The chances of a person achieving normal body weight again after becoming obese are very low, new research suggests.
For those who did manage 5% weight loss, more than half (53%) regained it within two years and nearly four in five (78%) put it on again within five years.
The health study, which was led by King's College London, found the chance of an obese person attaining normal body weight was just one in 210 for men and one in 124 for women, while it was just one in 1,290 for men and one in 677 for women with severe obesity.
The findings, published in the American Journal of Public Health, suggest that current weight-management programmes focused on dieting and exercise are failing to achieve sustained weight loss for the majority of obese patients.
Researchers tracked the weight of 279,000 men and women using UK health records from 2004 to 2014. A minimum of three body mass index (BMI) records per patient was used to estimate weight changes and anyone who received bariatric surgery was excluded from the study.
Overall, only 1,283 men and 2,245 women with a BMI of 30-35 (considered obese) reached their normal body weight. Those with a BMI above 40 were classed as severely obese.
"Weight cycling", with both increases and decreases in body weight, was also observed in more than a third of patients.
Dr Alison Fildes, of the Division of Health and Social Care Research at King's College London, said: "Losing 5% to 10% of your body weight has been shown to have meaningful health benefits and is often recommended as a weight-loss target. These findings highlight how difficult it is for people with obesity to achieve and maintain even small amounts of weight loss.
"The main treatment options offered to obese patients in the UK are weight-management programmes accessed via their GP. This evidence suggests the current system is not working for the vast majority of obese patients.
"Once an adult becomes obese, it is very unlikely that they will return to a healthy body weight.
"New approaches are urgently needed to deal with this issue. Obesity treatments should focus on preventing overweight and obese patients gaining further weight, while also helping those that do lose weight to keep it off. More importantly, priority needs to be placed on preventing weight gain in the first place."