‘Remembering’ fat from past obesity fuels the yo-yo dieting effect, experts say
Losing weight can be a frustrating game: After months of successful weight loss, the pounds can quickly pile back up, leaving people right back where they started.
There is no one factor that causes the yo-yo effect, but new research points to fat tissue as the main culprit. Fat ‘remembers’ past obesity and resists weight loss efforts, scientists have found.
Researchers identified biological memory after examining fat tissue from obese people before and after they lost weight after bariatric surgery. The tissues were further compared to the fat of healthy individuals who had never been obese.
The analysis found that obesity affected fat cells in ways that changed the way they responded to food, possibly for years to come. In tests, the cells grew faster than others by absorbing nutrients more quickly.
Professor Ferdinand von Meyenn, a senior author of the study at the Federal Institute of Technology in Zurich, said: “Our research indicates that one of the reasons why it is difficult to maintain body weight after initial weight loss is that fat cells remember their previous obese state and likely goal to return to this state.
“Memory appears to prepare cells to respond more quickly, and perhaps in an unhealthy way, to sugars or fatty acids.”
Further research on mouse cells has traced biological memory to chemical modifications on DNA or the proteins around which DNA is wrapped. These epigenetic changes alter gene activity and metabolism.
To enrol Naturescientists describe how previously obese mice gained weight faster than others when fed a high-fat diet, indicating a shift in metabolism that made it easier for them to gain weight. However, the memory of obesity in the fat cells was not solely to blame. The scientists suspect that a similar memory exists in brain cells that influences how much food animals consume and how much energy they expend.
Dr. Laura Hinte, first author of the study, said: “From an evolutionary perspective, this makes sense. Humans and other animals have adapted to defend their body weight rather than lose it, as food scarcity has historically been a common challenge.”
Almost two-thirds of adults in England are overweight or obese, and the condition affects more than a billion people worldwide. Obesity is costing the NHS £6.9 billion per year and is the second largest preventable cause of cancer.
Another researcher, Dr Daniel Castellano-Castillo, said: “On a societal level, this could provide some comfort to people struggling with obesity.” Struggling to keep the pounds off may be caused by a cellular memory that is “actively resistant to change,” he said.
The work could pave the way for better weight management programs, although the cellular memory of obesity may also fade over time. “It’s possible that maintaining a reduced or healthy body weight for long enough is enough to erase the memory,” says Hinte.
Professor Henriette Kirchner from the University of Lübeck called the finding “very plausible”. “I’m convinced it plays an important role in the yo-yo effect after dieting,” she said. “The researchers convincingly show that the memory becomes more difficult to erase the longer you are obese.”
People who lose weight by following a diet or after taking slimming pills such as Wegovy usually regains weight when they stop.
David Benton, emeritus professor at Swansea University and author of the 2024 book Tackling the Obesity Crisis: Beyond Failed Approaches to Lasting Solutions, said more than 100 factors influence obesity.
“Obesity reflects consuming more calories than you burn. When dieting removes energy, you lose weight,” he said. “The mantra, however, is that diets fail. They fail because in order to avoid regaining the weight you lost, you must permanently change your diet. Usually, after we finish the diet, we return to the lifestyle that caused the problem in the first place. The result is a yo-yo diet.”