"Research has shown important health benefits from a weight loss of about 5 percent – prevention or delay of type 2 diabetes, decreases in blood pressure, decreases in circulating inflammatory markers, and potential improvements in lipids," Franz, who wasn't involved in the study, said by email.
"Therefore, weight loss interventions should promote health benefits not achieving an ideal body weight," she said.