A scientific study published in the journal Nature reveals that even after significant weight loss, the body's fat cells retain a "memory" of obesity. This finding may help explain why it can be challenging to maintain weight loss, as stated in the article detailing the research conducted by scientists from Switzerland and the United States.
This type of "memory" arises because obesity leads to changes in the epigenome—a collection of chemical tags that can be added or removed from the DNA of cells and proteins, which help increase or decrease gene activity. For fat cells, the shift in gene activity seemingly renders them incapable of normal function, presenting a discouraging conclusion from the authors of the study. This disruption, along with changes in gene activity, can persist long after weight has decreased to a healthy level.
"The results indicate that individuals trying to lose weight often require long-term support to avoid regaining it. This is not their fault," explains co-author Laura Hinte, a biologist at the Swiss Federal Institute of Technology Zurich (ETH) in Zurich.
It has long been known that weight gain often occurs after weight loss. However, there was no scientific explanation for this phenomenon. The new study shows that this happens at the molecular level, adds Hyun Chul Ro, an epigenomics expert from the Indiana University School of Medicine in Indianapolis (USA).
To understand why weight can return quickly after loss, Hinte and her colleagues analyzed fat tissue from a group of individuals with severe obesity, as well as from a control group of individuals who had never experienced obesity. They found that some genes were more active in the fat cells of the obese group than in those of the control group, while other genes were less active.
As noted in the article, even weight-loss surgery did not alter this pattern. Two years after participants with obesity underwent weight-loss surgeries, they had lost a significant amount of weight, but the genetic activity in their fat cells still exhibited a pattern associated with obesity.
Scientists observed similar results in mice that had lost a considerable amount of weight: changes in their epigenomes persisted, as if the cells "remembered" being part of an obese organism. These cells absorbed more sugar and fat than the fat cells of control mice that had never suffered from obesity. Previously obese mice gained weight more rapidly on a high-fat diet than the control mice.
However, co-author Ferdinand von Meyenn, an epigenomics expert from ETH, emphasizes that while there is a connection between "cell memory" and subsequent obesity, it is not causal. He adds that preventing obesity from the very beginning is crucial. People who lose weight "can [remain] slim, but it will require a lot of effort and energy," warns von Meyenn, adding that his team's findings may help reduce the stigma associated with obesity.