Scientists have uncovered previously unknown benefits of shedding excess weight, including that it helps to clear out damaged and ageing cells within the body.
A groundbreaking study, published in the journal Nature, conducted the first highly detailed analysis of changes that weight loss causes in human fat tissue, examining hundreds of thousands of cells.
Beyond the cellular clearance, researchers also identified an increased metabolism of harmful fats.
These findings could pave the way for future therapies targeting conditions such as type 2 diabetes.
The research compared fat tissue samples from individuals of a healthy weight with those suffering from severe obesity (with a BMI over 35) who were undergoing bariatric weight loss surgery.
The weight loss cohort provided samples during surgery and again more than five months later, by which point they had lost an average of 25kg.
Researchers from the Medical Research Council (MRC) Laboratory of Medical Sciences in London, and from Imperial College London, analysed gene expression in more than 170,000 cells that made up the fat tissue samples, from 70 people.
They discovered that weight loss triggers the breakdown and recycling of fats called lipids.
This recycling process could be responsible for burning energy and reversing the harmful build-up of lipids in other organs like the liver and pancreas, they said.
Further research is now needed to work out if lipid recycling is linked to the positive effects of weight loss on health, such as remission of type 2 diabetes.
Scientists also found that the weight loss cleared out senescent cells, which are ageing and damaged cells that accumulate in all tissues.
These cells no longer function properly and release signals that lead to tissue inflammation and scarring.
“We’ve known for a long time that weight loss is one of the best ways to treat the complications of obesity, such as diabetes, but we haven’t fully understood why,” Dr William Scott, who led the study, said.
“This study provides a detailed map of what may actually be driving some of these health benefits at a tissue and cellular level.
“Fat tissues have many under-appreciated health impacts, including on blood sugar levels, body temperature, hormones that control appetite, and even reproductive health.
“We hope that new information from studies like ours will start to pave the way for developing better treatments for diabetes and other health problems caused by excess body fat.”
Researchers found that weight loss did not, however, improve the effects of obesity on some aspects of the immune system.
Inflammatory immune cells, for example, did not fully recover even after weight loss.
Experts said this type of inflammatory cell memory could be harmful in the long term if people regain weight.
The study was funded by the Medical Research Council, Diabetes UK and Wellcome.
Dr Faye Riley, research communications lead at Diabetes UK, said: “For some people, losing weight can put their type 2 diabetes into remission.
“But weight loss is challenging, and current approaches don’t work for everyone.
“This research offers a rare window into the changes that occur in fat tissue during weight loss that may be key to improving health and putting type 2 diabetes into remission.
“By deepening our understanding of these processes, the study could open the door to innovative therapies that mimic the effects of weight loss, potentially helping people with type 2 diabetes to manage their condition or go into remission.”