The risk of developing dangerous obesity-related complications such as type 2 diabetes and cancer may not fully disappear after losing weight, a study has found.
Researchers have found that obesity causes a ‘tagging’ process on immune cells – which protect the body against bacteria, viruses and diseases – meaning they are affected for years after the someone has lost excess body fat.
The findings, from the University of Birmingham, show that the body can effectively remember the impact obesity had on it for between five and 10 years.
It means people may remain at risk of developing serious complications even after losing weight.
Professor Claudio Mauro, the co-lead author of the study from the department of inflammation and ageing at the University of Birmingham, said: ‘The findings suggest that short-term weight loss may not immediately reduce the risk of some disease conditions associated with obesity, including type 2 diabetes and some cancers.’
To analyse the long-term effects that obesity has on the body, researchers took blood samples from four groups of people over a 10-year period.
This included obese patients taking weight-loss injections, as well as those with Alstrom syndrome – a rare genetic disorder linked to obesity as it causes people to be less physically active.
They also collected blood and fat tissue from people who took part in a 10-week exercise programme, and from people living with obesity who had osteoarthritis and were undergoing hip or knee replacement surgery.
The risk of developing complications such as type 2 diabetes and cancer may not fully disappear after losing weight from obesity, a study has found
Furthermore, the researchers studied mice on a high-fat diet and blood donations from healthy human volunteers.
Their study found that immune cells – known as helper T cells or CD4+ lymphocytes – carried a memory of obesity through a process called DNA methylation.
This causes the ‘tagging’ effect on DNA in immune cells, which can lead to problems such as reduced waste clearance and a less healthy immune system for up to a decade – which can lead to serious complications such as metabolic diseases and cancers.
Professor Mauro said that the findings show that weight loss may need to be maintained for several years, but said there should be further studies into their results.
He also said the findings could support the use of SGLT2 drugs – normally used to treat type 2 diabetes, heart failure and chronic kidney disease by triggering the body to release excess glucose in the urine – because they have ‘shown promise’ in helping the immune system in those with obesity.
Obesity now affects more than one billion people worldwide and continues to rise across Europe, fuelled by unhealthy food environments, urban design that discourages physical activity, and widening social inequality.
In the UK, an estimated one in 50 adults are now using fat jabs, with demand surging since the National Institute for Health and Care Excellence (NICE) approved Wegovy for NHS use in 2023.
Despite that, nearly two-thirds of adults in the UK are overweight and more than a quarter are obese, equivalent to around 14 million people.
For adults, having a body mass index (BMI) of between 30-39.9 is classed as obese by the NHS, while anything more than 40 is seen as severely obese.
Obesity has been found to trigger a number of serious health complications including type 2 diabetes, heart disease, breast cancer, bowel cancer and stroke.
More than 18,000 preventable cancer cases in Britain are currently linked to obesity, making it the second biggest cause of the disease behind smoking.
Dr Belinda Nedjai, senior author of the paper from the Wolfson Institute of Population Health at Queen Mary University London, said: ‘Our findings show that obesity is associated with durable epigenetic modifications that influence immune cell behaviour.
‘This suggests that the immune system retains a molecular record of past metabolic exposures, which may have implications for long-term disease risk and recovery.’
