Why does the weight return? Because your body doesn't want to let go of it

Losing weight is a tedious process, especially since shedding it off does not guarantee that it will stay away forever. Scientists have now found why the weight returns easily for some people, also known as the dreaded yo-yo effect. They have blamed it on fatty tissue, and say that the fat “remembers” being obese. When you try to lose weight, it resists the attempts and can pile it back on.

Researchers at ETH Zurich say that this phenomenon is rooted in epigenetics. "Epigenetics tells a cell what kind of cell it is and what it should do,” says Laura Hinte, a doctoral student who was part of the study.

Led by Ferdinand von Meyenn, Professor of Nutrition and Metabolic Epigenetics, it has been published in the journal Nature.

The researchers studied cells from overweight mice and the ones that had lost excess weight through dieting. They found that obesity leads to characteristic epigenetic changes in the nucleus of fat cells. The changes remain present even after a diet. 

“The fat cells remember the overweight state and can return to this state more easily,” von Meyenn says.

Obesity has a lasting effect on the fat cells, affecting the way they respond to food. The tests found these cells to grow faster than others by absorbing nutrients more swiftly.

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Formerly obese mice gained weight faster

In the mice, scientists found that those with these epigenetic markers, or the ones that were formerly obese, regained weight more quickly upon consuming a high-fat diet. "That means we’ve found a molecular basis for the yo-yo effect," the researchers said.

“Fat cells are long-lived cells. On average, they live for ten years before our body replaces them with new cells,” Hinte says.

The researchers say that right now it is not possible to change the relevant epigenetic marks in the cell nucleus with drugs and "erase the epigenetic memory."

Von Meyenn adds that this memory effect is the reason why it’s "so important to avoid being overweight in the first place. Because that’s the simplest way to combat the yo-yo phenomenon." 

Their study is primarily aimed at children and young people and their parents.

Meanwhile, fat cells might not be the only ones in our body that store this memory, researchers say. "Other body cells might also play a part in the yo-yo effect," von Meyenn says. 

It is possible that the cells in the brain, blood vessels or other organs also remember obesity and contribute to the yo-yo effect. However, further studies are needed to understand whether this is true.